Clinical and densitometric efficacy of the association of interferon alpha and pamidronate in the treatment of osteoporosis in patients with systemic mastocytosis

Osteoporosis accompanying severe mastocytosis leads to numerous compressed vertebrae. We treated four patients (mean age 52 years) with severe osteoporosis and mastocytosis proven by bone marrow biopsy (more than 40 mast cells/mm³), according to the following protocol: interferon alpha (IFN) 3 million units (MU) three times a week, reduced to 1.5 MU three times a week in the event of intolerance, and pamidronate (Pam) 90 mg/month in infusion. This treatment was given for 2 years. It was followed by Pam alone at a dose of 90 mg/month. After 3 or 4 years of treatment, no patient presented new vertebral or extravertebral fractures. The mean increase in bone mineral density (BMD) with IFN and Pam was 16.05±6.12% at the spine, 5±2.24% at the femoral neck, and 4.12±3.03% for the whole body; the increase or loss of BMD with Pam alone was +0.2±2.13% at the spine, −2.25±2.78% at the femoral neck, and −0.1±3.35% for the whole body. In one patient, the IFN dose was halved because of a flu-like syndrome, and in another IFN was discontinued at one year for the same reason. The association of IFN and Pam led to a major increase in bone marrow density in osteoporosis with concomitant mastocytosis and this gain was then maintained by monthly infusions of Pam.