How and When to Perform a Neurological Examination on the Farm

How and When to Perform a Neurological Examination on the Farm

Kile S. Townsend, DVM, MS, DACVIM (LAIM)

Performing a neurological examination on the farm is a doable, recommended, and useful skill to develop as an equine practitioner or large animal veterinarian. Horses may often be more relaxed and calmer in their home environment and therefore easier to examine from a neurological perspective. Also, some horses with severe neurological deficits are unsafe to load or transport in a trailer, necessitating on farm assessment of neurological status and recommendations for further diagnostic tests or treatments.

The neurological examination of the horse should always be accompanied by complete physical examination and history taking. This should include complete history, signalment, animal’s use, and the time of onset and progression of clinical signs. It is important to determine how long the owner has owned the animal, how long they believe the presenting complaint to be afflicting the horse, and if any other horses or animals on the property or in contact with the horse are displaying any abnormal clinical signs.

Before beginning a neurological assessment of a horse, it is important to gather all necessary items needed for examination. You will need: a bright light (ideally a transilluminator, ophthalmoscope, or small flashlight), a pair of hemostats, a towel (for blindfolding), and gloves. Also recommended: neurological examination form, pen/paper, laptop/tablet, or video/audio recording. Neurological examination forms can be found online, one such form compiled by specialists in conjunction with Boehringer Ingelheim can be found at: https://docs.boehringer-ingelheim.com/Equine-NeurologicalExam-Long-Form.pdf

There are many ways to systematically perform a neurologic evaluation of a horse, but it is important to remember to perform the examination in the same order each time, so as to be thorough, complete, consistent, and predictable. Some general points to remember when beginning a neurological examination include be safe, observe keenly, know what is normal (i.e., breed/age variations, etc.). You will likely have to tailor your examination to the individual horse (with respect to horse/human safety, horse personality, stability, and facilities being a few limiting factors) and to have to repeat the exam or parts of the exam (not much value in a single test). The examination should occur in two major phases: the static or standing examination and the dynamic or movement examination.

Standing examination (mental status, cranial nerve examination, reflex evaluation):

First, if possible, the horse should be observed in its natural environment without influence of a handler or restraint. Mentation, behavior, posture, and gait can be evaluated by observing interactions in the environment and with the handler (distance examination). The horse should then be restrained in a static position. The overall body condition, musculature, posture, and symmetry of the horse can be observed by walking completely around the horse and observing it from the front, back, and both sides. Observe for areas of patchy sweating or muscle fasciculations during this examination. It is important to move the forelock out of the way to evaluate facial symmetry and to move the tail to evaluate hindlimb musculature.

The cranial nerve evaluation should then be performed, with special attention being paid to the right vs. left side. There are many ways to perform a cranial nerve examination, but a complete examination should be performed during any neurological examination, if it is safe to do so. See Table 1 (created by Amy L. Johnson, DVM, Diplomate ACVIM-LAIM) for cranial nerves, their functions, and assessment in the

horse. It is important to always wear gloves when handling the mouth/tongue of a neurological animal or any animal that has encephalopathic signs or unknown rabies vaccination history to limit exposure. The tongue should be grasped and examined and pulled from each side of the mouth to evaluate withdrawal and tone. A horse may be fed a small amount of grain/treat/hay during the examination to evaluate prehension and swallowing.

Posture of the head, neck, trunk, tail, and limbs should be observed while standing. Observation of the horse’s posture will give you an idea of the horse’s level of conscious proprioception. Palpation of the head, neck, shoulders, back, rump, and limbs should be performed to assess body mass, symmetry, muscle tone, pain, and changes in skin temperature. The limbs should be flexed and extended manually in the standing horse, if possible. Transrectal palpation of the bladder or distal gastrointestinal tract may be warranted. The strength of the horse can be tested by pulling on the withers or the tail to one side vs the other.

Examination of reflexes in the standing horse are subjective and limited. The reflexes commonly assessed include the cervicofacial reflex (compare right side to left side rather than horse to horse), cutaneous trunci, thoracolaryngeal (“slap test”, best evaluated endoscopically), anal/perianal reflexes, and lordosis/kyphosis of the back when a hemostat is run on either side of the spine and over the rump (evaluate left side to right side).

Moving examination (gait and posture):

The horse should primarily be evaluated at the walk, unless the neurological deficits are very subtle. It is best to perform the moving part of the neurological examination in a large, enclosed area with relatively flat ground, if possible. An experienced handler should be asked to handle the horse. The handler should be asked to walk the horse in a straight line towards and away the examiner, as well as in a zig/zag fashion and with and without the head elevated. The horse should be made to back up in a straight line and initiate walking forwards after backing. The horse should be walked across different surfaces such as flat hard ground vs soft/deep footing to assess foot placement and adaptation to the different footing. If the farm has pole or Cavalettis, they can be arranged for the horse to navigate through. The horse should be directed into tight circles (while maintaining forward gait) in both directions. If a hill or curb is available, it is practical to walk the horse up and down the hill or curb and do so with and without head elevation. A tail pull can be performed when the horse is walking, and the near hind leg is bearing weight to assess strength, reaction, and limb placement. Ataxia should be graded by scoring each individual limb using the Mayhew grading system Grade 0-5. The ease with which a comprehensive neurological assessment of a horse’s movements can be undertaken often depends on the extent to which the animal has been trained; neurological assessments are invariably challenging in unruly or untrained individuals.

Some clinicians will perform foot-placing tests or conscious proprioception tests (CPs). This can be done by placing the hoof on its dorsum, placing one limb in front of the other, or placing one limb laterally to assess rate of replacement. Although potentially useful in some cases and in smaller animals, these tests are not generally regarded as extremely useful in detecting abnormalities, because neurologically normal horses have widely varied responses, and some well-trained or good-natured horses may be quite slow to replace their limbs. Hopping the horse on one thoracic limb may exacerbate thoracic limb weakness or hyper/dysmetria, but it is often unsafe, impractical, and not lucrative to perform this test. Extensive and careful gait analysis can give the veterinarian the most information regarding ataxia, proprioception, and weakness/paresis. Neurological evaluation is often coupled with lameness

evaluation, as the two assess the horse’s gait and can be used together to diagnose disorders of movement. Grading System for Ataxia According to Mayhew Grade 0: Normal strength and coordination Grade 1: Subtle neurological deficits only noted under special circumstances but mild (e.g., while walking incircles) Grade 2: Mild neurological deficits but apparent at all times/gaits Grade 3: Moderate deficits at all times/gaits that are obvious to all observers regardless of expertise Grade 4: Severe deficits with tendency to buckle, stumble spontaneously, and trip and fall. Grade 5: Recumbent, unable to stand

Neuroanatomical localization:

The nervous system is generally divided into brain, spinal cord, peripheral nerve, and autonomic nervous system. The brain can be further separated into general areas such as the forebrain (altered mental status, seizures, abnormal behavior), brainstem (altered mental status, cranial nerve deficits, central vestibular disease), and cerebellum (intention tremor, hypermetria, ataxia, menace deficit, shivers) for localization.

Defects in the spinal cord can be categorized into ‘upper motor neuron’ (signs include exaggerated/hypermetric gait, exaggerated reflexes, increased muscle tone) or ‘lower motor neuron’ (signs include weakness, hypometria/dragging limbs, diminished/absent reflexes, decreased muscle tone). See below (adapted from UC Davis – Neurological Examination in the Horse).

Neurolocalization C1-C5/6/7 – UMN deficits (normal to exaggerated) of thoracic and pelvic limbs. C6-T2 – LMN signs of thoracic limbs, UMN of pelvic limbs. T3-L3 – Normal thoracic limbs, UMN of pelvic limbs. L4-S1 – Normal thoracic limbs, LMN of pelvic limbs. S-caudal – Normal thoracic limbs, normal or LMN of pelvic limbs depending on location, and cauda equina signs (e.g., urinary +/- rectal incontinence)

The peripheral nerves can be affected and resulting abnormalities will be specific to the nerves affected (i.e., radial nerve paralysis, tibial nerve paralysis, etc.). Peripheral neuropathies in large animals can often ben attributed to trauma or crush/down animals, but there are a variety of differential diagnoses that could be explored if history does not fit with trauma.

It is important to remember when performing a neurological examination of a horse to document as you go and to repeat tests more than once to demonstrate repeatability. Video documentation can be helpful and can be used to monitor progression or improvement in clinical signs. Neurological examination is a necessary and vital skill to have when working with horses. Remember to take your time and be safe when performing an evaluation, it is never worth risking bodily harm to assess a neurologic patient.

References Blythe, Linda L. Neurologic Examination of the Horse, Veterinary Clinics of North America: Equine Practice, Volume 3, Issue 2, 1987, Pages 255-281, https://doi.org/10.1016/S0749-0739(17)30672-7.

Furr M, Reed S. Neurologic examination. In: Furr M, Reed S, eds. Equine neurology. Ames, IA: Blackwell, 2008; 65–76.

Hahn, Caroline. Vet Clin Equine 38 (2022) 155–169. 2022 Elsevier Inc. https://doi.org/10.1016/j.cveq.2022.05.001

Johnson, Amy L. “How to Perform a Complete Neurologic Examination in the Field and Identify Abnormalities.” Neurology/Ophthalmology. AAEP PROCEEDINGS. Vol. 56 p. 331-337. 2010 https://aaep.org/sites/default/files/issues/proceedings-10proceedings-z9100110000331.pdf.

Mayhew IGJ. Large animal neurology. Ames, IA: Wiley Blackwell, 2009;11–46.

Young, Amy. “Neurological Examination in the Horse” Horse Report. Center for Equine Health – School of Veterinary Medicine, University of California, Davis. 1 November 2021. https://compneuro.vetmed.ucdavis.edu/sites/g/files/dgvnsk5376/files/inlinefiles/equine_neuro_exam_0.pdf. Accessed 6 Dec 2022.