Large Animal Neurology. Joe Mayhew

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Figure 5.8 Radiographs of the atlantooccipital region of a horse demonstrating headshaking. There is marked modeling of the caudal aspect of the occipital protuberance (arrows). This riding horse would only perform persistent dorsoventral head movements while fully tacked‐up with a bridle for ridden work. Local anesthetic solution deposited around the region of bone modeling almost stopped the syndrome occurring for about an hour, and infiltrating a repository glucocorticoid drug in the region attenuated the syndrome markedly for over a week. Ultimately, surgical exploration and removal of much of the new mineralized tissue was undertaken, and after healing of the surgical site the syndrome did not occur while the horse was ridden for several months before the case was lost to follow‐up. It is however worth recalling that horses without the problem of headshaking can have various radiographic changes present in this region (see Figure 3.9).

      Quite bizarre syndromes can be seen as idiosyncratic reactions to intramuscular injections of depot forms of antipsychotic drugs including fluphenazine used for chronic sedation and sulpiride used for lactation induction protocol. Included in these can be episodes of unusual, monotonous movements of the limbs and of the head and neck with the thoracic limbs extended and the head touching the ground—even flexed between them in a “praying” posture.² Episodes of bradykinesia or freezing can also occur. Such signs can be interrupted by unpredictable, violent events that render the situation dangerous although most cases have responded to anticholinergic therapy with diphenhydramine and/or benztropine.³ These syndromes can be compared to the extrapyramidal side effects seen in people with antipsychotic and antidopaminergic drugs including fluphenazine and metoclopramide, but they can also occur in animals suffering from brain injury and from meningitis.

With no other neurologic signs, it can be difficult to be sure whether subtle behavioral syndromes are learned repetitive behavioral traits—or simply actions perceived as being unacceptable responses to human‐induced management restrictions placed on domestic animals rather than being due to acquired morbid neurologic lesions. Examples of these include repetitive licking and sucking (Figure 5.6), head shaking (Figures 5.7 and 5.8), tail wringing, aggressiveness, self‐mutilation, and refusing to follow learned instructions such as taking jumps. Some of these syndromes are discussed in Chapter 28, although for a more detailed evaluation of equine behavioral aberrations, the reader is directed to further literature.^4–15 Although tempting to speculate, there is not ample evidence that many forms of varied behavior, regarded as unacceptable in domesticated animals by humans, are genetic for the most part,¹⁶ and indeed many clinicians would rather suggest they are acquired, even when appearing in successive offspring.

      Finally, the potential role of painful sensory inflammatory or degenerative lesions such as ganglioneuritis¹⁷ in causing unacceptable and dangerous behavior needs further ratification.

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