The effect of vitamin D status on the severity of bone disease and on the other features of primary hyperparathyroidism (pHPT) in a vitamin D deficient region.

A clear relationship between vitamin D status and the clinical indices of primary hyperparathyroidism (pHPT) severity has not been convincingly established. We proposed that such a relationship might exist, in so far as vitamin D deficiency could contribute to the severity of metabolic bone disease and promote the growth of the parathyroid tumor. Accordingly, we undertook a retrospective study and analyzed the clinical, biochemical, radiological and histopathological findings in a group of 49 patients who underwent parathyroidectomy at our center. Patients who had skeletal X-rays were grouped, according to their X-ray findings, in group A (19 patients; 45%) if they had severe bone changes, or group B (23 patients; 55%) if they had mild or no bone changes. Patients were also stratified according to their 25-hydroxyvitamin D (25-OHD) levels in tertiles. The 2 groups were compared using Fisher's exact test or analysis of variance as appropriate. Group A patients were younger (p=0.001), had more musculoskeletal symptoms (p=0.0003), and complained more frequently of fatigue (p=0.02). They had higher alkaline phosphatase (AP; p=0.0002), PTH index (p=0.0007), and serum Ca level (p=0.006). There were more patients from the lower and middle vitamin D tertiles and fewer patients from the upper vitamin D tertile in group A (p=0.02). Post-operative severe hypo-calcemia was more prevalent in group A patients (p<0.0001). Resected parathyroid tumors were larger in size in group A patients (p=0.01), and weighed more (p=0.01). There was a positive correlation between the weight of the parathyroid tumor and the PTH index (p=0.002), and AP level (p=0.0007). We concluded that vitamin D deficiency is a contributing factor to both the severity of bone disease and the high activity of parathyroid tumors seen in many patients with pHPT in vitamin D deficient regions.