A Diagnostic Enigma of Cutaneous Atypical Mycobacterial Infection Masquerading as Cutaneous Leishmaniasis

Dear Editor, A 54-year-old male without co-morbidities presented with a solitary painful nodule on the outer aspect of his right foot. Over the next 5–7 days, the lesion evolved into multiple nodules that burst spontaneously, releasing purulent discharge and alleviating pain. Similar lesions subsequently developed on his left foot and left thigh following a similar clinical course. Dermatological examination revealed multiple erythematous nodules with central crusting arranged in a sporotrichoid pattern on a diffusely oedematous background over the lateral right ankle [Figure 1a], a solitary lesion over the dorsum of the left ankle and the right medial malleolus [Figure 2a], and medial aspect of the distal left thigh [Figure 3a]. Notably, the lesion on the lateral left thigh exhibited a volcano-like appearance with central ulceration, raised edges, and a surrounding scaly hyperpigmented rim [Figure 4a]. Dermoscopy revealed a white starburst-like pattern with a peripheral white halo encircling a central ulcer on an erythematous background, with a few regularly distributed hairpin vessels [Figure 5].Figure 1: Multiple erythematous nodules with central crusting in a sporotrichoid pattern on a diffuse oedematous background over the lateral aspect of the right ankle region, before (a), 1 month after treatment (b)Figure 2: Solitary erythematous nodule over the right medial malleolus region before (a), 1 month after treatment (b)Figure 3: Similar lesion over left thigh before (a), 1 month after treatment (b)Figure 4: Volcano-like crater of an erythematous nodule with central ulceration, raised edges, and a peripheral scaly hyperpigmented rim over lateral aspect of left thigh, before (a), 1 month after treatment (b)Figure 5: Dermoscopy (Dermlite-5, x10, polarized) reveals starburst-like pattern with white halo surrounding a central ulcer on a background of erythema with few regularly distributed hairpin vesselsRoutine blood investigations, radiographs of both feet, contrast-enhanced magnetic resonance imaging, a chest radiograph, and contrast-enhanced computed tomography of the chest were all within normal limits. The Mantoux test measured 10 × 10 mm. Ziehl-Neelsen staining of the purulent discharge revealed slender, long, and beaded acid-fast bacilli (AFB) [Figure 6]. A 10% potassium hydroxide smear was negative for fungal elements, and Giemsa staining failed to demonstrate amastigotes of leishmaniasis. Fine needle aspiration cytology from the right foot lesion showed granulomatous inflammation, while a skin biopsy revealed features of cutaneous small vessel leukocytoclastic vasculitis with septal panniculitis and focal giant cells. Gene Xpert for Mycobacterium tuberculosis was negative, and immunohistochemistry for CD1a, for leishmaniasis, was negative.[1] However, the exact non-tuberculous mycobacterial organism could not be isolated as culture on Lowenstein-Jensen medium yielded no growth [Figure 7]. These investigations possibly ruled out cutaneous tuberculosis and cutaneous leishmaniasis.Figure 6: Ziehl-Neelsen stain showing acid fast bacilli (AFB), which were slender, long, and beaded in appearanceFigure 7: Lowenstein Jensen medium showed no growthBased on the diagnostic workup, the patient was diagnosed with cutaneous non-tuberculous mycobacterial infection. In accordance with national guidelines,[2] he was initiated on a multidrug regimen consisting of Rifampicin, Clarithromycin, and Ethambutol, but Amikacin was omitted due to deranged creatinine. Over the ensuing weeks, he exhibited marked clinical improvement with gradual resolution of the nodules and healing of the ulcerated lesions [Figures 1b, 2b, 3b and 4b]. The novelty of this case lies in its presentation mimicking cutaneous leishmaniasis—a common tropical infection characterized by volcano-like ulcers.[3] Non-tuberculous mycobacterial infections of the skin and soft tissues may present in various forms, including Buruli ulcers due to Mycobacterium ulcerans, fish-tank granuloma from Mycobacterium marinum, and localized infections by rapid growers such as Mycobacterium abscessus, Mycobacterium fortuitum, and Mycobacterium chelonae.[4,5] This case underscores the importance of maintaining a high index of suspicion for atypical mycobacterial infections in patients with unusual cutaneous presentations and highlights that repeated, tests may provide crucial diagnostic clues. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.