O significado dos achados histopatológicos no diagnóstico do hipotireoidismo em cães, com ênfase nas alterações dos músculos piloeretores

Abstract

Given that the frequency of hypothyroidism in dogs in Brazil is high and that laboratory exams are, many times, inconclusive, the establishment of the real significance of hypertrophy of piloerector muscles could be important for pathologists. This study aimed at determining if there is a correlation between the hypertrophy of these muscles and low levels of thyroid hormones in dogs, assessing the diagnostic significance in case of a positive correlation, and describing the general clinical and dermato-histopathological findings in dogs with hypothyroidism in Brazil. Two hundred dogs from both sexes aged between 6 months and 18 years of age and with skin disease suspected to be related to hypothyroidism were evaluated at the Dermatology Section of the Veterinary Hospital for Small Animals of Universidade Federal Rural do Rio de Janeiro between November 2001 and October 2002. Cutaneous biopsies for morphometry of the piloerector muscles, hormone dosing, skin scrapings, trichograms and cytology exams were performed. Dogs between 2 and 4 years of age were the most affected. The disease affected more females (61%) than males (38.9%). Animals from 32 breeds, especially Poodle, Cocker Spaniel and German Shepherd, with the exception of crossbreeds, were affected. Lethargy, obesity and reproductive disorders were observed among the general clinical alterations. Cutaneous alterations such as hypotrichosis, alopecia, dull and brittle coat, pruritus, seborrhea and hyperpigmentation were frequent. Hypopigmentation, skin thickening and facial myxedema were also seen. Concomitant diseases and/or lesions such as otitis, secondary pyoderma and allergic dermatitis were frequently seen. The histopathological exam revealed the presence of acanthosis, hyperkeratosis, follicular alterations – mainly follicles in the telogen phase, hypertrophy (70.5%) and tumefaction (cervical – 53.8% and lumbar – 89.4%) of piloerector muscles. The measurements obtained for longitudinal sections of piloerector muscles of the cervical region were: larger diameter D=609.49μm; smaller diameter d=90.08μm; area (A)=65640,84μm2; metric index (m.i.)= 0,1799. In the lumbar region, the same evaluations showed the following results: D= 1389.4μm; d=450.98μm; A=191285,2μm2 and m.i.= 0,1734. For transverse sections the results for the cervical region were D=195.80μm; d= 117.09μm; A=28354,9μm2 and m.i.= 0,6277, while for the lumbar region they were D=221.75μm; d= 135.29μm; A=35605,2μm2 and m.i.= 0,6261. There is no doubt that the alterations of the piloerector muscles (hypertrophy and eosinophilic vacuolation) are important for the diagnosis of hypothyroidism; however, the association of these alterations with other histological findings such as dermal thickness, trichilemmal keratinization, predominance of atrophic follicles and follicles in the telogen phase makes the histopathological exam even more helpful for the diagnosis of hypothyoroidism.