Pathology of the lymph node and spleen in systemic mast cell disease.

The spleen and lymph node are two of the most common organs involved in systemic mast cell disease (SMCD). However, SMCD infiltrates in the spleen and lymph node have a broad spectrum of morphological patterns which can make it difficult to recognize the diagnosis, especially when specimens are examined from patients in whom SMCD is not suspected. We reviewed the pathological features of 16 spleen and 23 lymph node specimens from 19 patients which represented all available material from a series of 58 Mayo Clinic patients with SMCD. The purpose of this study was to investigate the pathological manifestations of SMCD involvement in the spleen and lymph node and to address difficulties in differential diagnosis. All compartments of the spleen and lymph node were found to be affected by SMCD. SMCD lesions in the spleen were found in a paratrabecular (92%), parafollicular (69%), follicular (15%), and a diffuse red pulp (8%) distribution. In the lymph node, mast cell infiltrates affected the paracortex (88%), the parafollicular region (50%), the follicles (25%), the medullary cords (13%), and the sinuses (6%). Mast cells were frequently found in a perivascular location, and associated eosinophilia was common. Because of the broad spectrum of histological manifestations of SMCD in the spleen and lymph node, a wide range of differential diagnoses is discussed including follicular lymphoma, T-cell lymphoma, monocytoid B-cell hyperplasia and lymphoma, Kaposi's sarcoma, and Langerhans' cell granulomatosis.