Cutaneous tuberculosis as metastatic tuberculous abscess

Cutaneous tuberculosis (CTB) continues to be one of the most difficult diagnoses to make because of the wide variations in its clinical appearance, histopathology, immunology and treatment response.(1,2) The incidence of this disease has increased in the 21st century, due to a high incidence of HIV infection and multidrugresistant pulmonary tuberculosis.(3,4) Although CTB accounts for only 1.5% of all cases of extrapulmonary tuberculosis and 0.15% of all cases of skin disease, given the high prevalence of tuberculosis in many countries, these numbers are significant.(1,2) Mycobacterium tuberculosis, M. bovis, and the BCG vaccine can all cause CTB.(5) In most cases, tuberculosis is transmitted via the airborne route, and skin manifestations are a result of hematogenous spread or direct extension from a focus of infection. However, primary inoculation can occur through direct introduction of the mycobacteria into the skin or mucosa of a susceptible individual by trauma or injury. The risk increases in the presence of HIV infection, intravenous drug abuse, diabetes mellitus, immunosuppressive therapy, malignancy, end-stage renal disease, or infancy.(5,6) Albeit a rare sign, CTB should be considered in the differential diagnosis of skin lesions, especially in individuals with a history of tuberculosis. A 68-year-old male presented with a six-month history of weight loss and asthenia. He was a retired factory worker and former smoker, with a history of pulmonary tuberculosis in his youth (two distinct episodes, 20 years apart, the treatment regimens employed in those episodes being unknown), schizophrenia, osteoarticular pathology, and reflux esophagitis. The patient also presented with two anterior thoracic skin swellings (22 × 60 cm and 80 × 30 cm, respectively) that were painful on palpation, with an elastic consistency and without local warmth on the overlying skin (Figure 1). He reported that the swellings had first appeared one month earlier. He reported no fever or respiratory complaints. No lymph nodes were detected. A CT scan of the chest showed two liquid collections in the anterior chest wall, with a dystrophic aspect, together with thickening of the costal arch and the adjacent costal cartilage. Diagnoses such as staphylococcal abscess, mixed bacterial infection, nocardiosis, atypical mycobacterial infections, and deep fungal infections were considered. A biopsy of one of the swellings showed granulation tissue with lymphocytes, plasma cells, and histiocytes, with suppurative areas and a fistulous tract. In sputum smears, staining for AFB was negative, although a PCR of a sputum sample was positive for M. tuberculosis. Serology for HIV was negative. The patient was referred to a center for the treatment of thoracic diseases, for evaluation and treatment. Another CT scan of the pulmonary parenchyma revealed some fibrotic changes in both lung apices. Sputum smear staining for AFB was again negative, although a culture of the biopsy sample was positive for M. tuberculosis. Drug susceptibility testing showed that the strain was susceptible to isoniazid and rifampin, as well as to all of the first-line antituberculosis drugs tested. The patient was started on four antituberculosis drugs, at doses adjusted for body weight—isoniazid (300 mg/day); rifampin (600 mg/day); pyrazinamide (1,500 mg/day); and ethambutol (1,000 mg/day).