Primary Cutaneous Actinomycosis in an Atypical Location – An Unusual Presentation

Primary cutaneous actinomycosis is an exceedingly rare presentation of a chronic granulomatous infection caused by Actinomyces israelii , typically involving the cervicofacial, thoracic, or abdominal regions. Isolated cutaneous involvement, particularly in atypical locations and without antecedent trauma or systemic disease, poses a diagnostic challenge. We report a 17-year-old immunocompetent female who presented with nodular plaques with overlying crusted lesions and atrophic scarring over the left elbow. Dermoscopy revealed yellow-orange globules with central black dots, arborizing vessels, and white structureless areas. Gram staining demonstrated filamentous Gram-positive bacilli. Histopathology showed microabscesses containing bacterial filaments surrounded by the Splendore–Hoeppli phenomenon, confirming cutaneous actinomycosis. No special stains were needed. The patient was treated with oral amoxicillin (875 mg) and clavulanic acid (125 mg) twice daily, resulting in marked improvement within 10 days. This case underscores the importance of considering primary cutaneous actinomycosis in the differential diagnosis of chronic indurated plaques, particularly when dermoscopy and histopathology suggest granulomatous infection. The case is unique due to its unusual location, absence of trauma, and successful treatment without surgical intervention. Early recognition and antibiotic therapy can lead to excellent outcomes in such rare presentations.