Bone Marrow Oxalosis in a Patient With Pancytopenia Following Bilateral Nephrectomy

Dear Editor, Bone marrow (BM) oxalosis is a type of systemic oxalosis wherein oxalate is deposited in BM. It is characterized by cytopenias, leukoerythroblastosis, and hepatosplenomegaly [1] as well as BM findings of calcium oxalate crystals that are birefringent under polarized microscopy and granulomatous structures [2]. Hyperoxaluria (excessive urinary excretion of oxalate) can develop into systemic oxalosis when oxalate is deposited in organs [3]. Hyperoxaluria is classified as primary or secondary. Primary hyperoxaluria is an autosomal recessive disease with defective oxalate metabolism [3] in which the overproduction of oxalate results from an enzyme deficiency in the liver; its clinical presentation involves nephrocalcinosis and renal impairment. Systemic deposition of excess oxalate occurs in the bone and all organs and tissues, except the liver. The retina, arteries, peripheral nervous system, myocardium, thyroid, skin, and BM are the major areas of oxalate deposition. Bone is the most common site, although the bone lesions can mimic clinical renal osteodystrophy [4, 5]. Primary hyperoxaluria includes three types of enzyme deficiency. The most common form is primary hyperoxaluria type I, with an incidence rate of approximately 1/120,000 live births per year in Europe. It is caused by a mutation in the AGXT gene resulting in a functional defect of the liver enzyme alanine-glyoxylate aminotransferase and represents 80% of primary hyperoxaluria. Primary hyperoxaluria type II is caused by a deficiency of glyoxylate reductase/hydroxypyruvate reductase (GRHPR), and type III is caused by a deficiency of the mitochondrial enzyme HOGA1 [2, 3]. Secondary hyperoxaluria occurs when dietary and intestinal absorption of oxalate or intake of oxalate precursors is increased and the intestinal microflora is changed [3]. The clinical presentation of secondary hyperoxaluria is similar to that of primary hyperoxaluria, although systemic oxalosis is less common [3]. We present a case of BM oxalosis with pancytopenia in a patient who had been on hemodialysis after bilateral nephrectomy due to recurrent nephrocalcinosis. A 51-yr-old male patient underwent a BM biopsy due to pancytopenia. He had been on hemodialysis via an arterio-venous graft since 2009 when he underwent a bilateral nephrectomy owing to recurrent renal stones and renal failure. One of his siblings had died owing to end-stage renal disease in his or her 30s (the sex is unknown). The patient had no history of a highoxalate diet or gastrointestinal symptoms. His complete blood count revealed a Hb level of 5.7 g/dL, white blood cell count of 1.2×10/L (absolute neutrophil count 0.81), and platelet count of 98×10/L. Anemia persisted for five years despite treatment with erythropoietin, and leukopenia and thrombocytopenia also developed. Radiography revealed diffuse sclerotic changes and