A 78-year-old woman had a 30-year history of rheumatoid arthritis, of late treated with prednisolone and methotrexate. A week before admission she had first noticed a mass about 3 cm in diameter, at the lower end of a scar from a Billroth II gastric resection for gastric ulcer, performed 4 months before. She reported to have lost 6.5 kg in weight. On admission a moderately mobile, hard mass was palpated on the abdomen.
Ultrasound and computed tomography revealed a superficial, inhomogenous space-occupying lesion with poorly circumscribed margins.
After two days the skin over the mass became reddened and a laparotomy was performed because an incarcerated herniation was suspected. An abscess and inflammatory adhesions were found in the area of the transverse colon, histologically shown to be a chronic purulent abscess with granular clusters of pathogens indicating actinomycosis. After 3 weeks' treatment with imipenem i.v. the patient became free of symptoms, oral doxycyclin was continued for a further 6 months.
Actinomycosis should be considered in the differential diagnosis of a tumour of undetermined benignity in the region of the head, chest or abdomen in immunosuppressed patients. This bacterial infection should be thought of especially if the gastrointestinal mucosa has been penetrated by invasive procedures.