Eruptive Vellus Hair Cysts in an Unusual Location with Atypical Pathological Features

In 2018, a case was reported of a 20-year-old Asian male with eruptive vellus hair cysts (EVHCs) presenting in an unusual location on the extensor surfaces of his elbows, which posed a diagnostic challenge due to atypical clinical and pathological features. The patient had a history of psoriasis and presented with multiple asymptomatic papules that did not respond to various treatments, including topical steroids, azelaic acid, and oral doxycycline. Attempts to diagnose the condition using a simple extraction technique were unsuccessful. A biopsy revealed granulomatous inflammation near a hair follicle, but no conclusive diagnosis was provided until a careful review of the pathology slides revealed scattered vellus hairs in the dermis, leading to the diagnosis of EVHCs with an endogenous foreign body reaction. This reaction was likely due to a traumatic rupture of the cyst wall, which made the extraction technique unreliable for diagnosis or treatment. The case highlights the importance of recognizing the clinical and pathological spectrum of EVHCs for timely and accurate diagnosis.