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An Update on EPM: The Latest in Diagnostics and Treatment

December 6, 2010 Leave a comment

Jean-Yin Tan, DVM, DACVIM Large Animal Internal Medicine

Diagnostics

“My horse has been just a little off, Doc. I don’t really want to pay for a full-blown lameness or neuro exam or anything. Would you mind just taking a blood test for EPM while you’re here?”

If you’re a general equine practitioner, you’ve likely been asked a question like this in the middle of a routine vaccine visit, by a horse owner who’s been dabbling in reading a few of the latest horse publications and learning some catch phrases from her friends. Since you were hoping to just quickly knock off a few vaccines while on your way to 5 more lengthy calls that you have to cram into your afternoon, chances are you’ve been tempted to just pull the blood sample. After all, a full neurologic exam would take a lot of time and money, and that’s not what the owner wants to do, right?

It might be time to educate your client. The first rule of interpreting any diagnostic tests for EPM is that a clinical diagnosis of EPM must be made. In the absence of detectable neurologic deficits and elimination of other differential diagnoses, confirmation of exposure to Sarcocystis neurona via any number of diagnostic tests can mean very little.

Western Blot. Sensitivity is 80% and specificity 38% for testing of the serum of neurologic horses. That means it can be used to rule out EPM, but the low specificity means a large number of false positives, making the test inappropriate for diagnosing EPM. Cross-reaction may also occur with nonpathogenic Sarcocystis fayeri, which uses the horse as a natural intermediate host.

IFAT. The indirect immunofluorescent antibody test is a quantitative serologic test for EPM which provides actual titers and a likelihood ratio of the disease. Although sensitivity (83% for serum) is similar to that of the Western blot, specificity (97% for serum) is higher using the IFAT. Serum and CSF results have a moderately strong correlation. Furthermore, blood contamination of up to 104 RBCs/l does not affect CSF test results. The IFAT can also be used to detect EPM attributed to Neospora hughesii. There is however, cross-reaction with S. fayeri.

SAG-1 ELISA. The latest test is an ELISA that detects a specific surface antigen SAG-1 found on S. neurona merozoites. Although the low sensitivity and specificity (68% and 71% respectively) and geographical variation in presence of the surface antigen inhibits the commercially available SAG-1 ELISA from being a reliable diagnostic test, there is some potential for a more reliable SAG-2 ELISA in the future, especially given the lack of cross-reactivity with S. fayeri and N. hughesi.

So, what should I do? The Western Blot, IFAT, and SAG-1 ELISA are all different ways of detecting anti-S. neurona antibodies in serum or CSF. Currently, the IFAT offers the highest sensitivity and specificity. It is important, however, to take into consideration that cross-reaction with S. fayeri and vaccination can affect results.

CLICK TO SEE THE FULL CHART


Treatment
“Doc, I read in a horse magazine about a medication called toltrazuril? Do you think we should try that on my horse? I think it’s supposed to work real well on EPM.”

It’s busy season and you haven’t had much of a chance to sit down, let alone read the latest in journals on equine neurologic disease. If you’ve never heard of toltrazuril, don’t panic. I’ve put together a brief synopsis of drugs used for EPM below.

Antiprotozoals. FDA approved options are: sulfadiazine/pyrimethamine, ponazuril, nitazoxanide, and diclazuril. In the studies cited, successful treatment is defined as improvement in neurological grade by at least 1 level or CSF testing becoming negative on Western blot.

Sulfadiazine/pyrimethamine (ReBalance). At 20mg/kg sulfadiazine and 1mg/kg pyrimethamine orally daily for 90 days, 62% of affected horses have successful outcomes. However, adverse effects from folic acid deficiency include bone marrow suppression (12%), GI disturbance, decreased spermatogenesis in stallions, and congenital defects in foals when used in pregnant mares.

Ponazuril (Marquis). At 5mg/kg orally daily for 28 days, this antiprotozoal drug is responsible for the successful treatment of 60% of horses and at double-dose, 65% of affected horses. There were no adverse effects in a study of 101 horses. However, possible side effects listed by the manufacturer include blisters, hives, diarrhea, colic, and a seizure.

Nitazoxanide (Navigator). Although no longer commercially available, this antiparasitic drug used at 50mg/kg orally daily for 28 days has been found to successfully treat 57% of horses. However, fatal enterocolitis, fever, anorexia, lethargy are noted side effects and affect up to 31% of horses.

Diclazuril. This FDA-approved but unmarketed antiprotozoal drug has been used as pellets at 1mg/kg orally daily for 28 days with a 67% success rate. Adverse reactions that may not necessarily be correlated with the drug include laminitis or decline in neurologic status.

Toltrazuril (Baycox 5%). An anti-coccidial drug used in other species, this drug is being reviewed by the FDA for use in horses for EPM. At 5mg/kg orally daily for 10 days, it has been found in limited studies to achieve excellent absorption into CSF with no adverse effects.

Antiinflammatories. Nonsteroidal antiinflammatory drugs can help decrease initial worsening of signs during treatment associated with inflammatory response to the parasite. Corticosteroids are not recommended but single doses may help curb inflammation and allow antiprotozoal drugs to work. Many veterinarians use DMSO as well. There have been no clinical trials to support or refute the use of Vitamin E and thiamine supplementation.

Immunostimulants. Some veterinarians have advocated the use of immunomodulation with drugs such as Prioponibacterium acnes, mycobacterial cell wall extracts, levamisole, and alpha-interferon. These could potentially affect T cell-mediated immunity and stimulate macrophages. However, without further investigation, theoretical immunopathologic effects on the CNS should also be considered.

What do I do if the horse relapses? It is theorized that 10% of horses relapse within 3 years of discontinuation of therapy. Treatment options include longer duration of therapy (off-label doubling of the standard period of treatment), using higher doses of ponazuril, combining ponazuril with sulfadiazine/pyrimethamine, using twice-weekly continuous therapy with sulfadiazine/pyrimethamine, and possibly using anthelmintic levamisole as an immunostimulant.

So…What should I treat with? Currently the only commercially available antiprotozoal with the least reported adverse effects is ponazuril. However, look for other options such as diclazuril or toltrazuril appearing on the market in the future. Although conservative use of antiinflammatories is widely accepted, the efficacy of treatments such as DMSO, thiamine, Vitamin E, and immunostimulants has not been specifically investigated but can be used at your discretion.

UPDATE
The new SAG-2 and SAG-4,3 assays for EPM which are now available. These have possible advantages over the previous available assays because:

-These surface antigens are those most commonly expressed by S. neurona strains
-Quantitative test
-Provide serum/CSF ratios
The disadvantage is that both CSF and blood samples need to be submitted to provide accurate information.

References
1. Daft B, Barr, BC, Gardner, IA, et al. Sensitivity and specificity of western blot testing of cerebrospinal fluid and serum for diagnosis of equine protozoal myeloencephalitis in horses with and without neurologic abnormalities. J Am Vet Med Assoc 2002;221:1007-1013.

2. Duarte P, Daft, BM, Conrad, PA, Packham, AE, Gardner, AE. Comparison of a serum indirect fluorescent antibody test with two Western blot tests for the diagnosis of equine protozoal myeloencephalitis. J Vet Diagn Invest 2003;15:8-13.

3. Duarte P, Daft, BM, Conrad, PA, et al. Evaluation and comparison of an indirect fluorescent antibody test for detection of antibodies to Sarcocystis neurona, using serum and cerebrospinal fluid of naturally and experimentally infected, and vaccinated horses. J Parasitol 2004;90:379-386.

4. Dubey J, Lindsay, DS, Saville, WJA, et al. A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM). Vet Parasit 2001;95:89-131.

5. Furr M, McKenzie, H, Saville, WJA, et al. Prophylactic administration of ponazuril reduces clinical signs and delays seroconversion in horses challenged with Sarcocystis neurona. J Paristol 2006;92:637-643.

6. Granstrom D, Howe, D, Bentz, B, et al. Current treatments for equine protozoal myeloencephalitis. Equine Disease Quarterly 2007;16.

7. Hoane J, Morrow, JK, Saville WJ, et al. Enzyme-linked immunosorbent assays for detection of equine antibodies specific to Sarcocystis neurona surface antigens. Clin Diagn Lab Immunol 2005;12:1050-1056.

8. Johnson A. Evidence-based review of diagnosis and treatment of Sarcocystis neurona infection (Equine Protozoal Myeloencephalitis). AAEP 2009.

9. MacKay R. Equine essentials – equine protozoal myeloencephalitis: Managing relapses. Veterinary Technician 2008;29.

10. Reed S, Saville, WJ, Schneider, RK. Neurologic disease: Current topics in-depth. AAEP 2003.

11. Saville W, Dubey, JP, Oglesbee, MJ, et al. Experimental infection of ponies with Sarcocystis fayeri and differentiation from Sarcocystis neurona infections in horses. J Parasitol 2004;90:1487-1491.

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Categories: EPM, Equine, Neurology, Tan

Cool Recent Abstracts

April 30, 2009 Leave a comment

SMALL ANIMAL

Intracranial Arachnoid Cysts in Dogs

from Compendium by Curtis W. Dewey – Veterinary Answers Consultant, Peter V. Scrivani, Ursula Krotscheck, Sofia Cerda-Gonzalez, Kerry Smith Bailey, Dominic J. Marino

Intracranial arachnoid cyst (IAC) is an infrequently reported developmental disorder seen primarily in small-breed dogs. It usually occurs in the caudal fossa, in the region of the quadrigeminal cistern. Although still considered uncommon, IAC is being recognized more frequently in veterinary medicine, coinciding with the increased availability of magnetic resonance imaging. In this article, clinical information from previously reported cases of canine IAC is combined with additional case information from our hospitals. Similar to IAC in people, it is thought that canine IAC is often an incidental finding. When IAC is responsible for neurologic disease in dogs, generalized seizures and cerebellovestibular dysfunction are the most common clinical presentations. Medical therapy of IAC focuses on management of increased intracranial pressure and seizures, if the latter are part of the clinical complaints. Surgical therapy of IAC involves either cyst fenestration or shunting the excess fluid to the peritoneal cavity.

Peripheral Nucleated Red Blood Cells as a Prognostic Indicator in Heatstroke in Dogs

from JVIM by I. Aroch, G. Segev, E. Loeb, Y. Bruchim

Heatstroke in dogs is often fatal and is associated with a high prevalence of secondary complications. Peripheral nucleated red blood cells (NRBC) occur in dogs with heatstroke, but their association with complications and the outcome is unclear. Peripheral NRBC are common in dogs with heatstroke and have prognostic significance. Forty client-owned dogs with naturally occurring heatstroke. Prospective, observational study. Dogs were followed from presentation to discharge or death. Serum biochemistry and coagulation tests were performed at presentation. CBC and evaluation of peripheral blood smears were performed at presentation and every 12 hours. The relative and the absolute NRBC numbers were calculated. Presence of NRBC was observed in 36/40 (90%) of the dogs at presentation. Median relative and absolute NRBC were 24 cells/100 leukocytes (range 0[ndash]124) and 1.48 × 103/[mu]L (range 0.0[ndash]19.6 × 103/[mu]L), respectively. Both were significantly higher in nonsurvivors (22) versus survivors (18) and in dogs with secondary renal failure and DIC versus those without these complications. Receiver operator curve analysis of relative NRBC at presentation as a predictor of death had an area under curve of 0.92. A cut-off point of 18 NRBC/100 leukocytes corresponded to a sensitivity and specificity of 91 and 88% for death. Relative and absolute numbers of peripheral NRBC are clinically useful, correlate with the secondary complications, and are sensitive and specific markers of death in dogs with heatstroke, although they should never be used as a sole prognostic indicator nor should they replace clinical assessment.


Relationships between Low Serum Cobalamin Concentrations and Methlymalonic Acidemia in Cats

from JVIM by C. G. Ruaux, J. M. Steiner, D. A. Williams

Serum cobalamin concentrations below reference range are a common consequence of gastrointestinal disease in cats. Serum cobalamin [le] 100 ng/L is associated with methylmalonic acidemia. To determine the prevalence of cobalamin deficiency, defined by elevated serum methylmalonic acid (MMA), in cats with serum cobalamin [le] 290 ng/L, and the optimum serum cobalamin concentration to predict cobalamin deficiency in cats. Residual serum samples (n = 206) from cats with serum cobalamin [le] 290 ng/L. Retrospective, observational study. Serum cobalamin and folate were measured with automated assays. Serum MMA was determined by gas chromatography-mass spectrometry. Cobalamin deficiency was defined as serum MMA > 867 nmol/L. Sensitivity and specificity of serum cobalamin concentrations [le]290 ng/L for detecting MMA > 867 nmol/L were analyzed using a receiver-operator characteristic curve. There was a negative correlation between serum cobalamin and MMA concentrations (Spearman’s r=[minus]0.74, P 867 nmol/L. No significant difference in serum folate concentrations was detected between affected and unaffected cats. Elevated MMA concentrations, suggesting cobalamin deficiency, are common in cats with serum cobalamin [le] 290 ng/L. Cobalamin deficiency is clinically significant, and supplementation with parenteral cobalamin is recommended for cats with gastrointestinal disease and low serum cobalamin concentrations.

For more on MMA in human beings, click here.

Small Mammals
Single- and multiple-dose pharmacokinetics of marbofloxacin after oral administration to rabbits

From AJVR by James W. Carpenter, MS, DVM; Christal G. Pollock, DVM (VETERINARY ANSWERS CONSULTANT); David E. Koch, MS; Robert P. Hunter, PhD

Objective—To determine the pharmacokinetics of marbofloxacin after oral administration every 24 hours to rabbits during a 10-day period.

Animals—8 healthy 9-month-old female New Zealand White rabbits.

Procedures—Marbofloxacin (5 mg/kg) was administered orally every 24 hours to 8 rabbits for 10 days. The first day of administration was designated as day 1. Blood samples were obtained at 0, 0.17, 0.33, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 8, 12, and 24 hours on days 1 and 10 of marbofloxacin administration. Plasma marbofloxacin concentrations were quantitated by use of a validated liquid chromatography–mass spectrometry assay. Pharmacokinetic analysis of marbofloxacin was analyzed via noncompartmental methods.

Results—After oral administration, mean ± SD area under the curve was 10.50 ± 2.00 μg·h/mL and 10.90 ± 2.45 μg·h/mL, maximum plasma concentration was 1.73 ± 0.35 μg/mL and 2.56 ± 0.71 μg/mL, and harmonic mean terminal half-life was 8.0 hours and 3.9 hours for days 0 and 10, respectively.

Conclusions and Clinical Relevance—Marbofloxacin administered orally every 24 hours for 10 days appeared to be absorbed well and tolerated by rabbits. Administration of marbofloxacin at a dosage of 5 mg/kg, PO, every 24 hours is recommended for rabbits to control infections attributable to susceptible bacteria.

EQUINE
Risk Factors for Equine Postoperative Ileus and Effectiveness of Prophylactic Lidocaine

from JVIM by S. Torfs, C. Delesalle, J. Dewulf, L. Devisscher, P. Deprez
Postoperative ileus (POI) is a frequent and often fatal complication of colic surgery. Reliably effective treatments are not available. To determine risk factors and protective factors associated with POI, and to assess the effect of lidocaine IV on short-term survival. One hundred and twenty-six horses that underwent small intestinal colic surgery and that survived for at least 24 hours postoperatively. Retrospective cross-sectional study. The association of 31 pre-, intra-, and postoperative variables with POI and the association of lidocaine treatment with short-term survival were investigated. Associations were evaluated with univariable logistic regression models, followed by multivariable analysis. Significant associations of high heart rate (odds ratio [OR] = 1.05, 95% confidence interval [CI] 1.03[ndash]1.08), the presence of more than 8 L of reflux at admission (OR = 3.02, 95% CI 1.13[ndash]8.02) and the performance of a small intestinal resection (OR = 2.46, 95% CI 1.15[ndash]5.27) with an increased probability of POI were demonstrated. Prophylactic lidocaine treatment was significantly associated with a reduced incidence of POI (OR = 0.25, 95% CI 0.11[ndash]0.56). Lidocaine treatment was also significantly associated with enhanced short-term survival (OR = 0.30, 95% CI 0.09[ndash]0.98). The variables associated with an increased risk of POI can be useful in identifying horses at risk of POI and in providing a more accurate prognosis. The results are supportive for lidocaine IV as an effective prokinetic treatment after small intestinal colic surgery.

EHV-1 the neuropathogenic strain

April 29, 2008 Leave a comment

by Natalie Carrillo, MV, DVM, Dip ACVIM-LA

Recent outbreaks of myeloencephalopathy caused by equine herpesvirus (EHV-1) have generated new research that provides better information about diagnosis, treatment and outbreak management. The objective of this article is to summarize this information in a practical and applicable manner.

Clinical signs

The onset of EHV-1 myeloencephalopathy is characterized by a biphasic fever. In several outbreaks2 it has been observed that only horses younger than 5 years displayed fevers and respiratory signs, whereas the older horses were febrile, but had no signs of respiratory disease. It has also been observed that older horses develop neurologic deficits more frequently and of greater severity than younger horses (<5 y) 2. The reason for this bias is unknown, but may be explained by the role the horse’s immune system plays in the extent and severity of vasculitis and vascular thrombosis2.

The neurologic deficits appear approximately 4-6 days after the onset of fever2 and develop as the result of vasculitis, thrombosis and secondary ischemic degeneration of the neuropil1. The neurologic signs reflecting spinal cord involvement range from mild ataxia to recumbency, the pelvic limbs are more frequently involved and bladder atony is common. The brainstem may also be affected and therefore deficits of the cranial nerves may also be observed.

Epidemiology and outcome

The clinical signs are of rapid onset, but they also stabilize quickly. Most non recumbent animals do well, but the prognosis for recumbent horses is poor. In an outbreak of EHV-1 approximately 20-30 % of horses will be affected by the neuropathogenic strain, and of these the mortality will be approximately 30%1, 2.

Diagnosis

If you suspect a horse has EHV-1 due to an unexplained fever after being at an event, for example. A nasal swab and an EDTA purple top tube should be collected and submitted on ice packs overnight for real-time TaqMan® PCR on both samples to diagnose and differentiate the neuropathogenic vs non neuropathogenic strains. Results will be ready in 24h post arrival3. (See references for mailing addresses).

Outbreaks and treatment

In the event of a suspected outbreak there are guidelines on the AAEP website http://www.aaep.org/control_guidelines_nonmember.htm that pertain to biosecurity and quarantine. They are to extensive to cover, and are not the objective of this article. What I do want to incur into are treatment guidelines.

On the onset of fever of a suspected animal:

First implement biosecurity measures including stall confinement. Collect pertinent samples for diagnosis and then initiate therapy with NSAIDs such as flunixin meglumine 1.1 mg/kg or phenylbutazone 4.4mg/kg to manage the fevers.

Once the disease is confirmed or clinical signs of the disease progress to a working diagnosis of EHV-1, then more aggressive therapy and prophylaxis of surrounding animals should be initiated. All animals possibly exposed should be treated with Valacyclovir (Valtrex®) 205-403 mg/kg PO every 8 hours. Acyclovir despite clinical reports of effectivity2 has shown not to reach adequate serum levels to inhibit viral replication6 therefore should not be the first drug of choice. Valtrex® is an expensive drug and this option should be thoroughly discussed with the owner.

Management for the horses displaying clinical signs of the neuropathogenic form of EHV-1:

· NSAIDs – continue flunixin meglumine 1.1mg/kg for 10 d (monitor serum creatinine every 3-5d depending on hydration status of the horse).

· DMSO (if you are a believer) 1g/kg at 20% sol IV every 24h for 3 days, as a free radical scavenger.

· Valacyclovir (Valtrex®) 205-403 mg/kg PO every 8 hours for 10 days or until clinical signs stabilize.

· Vitamin E 10.000 IU PO every 24h for 10 days7 as an antioxidant.

· Dexamethasone 0.1 mg/kg IV for 3 days then taper for a total of 10d. This therapy is controversial. On one hand it is a potent anti-inflammatory, but on the other it does suppress the immune system at these doses. And never forget the potential for laminitis. I would reserve this choice of therapy for horses showing neurological deficits, I would not administer to horses with just a fever, even if it is a confirmed case.

· If at any point a horse should become recumbent or needs assistance standing, or in general deteriorates to the point of requiring constant monitoring please talk to the client about referral to a hospital with facilities for critical care.

Vaccination in an outbreak

From http://www.vetmed.ucdavis.edu/ceh/topics-EHV-1-vaccinations.htm

· On premises with confirmed clinical EHV-1 infection, booster vaccination of horses likely to be exposed is not recommended.

· Non-exposed horses or horses that have to enter the premises should have a booster vaccination if they have not been vaccinated within the past 90 days. This does not guarantee protection against the disease; the hope is that reduced nasal shedding of infectious EHV-1 by these horses will help reduce the magnitude of challenge experienced by other horses and potentially help reduce spread.

· A current publication8 showed that recent vaccination with Rhinomune (modified live vaccine) may provide some protection against EHV-1 myeloencephalopathy. These results should be interpreted with caution because the number of animals used in the study was small.

· Vaccines that provide the highest levels of viral neutralizing titers are Pneumabort, Prodigy, Calvenza and Rhinomune. The high levels of antibodies have been shown to reduce viral shedding. It is important to warn clients of the potential side effects of the modified live vaccine such as swelling of the injection site, fever and swelling of the limbs.

I hope this article has been helpful, if you should have any further questions about a case please do not hesitate to contact me.

References:

1.- Julia H. Kydd and K.C. Smith, Equine Herpesvirus Neurologic Disease: Reflections from across the pond. J Vet Intern Med. 2006 May-June;20(3):467-68.

2.- Henninger RW, et al, Outbreak of neurologic disease caused by equine herpesvirus-1 at a university equestrian center. J Vet Intern Med. 2007 Jan-Feb;21(1):157-65.

3.- Allen GP, Development of a real-time polymerase chain reaction assay for rapid diagnosis of neuropathogenic strains of equine herpesvirus-1.J Vet Diagn Invest. 2007 Jan;19(1):69-72. M.H. Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546.

4.- Garré B, et al, Pharmacokinetics of acyclovir after intravenous infusion of acyclovir and after oral administration of acyclovir and its prodrug Valacyclovir in healthy adult horses. Antimicrob Agents Chemother. 2007 Dec;51(12):4308-14. Epub 2007 Sep 10.

5.- BG Bentz, et al, Pharmacokinetics of Valacyclovir in the adult horse. Abstract #108 J Vet Intern Med. 2007 May-June;21(3):601.

6.- BG Bentz et al, Pharmacokinetics of Acyclovir after Single Intravenous and Oral Administration to Adult Horses. J Vet Intern Med. 2006 May-June;20(3):467-68.

7.- J.K. Higgins, et al, Vitamin E levels in serum and cerebrospinal fluid of healthy horses following oral supplementation. Abstract #340 J Vet Intern Med. 2007 May-June;21(3):666.

8.- Goodman LB, et al, Comparison of the efficacy of inactivated combination and modified-live virus vaccines against challenge infection with neuropathogenic equine herpesvirus type 1 (EHV-1).

Vaccine. 2006 Apr 24;24(17):3636-45. Epub 2006 Feb 13.

Disorders of the Brain Part I: Update on current trends, diagnostic tools, and treatments of congenital encephalopathies

March 12, 2008 1 comment

By Georgina Barone, DVM, DACVIM (Neurology)

Canine congenital encephalopathies comprise a broad range of developmental disorders. Clinical signs are dependent upon the area of the brain affected and may indicate whether the patient has focal, multifocal, or diffuse disease. A thorough neurologic examination is essential to determine neuroanatomic localization and make appropriate diagnostic and treatment recommendations. It is also imperative that other diseases that may contribute to neurologic deficits be ruled out such as hypoglycemia, porto-systemic shunts, infectious diseases, and inborn errors of metabolism. When evaluating a dog with a suspected intra-cranial developmental anomaly, the veterinarian should consider the following factors. First, is the abnormality of clinical significance? Some anomalies do not produce clinical signs and must be interpreted in light of the patient’s condition. Second, the animal must be evaluated for other malformations. Embryologic development of the brain is closely related to that of the spine and other tissues. Critical evaluation of all organ systems is essential to determine the viability of the dog as a pet. Heritability of the problem is also of key importance to the breeder, although many anomalies occur as sporadic occurrences. Lastly, treatment options and quality of life concerns must be addressed as many anomalous conditions of the CNS carry a guarded to poor prognosis with them.

This article will provide information on some of the more common congenital anomalies seen in our canine patients. Acquired disorders will be addressed in a future newsletter.

Quadrigeminal cysts (QC) are widely believed to be developmental anomalies that arise in close proximity to an intra-cranial arachnoid cistern, most commonly the quadrigeminal cistern located above the cerebellum. They represent accumulation of cerebrospinal fluid between sheets of the arachnoid layer of the meninges and lack an epithelial lining, thus are considered “pseudo-cysts”. Once thought to be rare, these anomalies are increasingly being recognized, most likely due to the greater availability of advanced imaging such as CT and MRI.

Small-breed dogs, particularly brachycephalic breeds (especially Shih-tzu’s) and male dogs are over-represented. Although clinical signs can be variable, one of the most common signs are generalized seizures, likely due to the pressure on the occipital lobes of the cerebrum by pressure from the cystic mass. Additionally, ataxia, intention tremors, paresis, and head tilt have all been reported. Support for the developmental nature of this disease stems from the fact that most patients are young (<1 year) of age when diagnosed and histopathology fails to reveal evidence of concurrent scarring, hemorrhage, infection, or inflammation. Occasionally, QC’s are found as incidental findings, either on necropsy or brain imaging.

fig-1-crop.jpg Figure 1 – Arachnoid Cyst

fig-2-crop.jpg Figure 2 – Arachnoid Cyst

Diagnosis of arachnoid cysts requires advanced imaging, preferably MRI or 3-D CT scanning. MRI (see Figures 1 & 2) will reveal a mass lesion rostro-dorsal to the cerebellum and caudal to the occipital lobes. The lesion appears hyper-intense on T2 images and hypointense on T1 images and is non-contrast enhancing. The quality of the lesion is virtually indistinguishable from cerebrospinal fluid. Variable degrees of compression and distortion of the adjacent cerebellum and cerebrum can be observed. Concurrent hydrocephalus has been reported, but this is likely a breed-related variant of ventricle size and unlikely to be of clinical significance. QC must be differentiated from cystic neoplasia or cysts associated with infectious disease (e.g. hydatid cyst).

Treatment of QC’s include surgery (fenestration, shunting, or marsupialization) or medical management (e.g. corticosteroids and carbonic anhydrase inhibitors), but controversy still remains over the preferred treatment. Prognosis must be considered guarded and the majority of dogs require life-long anticonvulsant therapy, even if surgical correction is performed.

Hydrocephalus refers to an increased volume of cerebrospinal fluid within the ventricular system and is most commonly recognized within the first few months of a dog’s life. The pathophysiology of congenital hydrocephalus is complex and mutifactorial but may be associated with fusion of the rostral colliculi, pre-natal infections causing stenosis of the mesencephalic aqueduct, compromise of cerebral vasculature, and intrauterine toxicity. Breeds at risk include Chihuahua’s, Yorkshire Terrier’s, Poodle’s, and a variety of brachycephalic breeds. Clinical signs generally are apparent prior to 6 months of age and are highly variable but usually include evidence of a prosencephalic disturbance. Abnormal mentation, visual deficits, circling, poor response to training, head pressing, seizures, and pacing have all been reported. Occasionally, hindbrain signs will predominate with ataxia, head tilt, abnormal nystagmus, and balance loss. Physical examination may reveal a large, dome-shaped head (Figure 3), calvarial defects, or an open fontanelle. Bilateral ventrolateral strabismus (“sunset eyes”) is seen as a sequelae to the skull malformation rather than as an indication of a vestibular disturbance.

figure-32-3.jpg

Figure 3 – Dome-shaped head in Hydrocephalus

Diagnosis is generally straightforward and is based on signalment, clinical signs, physical exam findings, and confirmation of ventriculomegaly. It must be understood that enlargement of the ventricles and the presence of an open fontanelle are not necessarily of any clinical significance. The patient must demonstrate signs of a brain disorder in the absence of any concurrent, active causal disease that may be responsible (e.g. encephalitis, metabolic encephalopathy). In patients with a patent fontanelle, the diagnosis may be confirmed with ultrasonography. Advanced imaging (CT, MRI) is the preferred method for imaging and confirming the diagnosis and for ruling out any concurrent disorders. MRI (Figure 4) will reveal dilation in the ventricular system and loss of the adjacent parenchyma.

fig-4-crop.jpg

Figure 4 – Hydrocephalus MRI

Treatment is aimed at reducing CSF volume and production. Prednisone or carbonic anhydrase inhibitors have been used with variable success. Surgical intervention is the treatment of choice and is aimed to divert CSF away from the ventricular system to the peritoneal cavity, pleural space, or right atrium. Ventriculoperitoneal shunting is the most common, technically feasible procedure done in domestic animals and can be done even on very small patients, such a Chihuahua’s. Prognosis is highly variable and depends on the degree of pre-operative neurologic dysfunction, chronicity, and avoidance of complications (infection, occlusion) associated with the shunt. Success rates as high as 90% have been reported with ventriculoperitoneal shunts, but owners must be advised that long-term prognosis for full return to function is guarded.

Chiari-Like Malformation (Caudal Occipital Malformation Syndrome or “COMS”) is a developmental anomaly that is being increasingly recognized as advances in neuroradiology are made. Anatomic abnormalities of the skull, specifically the occiput, result in compression of the structures of the caudal fossa and lead to cerebellar herniation. Consequently, there is alteration in the dynamics of cerebrospinal fluid flow and pressure on the cranial aspects of the spinal cord. Pressure gradients resulting from altered CSF flow as well as constriction of the cervicomeduulary junction at the foramen magnum result in the development of excessive fluid buildup within the spinal cord, either confined to the central canal (hydromyelia) or within the neuroparenchyma (syringomyelia). Collectively, the condition is referred to as syringohydromyelia (SM).

COMS is most often diagnosed in small breed dogs, especially Cavalier King Charles Spaniels. Other breeds being seen with increasing regularity include the Pomeranian, Pug, and other brachycephalic breeds. Affected animals can display a wide array of clinical signs including cerebellovestibular dysfunction, seizure activity, cervical/cranial hyperesthesia, or persistent scratching at the neck and shoulder region. Although it is considered to be a developmental disorder (most are diagnosed by 3 years), age at diagnosis can vary and clinical signs may not be evident until the animal is several years old. This is likely due to the fact that syringomyelia may take years to develop; the author has observed dogs that did not begin to display clinical signs until 7 or 8 years of age.

fig-5-crop.jpg Figure 5 – MRI of COMS & SM

fig-6-crop.jpg Figure 6 – MRI of COMS & SM

MRI is considered to be the diagnostic tool of choice to confirm COMS and SM (Figures 5 & 6). MRI findings in this condition include rostral displacement of the cerebellum by the occiput, obliteration of the dorsal subarachnoid space at the cervicomedullary junction, and cervical syringohydromyelia. Ventriculomegaly can also be observed but may be a normal variant in brachycephalic breeds and must be interpreted with caution. Additional diagnostics are currently being evaluated by researchers and include spiral CT scanning and brain-stem auditory evoked responses (BAER).

Medical management is directed toward relieving pain and decreasing CSF production. Commonly prescribed drugs include corticosteroids, narcotics, gabapentin, pregabalin, and carbonic anhydrase inhibitors. While medical therapy may effectively alleviate discomfort, long term prognosis is poor if the underlying anomaly is not addressed and treated. Progression of SM leads to pressure on the spinal cord parenchyma leading to permanent nerve damage and eventually intractable pain and paralysis. The treatment of choice in humans with COMS is Foramen Magnum Decompression (FMD) and the majority of human patients that undergo FMD either experience a halt in the progression or improvement in clinical signs. There is increasing evidence that FMD is the preferred method of treatment in dogs as well. Without surgery, more than 1/3 of dogs will be euthanized due to chronic severe pain and quality of life concerns. FMD allows for removal of hyperplastic occipital bone and relieves pressure on the underlying parenchyma. Often, SM will resolve or improve after the procedure, as evidenced by serial MRI exams. Unfortunately, in humans and animals, recurrence rate is high due to formation of scar tissue at the previous surgical site which in essence, recreates the original defect. A modification of the FMD in which titanium is placed over the defect created by the FMD to prevent excessive scar tissue has shown great promise with significantly fewer animals requiring re-operative procedures.

Other brain anomalies: Many other anomalies of the brain have been reported sporadically in dogs and should be considered when evaluating a pediatric patient with intracranial signs. Hydranencephaly has been reported in Labrador Retriever puppies and results from in utero destruction of previously viable neocortex during a critical period of development. Unlike hydrocephalus, the cranial cavity is of normal configuration. Imaging findings are similar to those seen with hydrocephalus but prognosis is extremely guarded. Lissencephaly (Figure 7) occurs when the normal cerebrocortical folds fail to develop, leading to an absence of gyri and sulci of the cerebral hemispheres. Lhasa Apso’s are most commonly affected, but the disease has also been reported in Irish Setters and Wire Hair Fox Terriers. Clinical signs include aggression, blindness, poor training ability, and generalized seizures. Seizures often do not occur until the animal is greater than 1 year of age and tend to be refractory to standard anticonvulsants. Prognosis is grave. Other defects in neuroparenchymal development (Figure 8 ) are seen infrequently and are poorly understood.

fig-7-crop.jpg Figure 7 – Lissencephaly

fig-8-crop.jpg Figure 8 – Defect in neuroparenchymal development

Disorders of the Brain Part I: Update on current trends, diagnostic tools, and treatments of congenital encephalopathies

March 12, 2008 Leave a comment
By Georgina Barone, DVM, DACVIM (Neurology)

Canine congenital encephalopathies comprise a broad range of developmental disorders. Clinical signs are dependent upon the area of the brain affected and may indicate whether the patient has focal, multifocal, or diffuse disease. A thorough neurologic examination is essential to determine neuroanatomic localization and make appropriate diagnostic and treatment recommendations. It is also imperative that other diseases that may contribute to neurologic deficits be ruled out such as hypoglycemia, porto-systemic shunts, infectious diseases, and inborn errors of metabolism. When evaluating a dog with a suspected intra-cranial developmental anomaly, the veterinarian should consider the following factors. First, is the abnormality of clinical significance? Some anomalies do not produce clinical signs and must be interpreted in light of the patient’s condition. Second, the animal must be evaluated for other malformations. Embryologic development of the brain is closely related to that of the spine and other tissues. Critical evaluation of all organ systems is essential to determine the viability of the dog as a pet. Heritability of the problem is also of key importance to the breeder, although many anomalies occur as sporadic occurrences. Lastly, treatment options and quality of life concerns must be addressed as many anomalous conditions of the CNS carry a guarded to poor prognosis with them.

This article will provide information on some of the more common congenital anomalies seen in our canine patients. Acquired disorders will be addressed in a future newsletter.

Quadrigeminal cysts (QC) are widely believed to be developmental anomalies that arise in close proximity to an intra-cranial arachnoid cistern, most commonly the quadrigeminal cistern located above the cerebellum. They represent accumulation of cerebrospinal fluid between sheets of the arachnoid layer of the meninges and lack an epithelial lining, thus are considered “pseudo-cysts”. Once thought to be rare, these anomalies are increasingly being recognized, most likely due to the greater availability of advanced imaging such as CT and MRI.

Small-breed dogs, particularly brachycephalic breeds (especially Shih-tzu’s) and male dogs are over-represented. Although clinical signs can be variable, one of the most common signs are generalized seizures, likely due to the pressure on the occipital lobes of the cerebrum by pressure from the cystic mass. Additionally, ataxia, intention tremors, paresis, and head tilt have all been reported. Support for the developmental nature of this disease stems from the fact that most patients are young ( Occasionally, QC’s are found as incidental findings, either on necropsy or brain imaging.

fig-1-crop.jpg Figure 1 – Arachnoid Cyst

fig-2-crop.jpg Figure 2 – Arachnoid Cyst

Diagnosis of arachnoid cysts requires advanced imaging, preferably MRI or 3-D CT scanning. MRI (see Figures 1 & 2) will reveal a mass lesion rostro-dorsal to the cerebellum and caudal to the occipital lobes. The lesion appears hyper-intense on T2 images and hypointense on T1 images and is non-contrast enhancing. The quality of the lesion is virtually indistinguishable from cerebrospinal fluid. Variable degrees of compression and distortion of the adjacent cerebellum and cerebrum can be observed. Concurrent hydrocephalus has been reported, but this is likely a breed-related variant of ventricle size and unlikely to be of clinical significance. QC must be differentiated from cystic neoplasia or cysts associated with infectious disease (e.g. hydatid cyst).

Treatment of QC’s include surgery (fenestration, shunting, or marsupialization) or medical management (e.g. corticosteroids and carbonic anhydrase inhibitors), but controversy still remains over the preferred treatment. Prognosis must be considered guarded and the majority of dogs require life-long anticonvulsant therapy, even if surgical correction is performed.

Hydrocephalus refers to an increased volume of cerebrospinal fluid within the ventricular system and is most commonly recognized within the first few months of a dog’s life. The pathophysiology of congenital hydrocephalus is complex and mutifactorial but may be associated with fusion of the rostral colliculi, pre-natal infections causing stenosis of the mesencephalic aqueduct, compromise of cerebral vasculature, and intrauterine toxicity. Breeds at risk include Chihuahua’s, Yorkshire Terrier’s, Poodle’s, and a variety of brachycephalic breeds. Clinical signs generally are apparent prior to 6 months of age and are highly variable but usually include evidence of a prosencephalic disturbance. Abnormal mentation, visual deficits, circling, poor response to training, head pressing, seizures, and pacing have all been reported. Occasionally, hindbrain signs will predominate with ataxia, head tilt, abnormal nystagmus, and balance loss. Physical examination may reveal a large, dome-shaped head (Figure 3), calvarial defects, or an open fontanelle. Bilateral ventrolateral strabismus (“sunset eyes”) is seen as a sequelae to the skull malformation rather than as an indication of a vestibular disturbance.

figure-32-3.jpg

Figure 3 – Dome-shaped head in Hydrocephalus

Diagnosis is generally straightforward and is based on signalment, clinical signs, physical exam findings, and confirmation of ventriculomegaly. It must be understood that enlargement of the ventricles and the presence of an open fontanelle are not necessarily of any clinical significance. The patient must demonstrate signs of a brain disorder in the absence of any concurrent, active causal disease that may be responsible (e.g. encephalitis, metabolic encephalopathy). In patients with a patent fontanelle, the diagnosis may be confirmed with ultrasonography. Advanced imaging (CT, MRI) is the preferred method for imaging and confirming the diagnosis and for ruling out any concurrent disorders. MRI (Figure 4) will reveal dilation in the ventricular system and loss of the adjacent parenchyma.

fig-4-crop.jpg

Figure 4 – Hydrocephalus MRI

Treatment is aimed at reducing CSF volume and production. Prednisone or carbonic anhydrase inhibitors have been used with variable success. Surgical intervention is the treatment of choice and is aimed to divert CSF away from the ventricular system to the peritoneal cavity, pleural space, or right atrium. Ventriculoperitoneal shunting is the most common, technically feasible procedure done in domestic animals and can be done even on very small patients, such a Chihuahua’s. Prognosis is highly variable and depends on the degree of pre-operative neurologic dysfunction, chronicity, and avoidance of complications (infection, occlusion) associated with the shunt. Success rates as high as 90% have been reported with ventriculoperitoneal shunts, but owners must be advised that long-term prognosis for full return to function is guarded.

Chiari-Like Malformation (Caudal Occipital Malformation Syndrome or “COMS”) is a developmental anomaly that is being increasingly recognized as advances in neuroradiology are made. Anatomic abnormalities of the skull, specifically the occiput, result in compression of the structures of the caudal fossa and lead to cerebellar herniation. Consequently, there is alteration in the dynamics of cerebrospinal fluid flow and pressure on the cranial aspects of the spinal cord. Pressure gradients resulting from altered CSF flow as well as constriction of the cervicomeduulary junction at the foramen magnum result in the development of excessive fluid buildup within the spinal cord, either confined to the central canal (hydromyelia) or within the neuroparenchyma (syringomyelia). Collectively, the condition is referred to as syringohydromyelia (SM).

COMS is most often diagnosed in small breed dogs, especially Cavalier King Charles Spaniels. Other breeds being seen with increasing regularity include the Pomeranian, Pug, and other brachycephalic breeds. Affected animals can display a wide array of clinical signs including cerebellovestibular dysfunction, seizure activity, cervical/cranial hyperesthesia, or persistent scratching at the neck and shoulder region. Although it is considered to be a developmental disorder (most are diagnosed by 3 years), age at diagnosis can vary and clinical signs may not be evident until the animal is several years old. This is likely due to the fact that syringomyelia may take years to develop; the author has observed dogs that did not begin to display clinical signs until 7 or 8 years of age.

fig-5-crop.jpg Figure 5 – MRI of COMS & SM

fig-6-crop.jpg Figure 6 – MRI of COMS & SM

MRI is considered to be the diagnostic tool of choice to confirm COMS and SM (Figures 5 & 6). MRI findings in this condition include rostral displacement of the cerebellum by the occiput, obliteration of the dorsal subarachnoid space at the cervicomedullary junction, and cervical syringohydromyelia. Ventriculomegaly can also be observed but may be a normal variant in brachycephalic breeds and must be interpreted with caution. Additional diagnostics are currently being evaluated by researchers and include spiral CT scanning and brain-stem auditory evoked responses (BAER).

Medical management is directed toward relieving pain and decreasing CSF production. Commonly prescribed drugs include corticosteroids, narcotics, gabapentin, pregabalin, and carbonic anhydrase inhibitors. While medical therapy may effectively alleviate discomfort, long term prognosis is poor if the underlying anomaly is not addressed and treated. Progression of SM leads to pressure on the spinal cord parenchyma leading to permanent nerve damage and eventually intractable pain and paralysis. The treatment of choice in humans with COMS is Foramen Magnum Decompression (FMD) and the majority of human patients that undergo FMD either experience a halt in the progression or improvement in clinical signs. There is increasing evidence that FMD is the preferred method of treatment in dogs as well. Without surgery, more than 1/3 of dogs will be euthanized due to chronic severe pain and quality of life concerns. FMD allows for removal of hyperplastic occipital bone and relieves pressure on the underlying parenchyma. Often, SM will resolve or improve after the procedure, as evidenced by serial MRI exams. Unfortunately, in humans and animals, recurrence rate is high due to formation of scar tissue at the previous surgical site which in essence, recreates the original defect. A modification of the FMD in which titanium is placed over the defect created by the FMD to prevent excessive scar tissue has shown great promise with significantly fewer animals requiring re-operative procedures.

Other brain anomalies: Many other anomalies of the brain have been reported sporadically in dogs and should be considered when evaluating a pediatric patient with intracranial signs. Hydranencephaly has been reported in Labrador Retriever puppies and results from in utero destruction of previously viable neocortex during a critical period of development. Unlike hydrocephalus, the cranial cavity is of normal configuration. Imaging findings are similar to those seen with hydrocephalus but prognosis is extremely guarded. Lissencephaly (Figure 7) occurs when the normal cerebrocortical folds fail to develop, leading to an absence of gyri and sulci of the cerebral hemispheres. Lhasa Apso’s are most commonly affected, but the disease has also been reported in Irish Setters and Wire Hair Fox Terriers. Clinical signs include aggression, blindness, poor training ability, and generalized seizures. Seizures often do not occur until the animal is greater than 1 year of age and tend to be refractory to standard anticonvulsants. Prognosis is grave. Other defects in neuroparenchymal development (Figure 8 ) are seen infrequently and are poorly understood.

fig-7-crop.jpg Figure 7 – Lissencephaly

fig-8-crop.jpg Figure 8 – Defect in neuroparenchymal development

Categories: Imaging, Neurology