Tumour-like ear lesion due to Mycobacterium tuberculosis diagnosed by polymerase chain reaction-reverse hybridization

Sir, At present, detection of mycobacteria in tuberculous skin lesions is difficult. It relies essentially on microscopic examination for acid‐fast bacilli and on culture, both of which are nearly always negative because of the paucity of mycobacteria at the site of infection. If present, culture positivity appears after weeks of incubation due to the slow growth rate of Mycobacterium tuberculosis. In this context, molecular methods, especially if polymerase chain reaction (PCR)‐based, are frequently very useful for confirming the presumed mycobacterial aetiology of a cutaneous lesion. They have high reliability, sensitivity and specificity, and are able to give rapid detection of mycobacterial DNA directly in clinical samples.1, 2 We describe the successful use of one of these molecular methods, the PCR–reverse cross‐blot hybridization assay, for the rapid identification of M. tuberculosis in a case of cutaneous tuberculosis with an uncommon clinical presentation. A 65‐year‐old woman was seen for a multilobulated tumour‐like lesion causing an abnormal enlargement of the helix and lobe of the left ear. The lesion had a smooth surface and was painless, red‐brownish in colour, and firm (Fig. 1A). No regional lymphadenopathy was found. The patient reported that 5 years previously a small erythematous papule had occurred on her ear lobe, slowly spreading to involve the entire ear. She denied travelling abroad. Blood tests were normal, as were chest X‐ray and computed tomography of the chest and abdomen. The purified protein derivative test was strongly positive at 48 h (about 7 mm in diameter). Cultures of sputum and urine were negative for M. tuberculosis. Histology of the lesional skin showed many confluent granulomas with epithelioid cells, many giant Langhans cells, and small centres of caseous necrosis (Fig. 1B). This pattern was indicative of cutaneous tuberculosis, although periodic acid–Schiff and Ziehl–Neelsen staining was negative.