Metabolic Disorders of the Peripheral Nerve and Neuromuscular Junction
This uncommon complication of diabetes mellitus (see Diabetes Mellitus) is seen in cats and rarely dogs. Signs include weakness, ataxia, and muscle atrophy. Affected cats often have unilateral or bilateral tibial nerve dysfunction, evident as a plantigrade stance. There are several proposed pathophysiologic mechanisms, but prolonged hyperglycemia seems to be the important underlying factor. Pathologic findings in nerves consist of demyelination with remyelination, axonal degeneration, or both. Diagnosis is based on clinical findings, laboratory evidence of diabetes mellitus, and nerve biopsy. The prognosis is guarded, but partial or complete recovery can occur with insulin therapy.
This neuropathy is a potential complication of hypothyroidism in dogs (see Hypothyroidism). Mature dogs, especially large-breed dogs, are predisposed. Several syndromes have been reported, including tetraparesis with proprioceptive deficits and hyporeflexia, vestibular dysfunction, megaesophagus, and laryngeal paralysis. In some cases, classic signs of hypothyroidism (eg, obesity and dermatopathy) are absent, and neurologic dysfunction is the only sign of illness. Pathologic findings in peripheral nerves consist of demyelination or remyelination and axonal degeneration. The pathophysiology is poorly understood and, in some affected dogs with motor deficits, a myopathy may also be present. Diagnosis is based on clinical features, laboratory assessment of thyroid function, and response to thyroid supplementation. In some, but not all, cases, signs resolve within several months of starting thyroid replacement therapy.