LAUSR

In 1977, Esterly et al. coined the term ‘eruptive vellus hair cysts’ (EVHC) to describe an idiopathic, persistent, hyperpigmented, monomorphous, papular eruption observed in two children. On pathology, cysts in the mid-dermis were noted to contain multiple fragmented vellus hair shafts. There have since been nearly 130 cases of EVHC reported in the literature [1]. EVHC typically presents as a 1–7mm symmetrical, monomorphous, skin-colored, and dome-shaped eruption of papules that can be grouped or diffuse. The eruption can present anywhere on the body but has a predilection for the anterior chest, abdomen, upper limbs, and face and may be congenital or acquired [2–4]. Most cases are idiopathic, persistent, and asymptomatic [4]. While the exact mechanism underlying EVHC pathogenesis is unknown, it is thought that a developmental issue in vellus hair follicles causes infundibular occlusion, leading to cystic dilation, hair retention, and hair bulb atrophy [1]. Histologically, the cysts are lined by a stratified squamous epithelium in the top or middle dermis, may contain keratin, and are characterized by the presence of obliquely cut vellus hair shafts. Patients with EVHC tend to seek treatment for cosmetic concerns, and most therapies rely on trials of retinoic acid, surgical removal, or laser with varying results [4]. Here, with consent obtained from the patient, we report a case of a patient who developed EVHC during radiation therapy (RT) for breast cancer. Based on a comprehensive literature review, only eight cases of EVHC have presented after a potential trigger, with the rest considered idiopathic or familial. To our knowledge, this is the first case of EVHC arising after any type of cancer treatment, making it an important cutaneous side effect for dermatologists and oncologists to consider when encountering a similar cutaneous eruption during RT.