Unusual intracellular and extracellular crystal inclusions in light chain multiple myeloma.

Correspondence: Salvatore Casciaro, M.D., II Divisione di Medicina, Ospedale S. Martino, largo Rosanna Benzi, 16132 Genoa, Italy. Phone: international +39-010-5552392 – Fax: international +39-0105556661. Herein we report the light microscopy observation of intracellular and interstitial crystalloid deposits found in the bone marrow of two patients with light chain multiple myeloma (MM). The first patient was a 65-year old female referred to a nephrology unit because of acute renal failure, severe anemia (Hb 6.3 g/dL), and thrombocytopenia (Plt 92 109/L). Electrophoresis showed a marked reduction of total proteins, hypogammaglobulinemia and a monoclonal component ( light chain) in both serum and urine samples. Severe diffuse osteoporosis and multiple vertebral collapses were present. The second patient was a 74-year old female with IgG MM, already treated with melphalan-prednisone. She came to our observation because of severe anemia, thrombocytopenia, multiple osteolytic lesions and a nephrotic syndrome with excretion of chains. The two patients were partially responsive to chemotherapy (VAD and CTX-DEX) and survived 4 and 5 months. In both patients bone marrow specimens revealed extensive (80%) infiltration by immature and atypical plasma cells. The histologic pattern was characterized by the presence of May-Grünwald-Giemsa negative rods and needle-shaped inclusions (Figure 1), both in the plasma cell cytoplasm and in the intercellular spaces (Figure 2). Aggregates of these rods were also detected in the cytoplasm of macrophages (Figure 3). Additional investigations of these inclusions (i.e. electron microscopy and immunohistochemical characterization) could not be performed. In the first patient, periumbilical fat tissue was positive by Congo red staining, whereas marrow inclusions were negative. In the same patient, marrow aspiration after therapy showed a marked reduction of both plasma cells and inclusions (Figure 3). It is feasible, however, that the crystal inclusions may consist of monoclonal proteins formed and released by malignant plasma cells and subsequently phagocytosed by macrophages. Although in MM patients cytoplasmic and nuclear crystal inclusions have been already reported,1-3 our observation is of interest as it demonstrates the presFigure 1. Bone marrow smear stained by May-GrünwaldGiemsa (MGG) showing diffuse crystalloid deposits in light chain MM ( 40).