Isolated Subcutaneous Abscess: A Rare Presentation of Extrapulmonary Tuberculosis

To The Editors: Soft tissue tuberculosis (TB) is one of the rare manifestations of extrapulmonary tuberculosis (EPTB). We presented a 2-year-old patient with isolated soft tissue TB, rarely reported in the literature. A 2-year-old girl has been admitted to our hospital with persistent painless swelling in her leg for 9 months. There was no history of fever, night sweats, weight loss or trauma. Her medical history was unremarkable, and she had no contact with a TB patient. She was vaccinated with the Bacille Calmette Guérin (BCG) at 2 months. The physical examination revealed a mass without erythema or pain in the posteromedial left calf. Pulmonary, cardiac and abdominal examinations were unremarkable. Lymphadenopathy was not detected. The tuberculin skin test was negative. Magnetic resonance imaging showed a 76 × 31 × 42 mm cystic mass in the medial left calf proximal-posterior with a thick capsule, mildly elevated proteinaceous content, edema and inflammation in the surrounding muscle and soft tissue planes, and a peripheral rim-like capsular contrast interaction (Fig. 1). Bone structures were observed in normal morphology.FIGURE 1.: Coronal Dynamic 3D image of a 76 × 31 × 42 mm diameter cystic mass with a thick capsule with peripheral rim-like capsular contrast interaction in postcontrast images in the proximal-posterior middle part of the left cruris.The abscess was drained under general anesthesia. Gram staining, Kinyoun staining for acid-fast bacillus, and bacterial culture of the abscess did not reveal any causing agents. But Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) Ultra identified the rifampicin-susceptible Mycobacterium tuberculosis complex. No growth was detected in the mycobacterial culture. Histopathology revealed necrotizing granulomatous inflammation. Other than soft tissue, no pulmonary or extrapulmonary involvement was identified. The case was assessed for congenital and acquired immunodeficiencies. The human immunodeficiency virus antibody was negative. Immunoglobin values and lymphocyte panels were found to be normal. Whole-exome sequences did not reveal any rare potential loss of function or missense variation in genes previously associated with susceptibility to mycobacterial diseases in otherwise healthy individuals, such as IFNGR1, IFNGR2, STAT1, JAK1, IRF8, SPPL2A, IL12B, IL12RB1, IL12RB2, IL23R, ISG15, TYK2, RORC, CYBB, NEMO and ZNFX1.1,2 The homozygosity of a common TYK2 allele, p.P1104A, related to severe mycobacterial diseases was not detected in our patient.3 A 3-drug anti-TB treatment was started (2 HRZ followed by 4 HR). No recurrence was observed in the 2-year follow-up. Subcutaneous abscesses with osteomyelitis have been reported as a complication of BCG vaccination.4 However, as in our case, subcutaneous abscess without muscle or bone involvement has been rarely reported in children.5,6 Diagnosing EPTB is difficult because clinical samples taken from relatively inaccessible areas may be paucibacillary, reducing the sensitivity of diagnostic tests. The tuberculin skin test may be nonreactive in 40% of cases.7 According to the meta-analysis, interferon-gamma release assays (IGRAs) have low sensitivity and specificity for EPTB diagnosis, especially in low/middle-income countries with significant TB burdens.8 IGRA was not performed in our patient due to low sensitivity and specificity in younger children. The patient was diagnosed according to Xpert MTB/RIF Ultra and histopathological examination results. World Health Organization has approved using the Xpert MTB/RIF Ultra as an initial diagnostic test for sputum, nasopharyngeal aspirate, gastric aspirate or stool for diagnosing pulmonary TB in children younger than 10 years.9 However, experts state that the diagnostic efficiency of Xpert MTB/RIF Ultra on EPTB samples needs to be optimized.10 The case presented here emphasized that TB may have unusual clinical presentations and should always be considered in endemic areas. Moreover, it should be kept in mind that microbiological examination plays an essential role in the evaluation of mass as well as histopathologic examination.