Lymph node findings in generalized mastocytosis.

Lymph nodes from 21 cases of generalized mastocytosis were studied histologically to confirm or exclude mast cell infiltration, and to investigate their micro-architecture. Mast cell infiltrates were detected in 17 (80%) of the lymph nodes and were found mainly in the medullary cords and sinuses. Diffuse infiltration was seen in 14 cases and focal infiltration in three cases. The following pathological findings were frequently observed: germinal centre hyperplasia (n = 14), which is probably a nonspecific finding; and hyperplasia of small blood vessels, which sometimes resembled high endothelial venules (14), eosinophilia (8), plasmacytosis (7) and collagen fibrosis (6), all of which may well be related to the effects of mediators released by mast cells. Infiltrates of acute or chronic myeloid leukaemia were seen in six lymph nodes. Division of the cases into two prognostically different groups, i.e. systemic mastocytosis, in which the skin lesions of urticaria pigmentosa are present and the prognosis is favourable, and malignant mastocytosis, in which there is no cutaneous involvement and the prognosis is poor, revealed that all six lymph nodes exhibiting leukaemic infiltrates came from the malignant mastocytosis group; eosinophilia, plasmacytosis and fibrosis were seen significantly more often in malignant than in systemic mastocytosis, but blood vessel hyperplasia and germinal centre hyperplasia were encountered with the same high frequency in both groups; and mast cell atypia tended to be more pronounced in malignant mastocytosis; this diagnosis could therefore easily be missed without naphthol AS-D chloroacetate esterase staining.(ABSTRACT TRUNCATED AT 250 WORDS)