Unusual and memorable. A tender swelling of the dorsum of a hand in a middle aged woman.

A healthy 42 year old woman presented with a tender red-bluish fluctuating swelling of the dorsum of her left hand, which had been present for five weeks. The swelling was not warm and originated from one or two extensor tendon sheaths (fig 1). There had not been any previous trauma. Treatment with trimethoprim/sulfamethoxazole by the general practitioner was not successful. Until one year earlier she had worked with fish tanks containing tropical fishes. She had stopped this work because of an ulcer on the distal phalanx of the third left finger, which disappeared without treatment. Laboratory examinations were normal as were x ray examinations of the hands. A punctate from the swelling yielded necrotic material that was negative with a Gram stain and did not show growth on routine culture media. Acid-fast rods, however, were seen in the auramine stain. After three weeks a culture grew Mycobacterium marinum. After treatment with rifampicin 600 mg a day and ethambutol 1000 mg a day for five months the patient recovered completely (fig 2). When local swelling of the hands occurs one has to consider an infection with M marinum whenever there is a history of manual contact with fish tanks or swimming pools.