A 46 year old male with a progressively enlarging chest mass, weight loss and cough was admitted to hospital for further investigation and management of presumed metastatic lung cancer. The patient had epilepsy treated with phenytoin. Habits included smoking and heavy alcohol use. Phenytoin-related gum hypertrophy and poor dentition were present. There was a 5cm left-sided chest wall mass with central ulceration. A 3 cm mass was palpable in the right gluteal region. Laboratory investigations revealed a sodium of 129 (137-145) mmol/L, C-reactive protein of 160 (<8) mg/L and haemoglobin 99 (135-175) g/L. Chest computed tomogram revealed a 13 cm lung mass extending from right upper to lower lobe and extensive lymphadenopathy. Biopsy of the chest wall mass was negative for malignancy but demonstrated an inflammatory infiltrate with collections of filamentous bacteria and associated Splendore-Hoeppli reaction. Cultures from the chest mass and a gluteal aspirate grew Aggregatibacter actinomyceteconcomitans at day two. Eikenella corrodens and Fusobacterium nucleatum grew at day four. At day seven, Gram-positive branching bacilli were noted on anaerobic plates and identified as Actinomyces israelli.

Following surgical debridement of the chest wall lesion, the patient was treated with benzylpenicillin for six weeks followed by oral amoxycillin with good response.

Actinomycosis is a rare disease which may mimic other conditions, in particular malignancy. Actinomycetes are generally commensals but may become pathogenic when mucosa is breached. In infection, Actinomycetes is frequently found in association with particular “companion” bacteria. Characteristic features of infection include extension of infection across tissue planes, the presence of “sulphur granules” in exudates and the development of sinus tracts. Cervicofacial actinomycosis is most common, followed by thoracic and pelvic disease. Risk factors include poor dentition, aspiration, alcohol use and long-term indwelling intra-uterine devices. Prolonged courses of antibiotics are required, with the treatment of choice being benzylpenicillin.