Linda L. Blythe

Otitis Media and Interna and Temporohyoid Osteoarthropathy

Otitis media/interna in the equine most commonly is a chronic, insidious infection with the unique sequella of temporohyoid osteoarthropathy in some horses. Head shaking may be the only clinical sign of the early stages of this disease. The arthritic condition often leads to fusion of the temporohyoid joint with resultant stress fractures of the petrous temporal bone. When this occurs, the horse presents as an acute neurologic case with clinical signs of vestibular and facial nerve dysfunction. Diagnosis, treatment, and prognosis are discussed. Recognition of this syndrome is important because many of these horses can be treated successfully and can return to normal function.

Prophylactic partial stylohyoidostectomy for horses with osteoarthropathy of the temporohyoid joint

Summary A technique of partial, unilateral, stylohyoidostectomy was developed for use in horses with chronic proliferative temporohyoid osteoarthrosis and ankylosis to prevent stress fractures of the skull. Partial stylohyoidostectomy may prevent fracture by eliminating forces on the skull resulting from movement of the tongue and larynx. Clinical, radiographic and histologic effects of unilateral (n=4) and bilateral (n=1) partial ostectomy performed in 5 horses were evaluated. Dysphagia was present for 1 week following unilateral, partial ostectomy but the horse that had a bilateral, partial ostectomy had residual prehension and mastication deficits when it was euthanatized 5 weeks after surgery. A pseudoarthrosis occurred between the cut ends of the stylohyoid bone. Unilateral, partial stylohyoidostectomy was easily performed and caused no permanent complications.

Sodium cyanate alters glutathione homeostasis in rodent brain: relationship to neurodegenerative diseases in protein-deficient malnourished populations in Africa

Sodium cyanate, a neurotoxic chemical in rodents, primates and humans, is implicated in neurodegenerative disorders in protein-deficient populations subsisting in parts of Africa on the cyanogenic plant cassava. The molecular and cellular mechanisms of cyanate neurotoxicity are not understood. This study investigates the effect of sodium cyanate on glutathione (GSH) homeostasis in rodent brain and liver in vitro and in vivo. GSH levels in mouse brain were rapidly, time- and dose-dependently decreased following intraperitoneal administration of 100, 200 or 300 mg/kg sodium cyanate. By contrast, GSH disulfide (GSSG) levels were increased and GSH/GSSG ratios were decreased in a dose-dependent manner in rat brain. Sodium cyanate depleted GSH levels in all regions of mouse brain. Brain glutathione reductase activity was dose-dependently inhibited, while glutathione peroxidase activity was not affected by sodium cyanate. The disruption of GSH homeotasis, as evidenced by reduced tissue GSH/GSSG ratios, likely results from cyanate-induced inhibition of glutathione reductase activity. The results of this study suggest that cyanate neurotoxicity, and perhaps cassava-associated neurodegenerative diseases, are mediated in part by disruption of glutathione homeostasis in neural tissue.

Neurologic Examination of the Horse

Methodology for the neurologic examination in the equine species is described. Information is organized to assist the reader in defining neurologic deficits and in localizing lesions to the major subdivisions within the central or peripheral nervous system. Numerous examples of deficits are presented to assist the reader in recognition of common neurologic disease states.

Dietary deficiency of cystine and methionine in rats alters thiol homeostasis required for cyanide detoxification

Nutritional status is an important factor in modulating the metabolic fate of xenobiotics. Sulfur amino acid (SAA) deficiency has been proposed as a risk factor for human neurological diseases among protein-poor populations subsisting on the cyanophoric plant cassava. Female Sprague-Dawley rats were used to develop and define a model of SAA deficiency for use in future studies examining cassava-related neurotoxicity. Rats were kept in metabolic cages for 7-21 d and fed a balanced diet (BD) of known composition or a comparable diet selectively deficient in methionine and cystine (SAA-free diet). Animals fed the SAA-free diet failed to thrive, lost body weight, excreted porphyrinic materials, and showed a steep and persistent reduction of urinary inorganic sulfate. In contrast, animals on the BD gained body weight and maintained baseline output of urinary inorganic sulfate. Urinary thiocyanate excretion did not differ between groups, but plasma thiocyanate concentrations reached double that in SAA-deficient rats. Increased plasma thiocyanate suggests mobilization of sulfur amino acids from endogenous sources. Liver glutathione and blood cyanide concentrations were similar in animals on the BD and the SAA-deficient diet. In summary, a diet free of methionine and cystine results in increased retention of inorganic sulfur as thiocyanate and a near absence of inorganic sulfur excretion in urine.

Cervical dorsal spondylosis with spinal cord compression in a black swan (Cygnus atratus).

Cervical dorsal spondylosis with spinal cord compression in a black swan (Cygnus atratus) was confirmed radiographically and morphologically. Clinically ataxia was associated. Noninflammatory, degenerative changes of the synovial joint cartilage were associated with the spondylosis.

Neuroanatomy and Neurological Examination

Components of the equine nervous system are described including classical anatomy and newer sensory innervation maps that are useful for localizing lesions to and within the nervous system. The key components in a neurological examination that help differentiate primary neurologic disease from musculoskeletal disorders are explained. Gait deficits associated with neurologic dysfunction are listed as well as diagnostic aids and an overview of differential diagnoses.