Under Ultraviolet Light: Unmasking Concomitant Trichobacteriosis and Erythrasma in a Dark Phototype Patient

Trichobacteriosis axillaris and erythrasma are superficial infections caused by Corynebacterium species that affect intertriginous areas and may coexist despite being infrequently recognized. We report the case of a 48-year-old man with well-controlled type 2 diabetes who presented with axillary bromhidrosis and pruritus involving the axillary and inguinal folds. Clinical examination revealed yellowish hair shaft concretions in the axillae and brownish scaly patches in the inguinal folds. Dermoscopy demonstrated characteristic sheath-like concretions surrounding the hair shafts and a homogeneous brownish background with fine scaling. Ultraviolet examination showed coral-red fluorescence of the inguinal lesions together with enhanced visualization of yellowish-green luminescent hair shaft concretions, confirming concomitant erythrasma and trichobacteriosis. The patient was successfully treated with hygiene measures and oral erythromycin, resulting in marked clinical improvement. This case highlights the value of combining dermoscopy and ultraviolet imaging as rapid, non-invasive diagnostic tools for concomitant corynebacterial infections, particularly in patients with darker skin phototypes.