Ulcerated Lesions on the Right Leg

THE DIAGNOSIS: Mycobacteria infection

Despite the initial biopsy for tissue culture showing no growth, a subsequent biopsy performed 1 month later yielded a positive result. Mycobacterium marinum was identified through organism genome sequencing. The patient was further treated by infectious disease with clarithromycin and ethambutol, with complete resolution of the lesions.

Although initial staining with acid-fast bacilli and tissue culture were negative, we suspected a diagnosis of mycobacterial infection with sporotrichoid spread of multiple nodular and ulcerated lesions that was unresponsive to antibiotics. Performing a tissue culture is crucial for diagnosing mycobacterial skin and soft-tissue infections, as an acid-fast bacilli stain alone cannot distinguish between different mycobacterial species. Lowenstein-Jensen agar is a selective medium specifically used for the culture and isolation of Mycobacterium species. The strict temperature requirement of 30 °C to 32 °C (86-89.6 °F) for the growth of this organism suggests that the infection predominantly affects the limbs, which tend to have a slightly lower temperature compared to the core of the body.¹ In our case, the histologic findings and clinical history suggested granulomatous involvement due to fungi or mycobacteria.

Cutaneous leishmaniasis is characterized by ulcers with possible accompanying nodular lymphangitis; however, the patient did not have relevant travel history. Leishmaniasis results from a parasite transmitted by a sandfly, with most cases occurring in Afghanistan, Algeria, Brazil, Iran, Pakistan, Peru, Saudi Arabia, and Syria.²

Ecthyma gangrenosum is characterized by tender necrotic plaques seen predominantly in immunocompromised patients and is associated with Pseudomonas aeruginosa bacteremia.³ Our patient had lesions present for a duration of 5 months, which is inconsistent with the more rapidly progressing course of ecthyma gangrenosum.

Leukocytoclastic vasculitis may manifest with palpable purpura of the lower extremities. An infectious trigger, such as Mycobacterium, may lead to a leukocytoclastic vasculitis. The histopathologic findings classically demonstrate neutrophil deposition in vessel walls, deposition of fibrin in the vessel lumen, and nuclear debris.⁴

Despite the presence of granulomatous changes in our patient, the presentation of ulcerated nodules in a sporotrichoid pattern on one extremity suggests a diagnosis of infectious etiology rather than sarcoidosis.