Lymphocytic Adenohypophysitis and Adrenalitis in a Dog With Adrenal and Thyroid Atrophy

A 4.5-year-old spayed female Great Pyrenees with hypothyroidism and hypoadrenocorticism had a slightly enlarged pituitary gland and bilaterally atrophic adrenal and thyroid glands. Lymphocytic adenohypophysitis and adrenalitis were found in which B lymphocytes and plasma cells dominated the adenohypophysitis but T cells dominated the adrenalitis. The thyroid gland had extensive follicular atrophy and collapse. The combination of primary hypothyroidism and hypoadrenocorticism resembles type II autoimmune polyendocrine syndrome or Schmidt syndrome in humans. Adenohypophysitis is rare in dogs and not reported in polyendocrine disease in animals.