A case of a 4-year-old boy with difficult-to-diagnose skin infection with nontuberculous mycobacteria

Nontuberculous mycobacteria infections have become increasingly common in recent years and have even been confirmed in children. In addition to other organs, they can even affect the skin; nevertheless, in children lymphadenitis is the most common manifestation of the infection. The diagnosis of mycobacterial skin infection is based on patient history, clinical picture, histopathological changes, and tuberculin test result. Evidence of the causative agent in the lesion is confirmed with cultivation and PCR, two of the main tests that help determine the type of the causative mycobacteria. Here we report the case of a 4-year-old boy that presented with a few pink-to-livid papules and one plaque with a central crust on the skin of the left knee and an enlarged popliteal lymph node, highly suspicious of nontuberculous mycobacteria infection. Among the laboratory results, only a positive QuantiFERON and Mantoux test stood out. In addition, in the histopathological report, superficial and deep inflammatory elements were described, which could be due to an infection with nontuberculous mycobacteria. Despite negative cultivation and PCR, in agreement with a pediatric pulmonologist we decided to introduce antibiotic therapy for 6 months. Treatment was successful, we achieved regression of the skin lesions, and lymphadenitis was no longer present.