Calcium metabolism in paravertebral ligamentous ossification.

Twenty-eight patients with paravertebral ligamentous ossification (PVLO) and 11 control subjects were studied in an attempt to examine possible involvement of disturbances in mineral metabolism in the development of PVLO. No significant difference in baseline serum calcium and fasting urinary calcium excretion was found between patients with PVLO and controls. Patients with PVLO showed lower serum inorganic phosphate (Pi) and tubular reabsorptive capacity for Pi (TmP/GFR) than controls. Basal nephrogenous cyclic 3',5'-AMP (NcAMP) was elevated in some patients with PVLO. A significant inverse relationship was found between basal TmP/GFR and NcAMP in patients with PVLO (r = -0.50; P less than 0.01). Compared with controls, patients with PVLO had significantly lower calciuric responses to an oral calcium load (P less than 0.05), suggesting decreased intestinal calcium absorption. Furthermore, a significant inverse correlation was found between basal NcAMP and the calciuric response in patients with PVLO (r = -0.42; P less than 0.05). Serum 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25(OH)2D) levels were not significantly different between the two groups. The size of ossified areas in paravertebral ligaments estimated from spinal radiograms inversely correlated with the calciuric response to the oral calcium load (r = -0.50; P less than 0.01). These data demonstrate that the development of PVLO is associated with decreased intestinal calcium absorption in the face of normal serum 1,25(OH)2D level. Thus, together with previous observations showing a high incidence of PVLO in patients with hypoparathyroidism or familial hypophosphataemic rickets/osteomalacia, the present results suggest that the defect in the action of 1,25(OH)2D may underlie the development of PVLO.