Joe Mayhew

Large Animal Neurology


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seizures), blindness, and lethargy. Although often sluggish in movement, little or no alteration in gait occurs, at least in the subacute to chronic stages. Central motor pathways to and sensory inputs from cranial nerves can be disrupted, and such syndromes are discussed under the individual cranial nerve disorders. Particularly with metabolic diseases such as hyperammonemia, and with those focal and diffuse disorders accompanied by inflammatory lesions or by perilesional edema, there can be dramatic fluctuations in the severity of behavioral signs displayed over periods ranging from minutes to weeks. This can even mean that there are no overt signs demonstrated at a point in time, and within a few hours there may be prominent behavioral changes and even an uncontrollable patient.

Photo depicts self-inflicted lesions caused by biting are quite unusual and can be spectacular with horses suffering from the self-mutilation syndrome.

      A period of calm or of induced sedation may be taken as an opportunity to search for localizing signs of brain disease that are often overshadowed by any accompanying wildly aberrant behavior. These will include subtle signs such as asymmetric menace responses, anisocoria, asymmetric nasal sensation, head tilt, head turn, facial hypotonia, and drifting to one side walking undirected with blindfold applied.

      Faced with an animal showing aggressive or violent behavior, for safety reasons the clinician must consider sedating the patient. Most times diazepam will not be at hand but expedient IM or IV administration of moderate to high doses of a readily available α‐2 agonist drug combined with a synthetic opioid drug is perfectly satisfactory in most circumstances. Obviously, with a patient from a rabies‐endemic area, this diagnosis must be considered of paramount importance. Some diseases that result in such a fulminant syndrome of wildly abnormal behavior can have a positive outcome, and therefore euthanasia must be given careful consideration while sedation takes effect. Examples of those diseases with a more favorable prognosis include thiamine‐responsive polioencephalomalacia, hypoadrenocorticism,1 neonatal hypoxic and ischemic encephalopathy, salt poisoning, hypomagnesemia, hypocalcemia, hypoglycemia, hepatic, exogenous and intestinal ammonia intoxication, ketosis, metaldehyde toxicosis, macrocyclic lactone overdose, and immediate post‐head trauma delirium.

Photo depicts a milking Friesian cow likely was suffering from ketosis with episodes of bizarre behavior characterized by vigorously attacking animate and especially inanimate objects such as the metal bars of her pen as shown; she recovered fully with treatment. Photo depicts painful processes, perhaps especially abdominal pain, frequently cause unexpected and abnormal behavior in large animals frequently, and such actions need to be distinguished from those caused by morbid neurologic diseases. Photo depicts the Thoroughbred racehorse. Photo depicts horses diagnosed as headshakers usually have little else in the way of physical and neurologic signs. Photo depicts radiographs of the atlantooccipital region of a horse demonstrating headshaking.