ABNORMAL SKELETAL DEVELOPMENT IN GOATS WITH CONGENITAL HYPOTHYROIDISM

In some infants with congenital hypothyroidism (CH) X-ray photographs of the long bones reveal increased mineral content and absence of the medullary cavity, resembling osteopetrosis. We studied this feature in goats with goitrous CH, resulting from a familial defect in the structure of thyroglobulin. Thirteen goitrous animals and 6 normal controls, 0-9 months old, were used. Decalcified routinely stained sections of the proximal femur were used for histological and histomorphometric study. Thick (100 μm) undecalcified transvere sections of the femoral midshaft were used for microradiographic investigation. In the CH-animals reconstruction of bone tissue was reduced: In normal young goats 48.7 ± 6.2 (SD)% of trabecular surfaces were covered by active osteoblasts and 5.7 ± 1.7% by osteoclasts. In the goitrous goats these figures were resp. 22.8 ± 13.5% and 2.1 ± 1.8% (p < 0.05). In the most severely affected animals calcified cartilage and primary bone persisted, almost obliterating the marrow cavity; resorption of metaphyseal trabeculae was virtually non-existent. The diameters of the diaphysis and the medullary cavity varied widely due to growth of the goats, but they were no different in the 2 groups. It is concluded that in CH the condition resembling osteopetrosis results from severely delayed resorption of primary cartilage and bone, and normal development of cortical bone.