Chronic myelomonocytic leukaemia: a presentation with rare extramedullary involvement

A 74 ‐year ‐old male with a recent diagnosis of chronic myelomonocytic leukaemia (CMML) was admitted for rapidly progressive renal failure (RPRF), associated with gait impairment due to muscle weakness and pain in the lower limbs. After exclusion of pre ‐renal and post ‐renal causes of RPRF, the workup revealed monocytosis, high levels of inflammatory markers, hypergammaglobulinaemia, nephrotic proteinuria and high serum and urinary lysozyme levels. Renal biopsy confirmed the diagnosis of lysozyme ‐induced kidney injury and CMML ‐associated vasculitis. An electromyogram also revealed sensorimotor axonal polyneuropathy. The patient was started on pred‐ nisolone and azacitidine. Improvement of limb symptoms and a decrease in monocyte count, renal function values, inflammatory markers and proteinuria were subsequently seen. Although lysozyme levels are consistently elevated in CMML, lysozyme ‐induced kidney injury is a rare cause of renal failure. Filtered lysozyme appears to act as a direct tubular toxin and lysozymuria has been proposed as a valuable tool for detection of tubular damage. Polyneuropathy secondary to CMML is also infrequent and may be due to autoimmune mechanisms. We describe a case of lysozyme‐ ‐induced kidney injury, vasculitis and axonal polyneuropathy, presumably secondary to CMML, in which prednisolone and azacitidine seem to have been helpful in treating extramedullary leukaemic involvement.