To the Editor: Semenzato et al. proposed new criteria for large granular lymphocyte (LGL) leukemia because patients with low levels of GL were similar to those with levels greater than 2,000 GL/l [1]. LGL leukemia is a GL proliferative disease often accompanied by pure red cell aplasia (PRCA). T-cell LGL leukemia is a clonal disease, and the phenotype of leukemic cells is CD3 + 4 -8 + .
PRCA with thymoma is often associated with peripheral T cell expansion. We previously reported a case of PRCA with thymoma in which the T-cell receptor β€ of both the thymus and peripheral mononuclear cells was rearranged [2]. Thymoma and PRCA may be caused by T-cell clonal expansion, leukemia. We examined four patients with PRCA and thymoma (Table I), one of which was previously reported. Three of the four showed CD3 + 4 -8 + lymphocytosis and two exhibited T-cell receptor β€ rearrangement of peripheral mononuclear cells. Patient 2 showed low levels of lymphocytes and the mononuclear cell's CD4/8 ratio of patient 3 was greater than 1. Due to the low levels of abnormal cells and low sensitivity of Southern blot analysis, we could not confirm the clonality of these two cases. According to treatment of PRCA with thymoma, the response rate of thymectomy was 12% [3]. This limited effectiveness of thymectomy indicated that thymoma did not play a causative role in PRCA.
Loughran reported 129 patients with LGL leukemia [4] and Oshimi et al. examined 33 patients [5]. Neither study noted a complication of thymoma. PRCA with thymoma had been considered a distinct clinical entity from LGL leukemia. The old diagnostic criteria for LGL leukemia was "greater than 2,000 GL/l." The normal value of GL is 223 Β± 99 l [4]. Three of the 4 patients with PRCA and thymoma demonstrated levels greater than the mean + 3 SD (Table I). However, it is unknown whether or not a distinction between 'PRCA with thymoma' and 'PRCA with LGL leukemia' exists. Patients with LGL leukemia showed an indolent clinical course, and immunosuppressive therapy with cyclosporin A or low-dose cyclophosphamide was effective for the clinical symptoms. In contrast, patients with PRCA with thymoma were treated with more aggressive therapy such as surgical resection, intensive chemotherapy, or radiation. As the effectiveness of surgical resection for PRCA with thymoma is limited, PRCA with thymoma should be initially treated with immunosuppressive therapy.