A case of primary hypothyroidism causing central nervous system atherosclerosis in a dog.

A 2-year-old, castrated male, Australian shepherd was presented with a history of chronic mild ataxia, obesity, and lethargy. The dog was treated with levothyroxine, but the ataxia worsened. Cranial nerve abnormalities developed and the dog was euthanized. Postmortem examination revealed marked thyroid gland atrophy and widespread, severe central nervous system atherosclerosis.