Thyroid gland and arterial lesions of Beagles with familial hypothyroidism and hyperlipoproteinemia.

Primary hypothyroidism with marked hyperlipoproteinemia and modest to severe atherosclerosis was described in a family of Beagles. The disease was familial and probably hereditary, but the mode of inheritance was unknown. Signs of the disease occurred as early as 1.5 years of age and as late as 5 years of age. The onset of the disease was heralded by reduced concentrations of serum thyroxine, increased binding capacity of thyroxine-binding globulin, and reduced response to injected thyroxine-stimulating hormone. Thereafter, serum lipids, particularly serum cholesterol, increased markedly even though the dogs consumed a diet low in fats and cholesterol. Thyroxine administration resulted in a precipitous decline in serum cholesterol concentrations. Microscopic changes in the thyroid glands included neoplastic transformation, adenomatous hyperplasia, lymphocytic thyroiditis, and atrophy. Moderate to severe atherosclerosis occurred mainly in the coronary and renal arteries. Atherosclerotic arteries were stenotic but patent, and there was no evidence of prior occlusion or thrombosis.