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Case Analysis

Clinical signs of EPM vary from acute to chronic. Often signs of neuromuscular disease include weakness, unusual or atypical lameness, behavior changes, seizures, and recurring signs after treatment. Using a decision tree EPM Chart  may help you form a diagnostic plan.

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Please fill in this short survey if you have used diclazuril to treat EPM in your horse.


For an accurate antemortem diagnosis conduct a complete neurologic examination, evaluate the gait and assign a Gait Assessment Score  or Fordyce Score. Signs that occur during acute infection can be overlooked, Early Signs 2003  Rule out other causes of neurologic disease using radiographs (cervical) or ultrasound and other available tools.

It is possible for other diseases to look alike EPM.  A good clinical history and recognizing multiple "EPM" treatments can help determine relapsing disease.  For a discussion of the diseases that should be considered read, Diseases Associated with EPM 2017.

Use immunodiagnostic testing of serum and CSF. Determine the suitability of the case for field trial enrollment, review the parameters for enrollment on the Clinical Trial tab. Submit samples for testing using the Equine Consultation Form.  The appropriate initial tests for suspect EPM are the SAG 1, 5, 6 for sarcocystosis and the CRP.  Your sample will be saved for 6 months in case additional testing is required.  Review the test results, EPM Chart and if necessary, call for advice on additional testing.

Determine the appropriate treatment.  The most complete information on licensed treatments for S neurona can be found in the Freedom of Information summary, FOI Marquis FIS Protazil and ReBalance-FOIS.  The expectation of effectiveness can be determined from these documents, pay attention to what constitutes a "successful" treatment, sometimes success is change from a positive to a negative test result without any improvement in the clinical signs. Qualified horses can enroll in field trials.  The field trials and safety studies allow us to write our FOI.  Review the qualifications for inclusion criteria, sign the Owner Consent Form, the forms are trial specific. To enter the trial you may need additional documentation and testing,  be sure to call prior to treatment. In some studies there is a "wash out" period before entering our field studies.

Post-treatment evaluation is important.  We recommend a post-treatment examination at 10 days after initiating treatment in one study or 14 days in another study.  Assess the gait score and complete a second form, Gait Assessment Score.  If the horse has not returned to a GAS 0, call us to discuss the case. If the horse has a chronic relapsing history consider an alternate diagnosis, polyneuritis or sarcocystosis due to S. fayeriPolyneuritis equi Ellison 2015 and Ellison 2015 Polyneuritis equi assay or 2016 S fayeri.

Sometimes it is useful to obtain a muscle biopsy, especially in cases that aren't responding to treatment as expected.  Please refer to Bedford et. al. JAVMA, Vol 242, No. 8, April 15, 2013.  This refers to biopsy of the sacrocaudalis dorsalis medialis muscle biopsy specimens obtained 1 to 2 cm off of midline, 4 cm cranial to the tail head.  If a horse has received a diagnosis and treatment for polyneuritis equi in consultation with Pathogenes you may send the formalin fixed sample to us for histopathology.