Evaluation of real-time polymerase chain reaction for the diagnosis of protozoal myeloencephalitis in horses using cerebrospinal fluid.
Authors: Enriquez Carla Katherine, Morrow Jennifer K, Graves Amy, Johnson Amy
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Real-Time PCR for Equine Protozoal Myeloencephalitis Diagnosis Diagnosing equine protozoal myeloencephalitis (EPM) caused by *Sarcocystis neurona* remains frustratingly imprecise in living horses, relying heavily on serological testing and clinical signs rather than direct pathogen detection. Enriquez and colleagues evaluated whether real-time PCR (rtPCR) analysis of cerebrospinal fluid could improve diagnostic accuracy by testing CSF samples from 99 horses with neurological disease—52 with confirmed or presumptive EPM and 47 with other diagnoses (equine degenerative myeloencephalopathy, cervical stenotic myelopathy, trauma, or necropsy-confirmed normal findings). The results were sobering: rtPCR detected *S. neurona* in only one sample, obtained from a horse with confirmed EDM rather than EPM, yielding a sensitivity of 0% despite testing horses with necropsy-confirmed disease. Although the specificity appeared excellent (one false positive amongst 47 negative cases), the complete absence of true positive detections means rtPCR on CSF cannot reliably exclude EPM and offers no practical advantage over existing diagnostic methods for clinicians. For farriers, physiotherapists, and coaches working with neurologically affected horses, this finding underscores that current diagnostic decisions will continue to depend on serology (SnSAG2/4/3 ELISA serum:CSF ratios), clinical presentation, and response to treatment rather than direct pathogen identification—emphasising the importance of collaborative veterinary assessment when EPM is suspected.
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Practical Takeaways
- •Do not rely on S. neurona rtPCR of cerebrospinal fluid as a diagnostic test for EPM; the test shows poor sensitivity and may miss cases
- •Continue using SnSAG2/4/3 ELISA serum:CSF titer ratios (cutoff <50) as the more reliable diagnostic criterion for presumptive EPM diagnosis
- •Be aware that negative rtPCR results do not rule out EPM and should not be used to exclude the diagnosis in clinically suspect horses
Key Findings
- •Real-time PCR for S. neurona on cerebrospinal fluid demonstrated 0% sensitivity for EPM diagnosis in the study population of 52 EPM cases
- •Only 1 of 99 samples was weakly positive by rtPCR, obtained from a horse with necropsy-confirmed EDM rather than EPM
- •All 98 remaining samples from EPM-confirmed, presumptive EPM, and other neurologic disease cases were negative for S. neurona by rtPCR
- •Results contradict previous reports suggesting S. neurona rtPCR on CSF as a promising diagnostic tool for EPM