The case is reported of a 63 year old man presenting with a rapidly destructive symmetrical polyarthritis and widespread papular nodular skin lesions, confirmed by a biopsy to be due to multicentric reticulohistiocytosis. Biventricular cardiac failure developed secondary to extensive myocardial infiltration with multicentric reticulohistiocytosis, a complication of this disease which has not previously been reported. The joint, skin, and cardiac manifestations of multicentric reticulohistiocytosis substantially regressed following resection of an associated squamous cell carcinoma. This report adds to the small amount of published work which suggests that multicentric reticulohistiocytosis can be a paraneoplastic disease that may respond to treatment directed at the underlying tumour.Multicentric reticulohistiocytosis is an uncommon disease of unknown aetiology sufficiently similar in its presentation to rheumatoid arthritis for it often to be initially mistaken as such. Although the joints and skin are the most commonly affected sites, multicentric reticulohistiocytosis may become a systemic disease with a poor prognosis. ' 2 contained periodic acid-Schiff positive material typical of this disease. The synovial fluid aspirate contained polymorphs, a few macrophages and lymphocytes, but there were no specific features of multicentric reticulohistiocytosis.The patient was initially treated symptomatically with rest, non-steroidal anti-inflammatory drugs (NSAIDs) and intra-articular steroids. The synovitis persisted, however, and cyclophosphamide (15 mg/kg/month) was given by intermittent intravenous infusion. There was some improvement in joint symptoms and synovitis after two infusions but the skin lesions remained static.Three months later the patient presented with dyspnoea at rest and signs of acute biventricular cardiac failure. Flexor tenosynovitis with deformities of the fingers had developed. The skin disease had progressed with the development of several larger nodules which were freely mobile within the subcutaneous tissue over the extensor aspect of his forearms and hands (fig 1) Case report A 63 year old previously healthy man presented with a three month history of polyarthralgia and morning stiffness affecting the hands, wrists, and knees together with an extensive painless, pruritic rash. Examination showed synovitis, bilateral knee effusions, and olecranon bursitis. Crops of red and brown papules 1-5 mm in diameter were present over the chest and abdomen. Xanthelasmata were noted but there were no other cutaneous features of hyperlipidaemia and the examination was otherwise normal.The erythrocyte sedimentation rate was increased at 43 mm in the first hour but the full blood count, plasma urea and electrolytes, liver function tests, fasting lipids, immunoglobulins, and rheumatoid factor were all normal. Hand radiographs showed soft tissue swelling, periarticular osteoporosis, and loss of articular cartilage of the proximal and distal interphalangeal joints. The diagnosis of multicentric ret...