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Systemic mastocytosis: a diagnostic challenge.

We present an unusual case of adult-onset systemic mastocytosis with biopsy-proven skin and bone manifestations with the rare presentation of lumbar fracture and osteopenia. The normal 24-hour urine histamine is surprising in this patient, but it does not rule out mastocytosis. It is a sensitive assay that can give false negative results if stored before the assay is performed. Also histamine and PGD2 metabolites are more sensitive and specific. It is surprising that our patient did not have gastrointestinal symptoms. In one prospective study of 16 patients with systemic mastocytosis in which 75% had bone marrow involvement as the most common extracutaneous site, 80% were found to have gastrointestinal symptomatology, indicating such symptoms to be more common than previously thought. The lack of pruritus is also surprising, as most cutaneous lesions of urticaria pigmentosa are pruritic. Symptoms of systemic mastocytosis, particularly pruritus may respond to antihistamines and the bone disease may not respond to calcium and hormone manipulation. The main role of the latter is to prevent further bone loss. We may consider the use of cromolyn or ketotifen if she does not respond. Close follow-up will be needed to check for progression, however she appears to have a good prognosis with skin involvement and no hematologic abnormalities.