SKIN September 2022 Volume 6 Issue 5 (c) 2022 THE AUTHORS. Published by the National Society for Cutaneous Medicine. 451 SKIMages Erythrasma Under Wood’s Lamp and the “Coral-Red” Glow Danny Zakria, MD, MBA1, Nicholas D. Brownstone, MD2, McKenzie A. Dirr, BA, BS3, Darrell Rigel, MD, MS4 1 National Society for Cutaneous Medicine, New York, NY 2 Department of Dermatology, Temple Health, Philadelphia, PA 3 Medical University of South Carolina, Charleston, SC 4 Department of Dermatology, Mount Sinai Icahn School of Medicine, New York, NY We present a case in which a 54-year-old male with Fitzpatrick skin type II presented to clinic with well-circumscribed dark brown patches with surrounding scale in his bi- lateral inguinal folds. He reported that he first noticed the rash about two weeks prior to presentation and applied OTC anti-fungal creams with no improvement. He stated that he has never had a similar rash before, and he noted that the only associated symptom was occasional pruritus. Examination with Wood’s lamp revealed a bright “coral-red” fluorescence (Figure 1) and helped confirm the diagnosis of erythrasma. Erythrasma is a cutaneous bacterial infection most commonly caused by Corynebacterium minutissimum.1 Corynebacterium minutissimum is a Gram- positive bacillus that constitutes the normal Figure 1. Coral red fluorescence characteristic of erythrasma SKIN September 2022 Volume 6 Issue 5 (c) 2022 THE AUTHORS. Published by the National Society for Cutaneous Medicine. 452 microflora of the skin.2 It has a predilection for moist areas of the body such as the axillae, inframammary folds, interdigit spaces, and the intergluteal cleft.1 C. minutissimum produces a chemical called coproporphyrin type III, which leads to the characteristic “coral-red” glow when examined under Wood’s lamp.2 Importantly, bathing can remove the porphyrin and lead to a false-negative result.2 Erythrasma classically presents as well-demarcated dark-brown macules and later coalesces into larger patches in intertriginous skin.3 The rash can be confused with other common pathology including candidiasis, dermatophytosis, pityriasis versicolor, and inverse psoriasis. Candidiasis is a fungal infection most commonly caused by Candida albicans.1 The rash is typically erythematous and scaly with evidence of satellite lesions. Dermatophyte infections can also present as erythematous and scaly plaques. Both candidiasis and dermatophyte infections can be identified using potassium hydroxide preparation.1 Of note, approximately 30% of patients with interdigital erythrasma may have a coexisting dermatophyte or candida infection. Pityriasis versicolor lesions can be hyperpigmented or hypopigmented but usually do not feature scale or well- demarcated borders as seen in erythrasma. Inverse psoriasis presents as an erythematous, non-scaly plaque in intertriginous lesions. Wood’s lamp offers a quick and non-invasive method of diagnosing erythrasma and distinguishing it from these other similar conditions. There are several treatment options for erythrasma including both topical and systemic therapy. Topical therapy consists of clindamycin, fusidic acid, mupirocin, and Whitfield’s ointment while systemic therapy includes oral clarithromycin, erythromycin, and tetracycline.4 There is no consensus on optimal first-line agent, but topical therapy is generally preferred to limit adverse effects.1 For intertriginous disease, it is important to add a topical agent, often in conjunction with systemic therapy, in order to obtain clearance.4 While there is limited data on duration of treatment, most studies suggest a 2-week course. A thorough HPI, high index of suspicion and appropriate use/interpretation of the Wood’s lamp exam can allow for quicker diagnosis and effective therapy. Conflict of Interest Disclosures: None Funding: None Corresponding Author: Danny Zakria, MD, MBA National Society for Cutaneous Medicine One Harbor Square Suite 325 Ossining, NY 10562 Email: dzakria13@gmail.com References: 1. Forouzan P, Cohen PR. Erythrasma Revisited: Diagnosis, Differential Diagnoses, and Comprehensive Review of Treatment. Cureus. 2020;12(9):e10733. Published 2020 Sep 30. doi:10.7759/cureus.10733 2. Chen D, Ferringer TC. Red-brown patches in the groin. Cutis. 2018;101(6):416-420. 3. Riquelme IL, Moyano EG. Axillary and inguinal erythrasma. CMAJ. 2021;193(39):E1535. doi:10.1503/cmaj.210310 4. Holdiness MR. Management of cutaneous erythrasma. Drugs. 2002;62(8):1131-1141. doi:10.2165/00003495-200262080-00002