Hypercalcemia in idiopathic myelofibrosis: modulation of calcium and collagen homeostasis by 1,25-dihydroxyvitamin D3.

A case of idiopathic myelofibrosis (IMF) presenting with hypercalcemia and hypercalcitriolemia is reported. It is proposed that ectopic production of the active vitamin D metabolite related to ongoing clonal expansion in the bone marrow accounts for the hypercalcemic state. Consistently low levels of circulating type I procollagen propeptide (PICP) and lack of progression of the bone marrow fibrosis during almost 6 months of follow-up point to an in vivo inhibition of type I collagen synthesis by 1,25-dihydroxyvitamin D3.