A 52-year-old female patient is described. The patient was referred to a dermatologist with a two-year history of lesions on her head and neck. She was noted to have red brown, non-scaly, slightly infiltrative papules with a positive Darier's sign, which was biopsy proven to be cutaneous mastocytosis. Further workup showed a markedly elevated serum tryptase levels (58.9 micrograms/L). She denied any abdominal pain, diarrhea, flushing, severe allergic reactions or any other systemic symptoms. In order to rule out systemic mastocytosis a bone marrow biopsy was requested. The CBC and the peripheral smear were unremarkable. A dilute bone marrow aspirate showed normal trilinear hematopoiesis and no evidence of increased myeloblasts or mast cells (Figure 1, panel A). A trephine biopsy showed nodular and paratrabecular mast cell lesions admixed with lymphocytes (Figure 1, panels B and C). Specifically both CD3+ T and CD20 + B-lymphocytes are admixed with the mast cell aggregates (Figure 1, panels D and E). CD34 showed no increase in myeloblasts (Figure 1, panel F). CD117 and tryptase confirmed large mast cell aggregates in the lesions seen on H&E (Figure 1, panels G–I). Quantitative PCR analysis identified the D816V mutation in the KIT gene and with no B or C symptoms the diagnosis of indolent systemic mastocytosis was reached.1 The patient is periodically monitored with imaging, CBCs and serum tryptase levels.

Figure 1.

Bone marrow aspirate and trephine biopsy show the infiltration of a CD117 and tryptase positive mast cell infiltrate admixed with lymphocytes.

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