Neurologic Examination of Horses in the Field (AAEP 2010)

What does a veterinarian look for when evaluating a horse for neurologic disease? Hint: The neurologic exam starts with simple field tests, not sophisticated imaging equipment. Amy Johnson, DVM, Dipl. ACVIM-LAIM, lecturer in clinical studies at the University of Pennsylvania, discussed field neurologic examination of horses at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md.

"Each clinician has his or her own method of performing a neurologic exam; the most important aspect (of the neurologic exam) is to develop a system and use it consistently to avoid overlooking abnormalities," she began.

She described four sections of the neurologic exam as follows:

  • Evaluation of mental status;
  • Cranial nerve examination;
  • Spinal reflexes and muscle evaluation; and
  • Gait and postural examination.

Under-saddle evaluation isn't required, and in fact Johnson recommended against this practice for safety reasons if a horse is showing neurologic signs.

Evaluating a Horse's Mental Status

First, Johnson watches the horse in its stall or paddock to see any encephalopathic behavior such as head-pressing, compulsive circling, blindness, seizures, or changes in mental status (these are generally obvious without handling the horse). If any of these signs are present, this leads to suspicion of neurologic disease and further investigation to rule out other causes of the behavior (such as pain or systemic disease.

Handling the horse further will require additional caution and might also lead her to modify her exam for safety reasons, she noted. Additionally, if a symptomatic horse has not been vaccinated for rabies or its rabies vaccination history is unknown, she recommended using gloves and limiting contact with the horse.

Cranial Nerve Examination

This phase of the exam evaluates the horse's cranial (head) nerves by looking at whether the horse has normal function of the head and related structures, such as head position, eye function, menace response (flinching from quick hand movement toward the eye), normal tongue movement/retraction, chewing ability, etc.

Signs such as nystagmus (repetitive eye twitching), a head tilt, weak tongue, jaw deviation, food coming out of the nose, weak eyelid function, drooping ear, or abnormal pupil response to light suggest compromised neurologic function.

Spinal Reflex, Muscle Evaluation

The next stage of the exam is to evaluate tail/anal tone and go over the horse systematically, usually testing with something like a pen, car key, or hemostats, to see if any nerve reflexes (skin flinching from the prodding) are abnormal. Neurologic disease signs could include excessive reaction (hyperesthesia) or areas of analgesia (no sensation), areas of abnormal sweating, and/or areas of muscle atrophy.

Gait/Posture Examination

Finally, Johnson evaluates the horse standing and in motion with a combination of straight-line walking, curves, serpentines, circles, backing, walking while the tail is pulled to either side, and walking up and down off curbs. Spastic motion, loss of balance, irregular or inappropriate foot placement, foot dragging, and inappropriate limb crossing all can indicate neurologic problems.

"This exam is designed to start with relatively easy maneuvers and increase in complexity to highlight subtle neurologic deficits," Johnson noted. Neurologic problems might cause the veterinarian to halt the exam for safety reasons.

If the veterinarian finds any abnormalities during any phase of the neurologic exam, Johnson said the vet should determine the most likely location of the neurologic problem based on the abnormalities observed and follow up with more advanced diagnostics targeting that area. She commented that recording the exam on video can help monitor the horse's progress, refresh your memory later, and allow slow-motion evaluation, which can help pick up subtleties.

"After abnormalities are confirmed and localized, construction of a differential diagnostic list becomes much easier, and both the diagnostic and therapeutic plans will fall into place," she concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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