Juvenile hyperthyroidism in a dog

Hyperthyroidism is the most common endocrinopathy in cats, and most cases are caused by multinodular hyperplasia or follicular cell adenoma, although thyroid carcinomas occur infrequently. Hyperthyroidism is rare in dogs, and most cases are caused by functional thyroid carcinomas. There are case reports of canine hyperthyroidism secondary to exogenous sources, and rarely thyrotoxicosis can be seen with therapeutic doses of levothyroxine prescribed for hypothyroidism. A case of juvenile hyperthyroidism has been reported in a cat and a histopathological diagnosis of diffuse thyroid hyperplasia was made. This is the first reported case of functional eutopic thyroid tissue in a young dog. Histopathological examination reported bilateral hyperplastic change in the thyroid glands, similar to the case of feline juvenile hyperthyroidism.

c-myc Expression is associated with increased proliferation activity in thyroid follicular cells of Graves' disease as stimulated by autoantibodies

Kashima K, Yokoyama S, Daa T, Takahashi K, Nakayama I, Noguchi S. c-myc Expression is associated with increased proliferation activity in thyroid follicular cells of Graves' disease as stimulated by autoantibodies. Eur J Endocrinol 1996:135:69–76. ISSN 0804–4643 Expression on thyroid follicular cells of HLA-DR, c-myc protein and proliferating cell nuclear antigen (PCNA) was examined immunohistochemically in 28 cases of Graves' disease (GD) and in 29 cases of Hashimoto's thyroiditis (HT). Immunoreactivity for PCNA in GD was seen not only in follicular cells adjacent to a lymphocytic infiltration, where the follicular cells were positive for HLA-DR, but also in hyperplastic follicular cells without the infiltration. The distribution of expressed c-myc protein was similar to that of PCNA in GD but not in HT. Semiquantitatively graded degrees of lymphocytic infiltration and expression of HLA-DR, c-myc and PCNA in GD showed a high correlation with one another. However, the degrees of c-myc expression in HT showed no significant correlation with any other degrees. Intraperitoneal injection of bovine TSH or of immunoglobulins derived from a patient with GD in rabbits induced hyperplastic change of thyroid follicular cells, as reflected in PCNA and c-myc immunoreactivity, as well as strong peroxidase and acid phosphatase activity. Immunization with synthesized peptide of thyrotropin receptor also exhibited the same results in the rabbit thyroids. Our results indicate that c-myc expression on follicular cells of GD may reflect a stimulation by autoantibodies mediated through the thyrotropin receptor. Kenji Kashima, Department of Pathology, Oita Medical University, 1-1 Oita-gun, Oita 879-55, Japan

Responses to TRH, T3 suppression tests and histological findings by needle biopsy in patients with simple goitre in Japan

Studies were performed in 120 patients with simple goitre, defined as relatively soft diffuse goitre. All were clinically and biochemically euthyroid and their antithyroid antibodies were negative. The TRH test was performed in 115, and a T3 suppression test was performed in 99 after the TRH test, while satisfactory biopsies of the thyroid were obtained in 37. The results showed that 28 of the 115 cases (24%) had an abnormal response to TRH; 8 (7%) were hyporesponders and 20 (17%) were hyperresponders. The T3 suppression test showed that 3 of 99 cases (3%) were non-suppressible. As determined by histological examination of the needle biopsy specimen, 17 of the 37 cases (46%) had normal follicles without lymphocytic infiltration, 10 (27%) had diffuse chronic thyroiditis, 5 (14%) had focal thyroiditis and 4 (11%) had diffuse epithelial hyperplastic change, and 1 (3%) had an adenomatous goitre. It is suggested that simple goitre defined as above includes various thyroid diseases and that the results of TRH tests, antithyroid antibody estimations and histological findings do not correlate in many patients.