[Mycobacterium avium tumoral infection mimicking a lung adenocarcinoma: A potential diagnostic pitfall]

The incidence of atypical mycobacterial infection in Europe is estimated at one case per 100,000 persons/year. Despite the low incidence of Mycobacterium avium infection, it can result in a nodular lesion simulating lung cancer. We report a case of atypical mycobacteriosis, mimicking lung cancer, which led to a lobectomy.

It was a right pulmonary upper lobe nodule found in a 63-year-old COPD patient, partially nephrectomized for renal carcinoma, and weekly treated by methotrexate for rheumatoid arthritis. FDG uptake was weakly positive on PET-CT (SUV=2.2) in the upper fissure. Bronchoscopy yielded no lesions and no bacteriological findings. Percutaneous transthoracic lung biopsy revealed lung adenocarcinoma stage T1 (a) N0M0. An upper lobectomy with lymphadenectomy was performed. Histological examination revealed epithelioid granuloma surrounded by giant cells suggestive of tuberculomas. The bronchial washing fluid culture was positive for Mycobacterium avium after 7 weeks.

In pseudo-neoplastic forms of atypical mycobacteriosis, the presence of alveolar, inflammatory cytonuclear abnormalities can mimic an adenocarcinoma. Making the difference between the cytonuclears defects related to inflammation or neoplasia remains a daily challenge in histopathology.