The nature of crystals in plasma cells present in a case of apparently benign biclonal gammapathy

: A 77 years old white man presents, in his blood serum, a moderate gammapathy with 2 monoclonal peaks, IgAk and IgGlambda, and in his urine a little quantity of BJk, without any clinical or radiological manifestation. The sternal bone marrow showed 3-5% plasmacells, mostly containing many needlelike inclusions in the cytoplasm. These inclusions, red-violet at the May-Grunwald-Giemsa, were PAS and Sudan negative; positive at the Danielli reaction (for proteins). The alpha-naphtil-acetate-esterase and the acid phosphatase were present in one outer layer of the inclusions; ATP-ase was absent. At the electron microscopy, the inclusions were localized outside the rough endoplasmic reticulum; they exhibited a crystalline structure and were surrounded by an envelope which reminded the lysosomes. Basing on the morphological pattern, as well as on the presence of some lysosomal enzymes and on the lack of staining of crystals with fluorescinated anti-Ig sera, the hypothesis is stressed of an abnormal lysosomal hyperactivity, possibly leading to crystallization of the enzymatic proteins in the lysosomes.