A swollen knee in a patient with refractory anaemia

CASE REPORT A 63-year old man with refractory anaemia with excess of blasts and a history of heart failure, diabetes and hyperuricaemia, presented with pain, warmth and swelling in the left knee. Blood sample showed white cell blood count 3,840/μL (normal formula), haemoglobin 7.1 g/dL, platelets 117,000/L, eritrosedimentation rate 66 mm/h, normal serum creatinine and uric acid. He had no history of neutropenia, fever or recurrent infections. X-ray of the knee did not show any erosion or lytic lesion. Arthrocentesis produced turbid fluid, with elevated cell count (81,000/μL, mainly polimorphonuclear cells), no urate crystals, normal chemical pattern, sterile culture. Synovial fluid smear showed a huge neutrophilic cellularity with scattered mononuclear cells looking like medullar myeloid blasts. The microscopic examination identified a myeloid infiltration as the cause of arthritis.
DISCUSSION AND CONCLUSIONS Rheumatic phenomena in myelodysplastic syndromes have a prevalence of 10% and include vasculitis, neuropaties, glomerulonephritis, lupus-like syndrome, inflammatory bowel disease, lung infiltrates and arthritis. The pathogenesis is usually autoimmune, as in all paraneoplastic syndromes. In our case, arthritis was due to a direct invasion of blasts. This phenomenon is rarely observed in acute leukemias and was not described yet in myelodysplastic syndromes. Synovial fluid analysis is critical to define the ethiology of an articular effusion, microscopical examination is strongly recommended but it is not always carried out. This case shows how simple diagnostic tests can easily disclose rare conditions.