Diagnosis of canine hypothyroidism: some clinical and laboratory methods

By detailed history taking and physical examination, 299 dogs, selected from the Clinic case-load, were placed in groups consisting of 47 cases of suspected hypothyroid¬ ism, (HS), 47 of other hormonal disease (OH), 99 of pyoderma (P), 57 of allergic dermatoses (A) and 49 of suspected ectoparasitism (EP) . Groups P, A and EP were confirmed to be such by bacteriological and parasitological examinations and the presence of circumstances indicative of dermal allergy. For comparison, 68 normal dogs were available. There were statistically significant clinical differences between Groups HS and OH, the two most likely to afford difficulty in clinical differential diagnosis, in the incidence of alopecia, lethargy and above normal weight. Combinations of these were also much more frequent in Group HS. Other clinical features, especially of the skin, were sufficiently different in quality as well as numerically to separate all groups from Group HS.

Skin thickening is well known in hypothyroidism but the groin was the only one of 15 sites with significantly thicker skin in Groups HS and OH than the other groups. The difference was not due to breed influence which was, however, greater than that of hypothyroidism on the phase of hair growth. Twice as many HS dogs as others had subclinical anaemia but time incidence was lew

The occurrence of a breed incidence in hypothyroid!am was confirmed. Dogs of larger breeds were not the more frequently affected. In Group HS, females were; significantly more numerous than males and showed the first signs when younger. Proportionately more older animals were affected and neutered animals were at greater risk than entire animals.

than entire animals. Circulating cholesterol, protein bound iodine (PBI), serum glutamic oxalacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), serum alkaline phosphatase (SAP), Cortisol, thyroxine (T4) and triiodothyronine (T3) were assayed. Cholesterol, T4 and T3 concentrations were unaffected by time of day and post-prandial interval but household scraps added to the diet raised cholesterol levels. Cholesterol, levels were significantly higher in Group HS. Liver damage was indicated by high SAP values in untreated dogs of Group HS and OH dogs. Cortisol level response to adrenocorticotrophic hormone (ACTH) stimulation helped to identify cases of hyperadrenocorticalism as did skin biopsy histology. Sertoli cell tumours were confirmed histologically.

T4 and T3 levels differed significantly between some groups but did not partition Group HS from all others. Subnormal levels were present in same dogs of all groups. More precise partition of euthyroid fron hypothyroid dogs, using in vitro methods only, would require additional tests such as thyroid stimulating hormone (T5K) assay or the response to TSH stimulation.

ponse to TSH stimulation. The relationship of breed, age and sex to 'base-line' levels of thyroid hormone and the possibility of (ncn-clinical) biochemical hypothyroidism predisposing to pyoderma require further investigation.