Your horse has misstepped while in the ring, it seems to drag its right rear toe.  It stumbled a couple of times on the last trail with no good reasons.  You are concerned: is it a problem with a joint, a muscle or is it neuro? The goal of the presentation is to help you recognize some of the more subtle signs and take you through the multiple steps of the neurological examination.  At the end we will review some of the neurological diseases that can affect Alberta horses.

Sorting out the neurologic signs and localizing the lesion are the first steps that your veterinarian will try to accomplish.  Are there seizures, a change of behavior? Does the horse show a head tilt?  Is it just the gait that is abnormal? The process begins with gathering information on the horse (age, Breed, occupation), history (when did the stumbling start, how did it progress, did the horse fall?).  The veterinarian will perform a physical examination looking for other signs that may help in localisation of the lesion (asymmetry of muscles, movement of the neck).  Step 3 is the neurological examination per se with the goal of determining as best as possible the site(s) within the nervous system. Localization of the lesion(s) is important for the clinician to determine the most likely diagnosis, determine the best tests, provide a rational treatment and discuss prognosis and preventative measures for the rest of the horses if necessary.

The neurologic evaluation usually starts with a general assessment of the mental status and the behavior of the horse. Then the veterinarian will test the cranial nerves and some of the reflexes on the neck and the thorax.  The next step is the evaluation of the gait of the horse.  This will be done when the horse is walking, trotting, when the horse is lunged or with the rider in the saddle. This part of the examination is usually critical in the evaluation of diseases affecting the spinal cord.  To localize the lesion, three questions must be answered:
1. What limb(s) is (are) affected?
2. What kind of deficit
3. To what degree?

The types of deficit observed are:
- Ataxia or proprioceptive deficit is characterized by poor coordination when moving the limbs and body. It is seen as swaying of the pelvis and trunk, crossing of the limbs, inconsistent placement of the feet when moving or circling (e.g. sometimes close to the midline, sometimes wide) and stepping on the opposite foot.
- Weakness or paresis is seen as knuckling, stumbling or dragging of the limb. Often times, the paretic limb has worn hooves and when the animal bears weight on the limb, it will tremble and/or buckle.
- Spasticity is characterized by stiff movement of the limbs and little flexion.
- Dysmetria is characterized by an increase (hypermetria) or decreased (hypometria) joint flexion.

The grading or severity of the deficit is somewhat subjective, however, if a grade 0 is no abnormality and a grade 4 (some literature include a 5th degree) is so severe that the horse falls on its own, then a grade 2 is a deficit that one can pick up at the walk or the trot, a grade 3 is obvious and a grade 1 is a deficit that is not apparent at normal gait but is observed during more complicated maneuvers or “special” tests.
Special tests

Tail Pulling (sway test)
A normal response is for the horse to resist to the pull and allow only a slight deviation of the pelvis in the direction of pulling. Weak horses are easily pulled to the side, and take a few more strides to return to their normal gait.

Backing Up
The healthy horse will back up the same way it walks. When the head is elevated the healthy horse will show a wider base in the back but the placement remains approximately the same at each step, whereas the ataxic horse will inconsistently be wide or narrow.

Tight circling is most helpful in assessing proprioception. Helpful information is gained by comparing one side to the other. When circling a horse, the outside front limb crosses in front of the inside limb. It is the opposite in the rear limbs. Circumduction or excessive abduction of the limb (mainly in visible in the outside rear limb), pivoting around the inside limb, not crossing over, hitting one foot with the other are considered abnormal.

Walking in Zig-Zags
This test gives information similar to that obtained with the tight circling

Walking up and down a slope
This test is helpful in detecting weakness particularly of the rear limbs, ataxia and spasticity. Weak horses will stumble or knuckle at the fetlock. Ataxic horses may hit one limb with the other, some may pace even if it is not their natural gait. Spasticity is usually more pronounced. Again, lifting the head up will exacerbate signs.

By the end of this examination, the veterinarian should know whether the horse’s problem is neurologic or not and if so what areas of the nervous system is involved.  There may not be enough information yet to make a final diagnosis but your veterinarian may have enough information to make a list of possible diagnoses and choose the most appropriate tests to confirm or rule out the diagnoses on that list.