Cutaneous actinomycosis presenting as chronic mastitis

Actinomycosis is a chronic granulomatous suppurative infection caused by anaerobic actinomyces. Primary cutaneous involvement is uncommon because of the exclusively endogenous habitat of the organism. We describe a very unusual presentation mimicking chronic mastitis. A 35‐year‐old woman presented 7 months post‐partum with tenderness and induration in the right breast. She was pyrexial and felt systemically unwell. An initial diagnosis of mastitis was made. Treatment with penicillin, imipenem, co‐amoxiclav and metronidazole had no effect. Skin biopsy revealed the characteristic ‘sulphur granules’ of actinomycoses in the deep dermis. Long term oral clindamycin (> 12 months) has produced a very good response clinically, with a concomitant decrease in inflammatory markers. Cutaneous actinomycosis has been described by haematogenous spread from visceral organs or after trauma. The organism is difficult to culture and is often diagnosed histologically by the presence of ‘sulphur granules’. It is very sensitive to penicillin but prolonged treatment is needed.