Iatrogenic, sulfonamide-induced hypothyroid crisis in a Labrador Retriever.

This case report describes a sulfonamide-induced hypothyroid crisis in a 4-year-old Labrador Retriever bitch. Empirical therapy with high-dose trimethoprim-sulfamethoxazole for 10 days produced signs of weakness, ataxia and mental depression and the clinicopathological results supported hypothyroid-induced central nervous system depression. Short-term levothyroxine sodium therapy led to complete resolution of all clinical signs and follow-up thyroid hormone assays ruled out underlying thyroid pathology. This case report is the first to highlight this potentially life-threatening manifestation of sulfonamide-induced hypothyroidism. Sulfonamide combinations are widely used antimicrobials in veterinary medicine and early recognition of this syndrome is critical.

Improvement in myocardial dysfunction in a hypothyroid dog.

An 8-year-old, male, Alaskan malamute was evaluated for a 2-week history of lethargy, inappetence, and distended abdomen. The dog was diagnosed with severe hypothyroidism, exhibited facial myxedema and had myocardial dysfunction with ascites and pleural effusion. Myocardial function improved and facial myxedema and effusions resolved with levothyroxine supplementation.

Hypothyroidism and myxedema coma.

Hypothyroidism is a common endocrinopathy in dogs but is rare in cats. Lymphocytic thyroiditis and idiopathic thyroid atrophy are common causes of this condition. Specific thyroid function tests, in conjunction with clinical signs and physical examination findings, are used to help confirm a diagnosis of hypothyroidism. This disease can be managed with synthetic hormone supplementation and has an excellent prognosis. Myxedema coma is a rare and potentially fatal manifestation of severe hypothyroidism that can be successfully treated using intravenous levothyroxine.

Myxedema coma leading to respiratory depression in a dog.

A 10-year-old, intact male, cocker spaniel was presented with hypothermia, without shivering, and progressive stupor leading to coma. Myxedema coma, potentially precipitated by diuretic therapy, was tentatively diagnosed and treatment initiated, but progressive respiratory depression led to the decision to euthanize. Postmortem findings supported the diagnosis of myxedema coma.

Intravenous administration of levothyroxine for treatment of suspected myxedema coma complicated by severe hypothermia in a dog.

A 7-year-old male English Coonhound with suspected myxedema coma complicated by severe hypothermia and metabolic abnormalities was treated with a combination of active external and core rewarming techniques, i.v. and oral administration of levothyroxine, supplemental oxygen, and administration of fluids (0.9% NaCl solution). Myxedema coma develops as a consequence of severe hypothyroidism and is characterized by a hypometabolic, stuporous state. Myxedema coma is associated with a high mortality rate, and most reported cases have involved Doberman Pinschers. Intravenous administration of levothyroxine can be used successfully in combination with oral administration to restore normal metabolic function and assist in warming and thermoregulation, although dosages should be conservative to avoid adverse cardiovascular effects.

Histochemical study of cutaneous mucins in hypothyroid dogs.

A dermal mucinosis, visualized as dermal alcianophilic material, is occasionally present in canine hypothyroidism (myxedema). Various histochemical reactions (alcian blue/periodic acid-Schiff [PAS], alcian blue at pH 2.6, alcian blue at pH 1.0, critical electrolytical concentrations with and without dimethylsulfoxide, differential hydrolysis by hyaluronidases) were performed on skin biopsies from six dogs (four females and two males ranging from 8 to 13 years) affected by hypothyroidism, all of them presenting dermal mucinosis in hematoxylin and eosin-stained sections. In these dogs, the only polysaccharidic compound involved in the dermal mucinosis was hyaluronic acid. In this study, hyaluronic acid dermal deposits of hypothyroid dogs were significantly different from those of controls in subepidermal connective tissue and loose reticular connective tissue but not in periadnexal zones. We recommend the combined alcian blue/PAS reaction as a routine technique to assess dermal mucinosis in hypothyroid dogs.

Multifocal myxedema and mixed thyroid neoplasm in a dog.

An Old English Sheepdog developed multiple tumor-like masses bilaterally on the head, back, elbows, and hocks, and severe swelling of all digital pads. The gross lesions were the result of accumulation of myxedematous connective tissue in the dermis. Abundant glycosaminoglycan-rich ground substance was confirmed by colloidal iron, toluidine blue and alcian blue stains. The dog also had a mixed follicular-compact cellular carcinoma in the left thyroid gland. The right thyroid had a tumor composed of anaplastic mesenchymal cells forming myxomatous matrix and islands of abnormal cartilage closely integrated, and possibly contiguous, with a follicular-compact cellular carcinoma. The cellular atypism and numerous aberrant mitotic figures in the mesenchymal areas suggested malignancy, although pulmonary metastases derived only from the thyroid carcinoma. Clinically, the dog showed no signs of hypo- or hyperthyroidism, although a resting serum T-4 was slightly below normal.

Epidemiologic features of canine hypothyroidism.

This study investigates the epidemiologic features of 3,206 dogs diagnosed with hypothyroidism (including myxedema) from 1.1 million dogs seen at 15 veterinary teaching hospitals between March, 1964 and June, 1978. Nine breeds found to be at high-risk for hypothyroidism were: golden retrievers, Doberman pinschers, dachshunds, Shetland sheepdogs, Irish setters, Pomeranians, miniature schnauzers, cocker spaniels, and Airedales. Two breed with a significant deficit of risk were German shepherds and mixed breed (mongrel) dogs. Age risk was greatest among younger dogs of high-risk breeds, further suggesting a genetic component to the etiology of this disease. In contrast, low-risk dogs had increasing relative risk through nine years of age. Spayed female dogs displayed a significantly higher risk when compared to intact females. Though not statistically significant, male castrated dogs had 30% more hypothyroidism compared to their intact counterparts. Among the case series were 91 endocrine and hormone-related neoplasms and 198 other endocrine-related disorders. Further studies linking canine hypothyroidism to other conditions, particularly cancer, could provide valuable insight into human disease experience.