Utsugi S, Saito M, Shelton GD.
An 8 yr old male golden retriever was evaluated because of chronic, progressive, multiple neurologic signs. Physical examination showed marked obesity and facial swelling with a “tragic facial expression.” Neurologic evaluation revealed the dog had multiple cranial nerve deficits and lower motor neuron signs in the pelvic limbs. Serum biochemical analysis and thyroid function tests were consistent with hypothyroidism. A biopsy from the common peroneal nerve revealed a loss of myelinated fibers, inappropriately thin myelinated fibers, and resolving subperineurial edema. The diagnosis of polyneuropathy associated with hypothyroidism was made. Levothyroxine therapy was initiated. Response to levothyroxine treatment was slow, with most neurologic abnormalities persisting for >6 wk. However, the dog made a full neurologic recovery within 6 mo. Although the occurrence of polyneuropathy in dogs resulting from hypothyroidism has been controversial, the study authors demonstrated that hypothyroid polyneuropathy can occur in dogs as documented in humans. This is the first report describing long-term follow-up information together with detailed pathological features of hypothyroid polyneuropathy in a dog. In hypothyroid polyneuropathy, the response to thyroid replacement may be slow, but a recovery can be expected if treatment is initiated before peripheral nerve fiber loss becomes severe.