Cutaneous tuberculosis co-infected with Pseudomonas aeruginosa in a chronic granulomatous ulcer: a diagnostically challenging case report

Abstract Background Cutaneous infectious granulomas are generally considered to be caused by pathogens such as mycobacteria, in particular Mycobacterium tuberculosis or atypical mycobacteria, fungi, or parasites. Pseudomonas aeruginosa ( P. aeruginosa ) is a common colonizer of chronic wounds but is rarely considered a cause of granulomatous inflammation. We report a diagnostically challenging case of cutaneous tuberculosis co-infected with P. aeruginosa in a chronic granulomatous ulcer. Initial empirical therapy produced partial clinical improvement, but the diagnosis was confirmed only after mycobacterial culture. Based on post-discharge culture results, the diagnosis was revised to culture-confirmed cutaneous TB co-infected with P. aeruginosa . Case presentation A 71-year-old man with a three-year history of recurrent right thigh ulcers was admitted with an extensive shallow ulcer (approximately 20 × 15 cm) and surrounding pustules. Histopathology revealed epithelioid cell granulomas, and consecutive wound cultures grew only P. aeruginosa . The patient was treated with intravenous piperacillin-tazobactam and linezolid for 16 days, followed by 15 additional days of oral linezolid after discharge, achieving partial improvement during hospitalization and complete healing within approximately one month. After discharge, mycobacterial culture of the wound tissue turned positive for Mycobacterium tuberculosis . The final diagnosis was cutaneous TB with P. aeruginosa co-infection, and the favorable clinical response may have been partly attributable to the anti-tuberculous activity of linezolid. Over an 18-month telephone follow-up, the patient reported that the ulcer remained completely healed with no recurrent or new skin lesions; however, no objective reassessment was performed, and microbiological cure cannot be confirmed. Conclusions This case demonstrates that in a chronic granulomatous ulcer co-infected with P. aeruginosa , an empirical regimen containing linezolid may produce partial clinical improvement that could delay the correct diagnosis Linezolid is a second-line anti-tuberculous agent, and standard combination anti-tuberculosis therapy remains the treatment of choice once the diagnosis is confirmed. In addition, the anti-tuberculous effect of linezolid may create a diagnostic pitfall, as the clinical improvement may be falsely attributed to the antibacterial coverage of P. aeruginosa alone. A high index of suspicion for TB must be maintained in chronic granulomatous ulcers, particularly when the therapeutic regimen includes agents with anti-tuberculous activity.