[Severe therapy refractive osteoporosis : A rare differential diagnosis].

Systemic mastocytosis is defined as a clonal increase of mast cells. We report on four patients with severe osteoporosis and histologically confirmed systemic mastocytosis. In spite of antiresorptive therapy the patients developed further vertebral fractures and suffered from ostealgia. Systemic mastocytosis is an important differential diagnosis in patients with therapy refractive and unexplained osteoporosis. Skin involvement (urticaria pigmentosa) is a rare occurrence and in most cases an isolated involvement of bone marrow is present. Determination of serum tryptase can provide indications for systemic mastocytosis but the diagnosis is only confirmed by bone marrow biopsy. There is a high risk of vertebral fractures and patients should be treated in specialized centers. Zoledronic acid can be a therapeutic option for indolent osteoporosis associated with systemic mastocytosis.