A unique malignant T‐cell lymphoproliferative disorder with neutropenia simulating hairy cell leukemia

The association of neutropenia with an indolent chronic T‐suppressor cell lymphoproliferative disorder (LPD) has been well documented. The morphologic features and course suggest that this is a benign disorder. The authors studied a 58‐year‐old man with a chronic T‐cell LPD, splenomegaly, and neutropenia. Chromosomal analysis revealed multiple abnormalities which progressively increased in number as the marrow lymphocytosis became more prominent. Subsequently he developed small bowel infiltration. A splenectomy resulted in only brief improvement in the neutropenia. Immunopathologic examination of the spleen was consistent with a well‐differentiated lymphocytic lymphoma of a mature peripheral T‐cell type without subset specific markers. Granulocyte–monocyte colony (CFU‐GM) formation from the patient's marrow was normal and not augmented by T‐cell depletion. Neither the patient's splenic T‐cells nor serum suppressed granulopoiesis. In contrast to previous T‐LPD with neutropenia whose malignant nature has been questioned, the clinical, cytogenetic, and pathologic features and course in this case indicate a malignant lymphoid process which was effectively treated with chemotherapy. Although the histologic pattern of red pulp involvement simulated hairy cell leukemia, that diagnosis was excluded by this patient's clinical, morphologic, and cytochemical features.