OSTEOID MINERALIZATION DEFECT IN PRIMARY HYPERPARATHYROIDISM

Using a quantitative histological technique, four unselected patients with primary hyperparathyroidism were investigated and all were found to have a delayed or defective mineralization of osteoid, although their diet contained an adequate amount of vitamin D. This abnormality was most marked in the one patient with radiological bone disease. Mineralization of osteoid occurred during subsequent vitamin D administration, together with an improvement in ⁴⁵Ca absorption by the gut; osteoclast numbers and serum acid phosphatase levels also increased. We suggest that (1) endogenous vitamin D deficiency and hyperparathyroidism frequently co-exist, (2) vitamin D metabolism is abnormal in hyperparathyroidism, and (3) radiological loss of bone density and erosions in hyperparathyroidism are due to impairment of the process of bone repair, i.e. there is defective mineralization of the osteoid which is laid down by osteoblasts to fill the resorption lacunae.