One of the most important tests performed in horses with neurologic disease, such as equine protozoal myeloencephalitis (EPM), is a cerebrospinal fluid (CSF) tap. Unfortunately, many owners and some veterinarians are not particularly comfortable with some of the challenges that accompany this technique, thereby limiting its practical use. But veterinarians at Michigan State University (MSU) have recently developed an alternative technique to make collecting a CSF sample more convenient for all involved.
"The two most common methods for collecting CSF samples from horses is either at the base of the spine near the tailhead or from the base of the skull," explained Anthony Pease, DVM, MS, Dipl. ACVR, assistant professor of radiology and section chief of diagnostic imaging at MSU’s College of Veterinary Medicine.
The problem with the former technique is the probability that blood will contaminate the CSF sample. The problem with the latter technique is that the horse needs to be anesthetized and laid down to retrieve the sample. While not a major issue for healthy horses, neurologic horses recovering from anesthesia can be extremely dangerous to themselves and others.
Because CSF testing is important in diagnosing EPM (or ruling it out in horses suffering from a different neurologic disease), Pease and colleagues devised an ultrasound-guided method of collecting CSF.
"We sedated 17 horses and inserted a needle through the skin on the side of the neck, just behind the left ear," described Pease. "The needle was advanced into the spinal canal between the first and second cervical vertebrae using ultrasound guidance