Bone marrow findings in adult patients with urticaria pigmentosa

In order to better assess the prognosis of adult patients with urticaria pigmentosa, 35 patients with generalized maculopapular skin lesions and biopsy-proved cutaneous mast cell increase had light and electron microscopic examinations of their bone marrow; 46% had an increased mast cell content that was focal in all but four patients. Additional frequent findings in this group were an increased cellularity, nuclear-cytoplasmic dissociation of maturation, eosinophilia, and macrophages that contained ingested nuclei. Similar changes were found in far fewer patients without increased marrow mast cells. Only one patient with massive cutaneous mastocytosis had mast cells with relatively large nuclei and immature granules in the extensively involved marrow. Repeated biopsies in this and in six other patients over 3 years showed no worsening of the marrow findings, and the clinical course of all patients was stable over up to 10 years of follow-up. The variable findings in the patients suggest that mastocytosis with cutaneous involvement is a heterogeneous disease where diverse stimuli may cause an increase of mast cells. The clinical course is, however, relatively stable.