A 26-year-old man who had a kidney transplant in 2009 as a result of nephropathic cystinosis was examined for bicytopenia (platelet count, 98 × 109/L; hemoglobin, 113 g/L). May-Grünwald-Giemsa staining showed a normocellular bone marrow with numerous megakaryocytes without dysplastic features. Macrophages were profuse, and they contained abundant light gray hexagonal crystals of different sizes (panel B). These crystals appeared birefringent under polarized light (panel A), consistent with the diagnosis of cystinosis.
Cystinosis is a rare autosomal lysosomal storage disorder caused by a defect in cystine transport. This poorly soluble amino acid accumulates in the lysosomes of various organs, especially kidneys, inducing progressive kidney failure. Patients often suffer cytopenia associated with cystine crystals in the bone marrow, decreased renal production of erythropoietin, hypersplenism (splenomegaly and portal hypertension due to nodular hyperplasia), and myelofibrosis. In the case described here, anemia and thrombocytopenia remained moderate. There was no evidence of bone marrow fibrosis or palpable spleen.
