Molluscum contagiosum complicated with epidermal cyst:a case reoportRuixian Niu , Wenjin Geng , YunZou , Weian Kuang , Jiangtao Zheng,Xunguo Yin ,Na Qiao,Department of Dermatology,Corresponding author: Dr. Na Qiao and XunguoYin, Department of Dermatology, The first hospital ofQuJing,Kunming Medical University, Yunnan, China. 29250820@qq.com and yxgkm2008@163.comKey Clinical Message: Molluscum contagiosum (MC) o ften occur in clusters, and the clinical manifestations of the skin lesions are diverse. For isolated or large lesions, they are prone to be confused with other skin diseases clinically. Differential diagnosis is necessary. Early detection and accurate diagnosis are crucial for improving the prognosis of patients.Abstract: MC is a viral infection that affects primarily pediatric patients, sexually active young adults, and immunocompromised people of all ages. Clinically, MC presents as firm rounded papules, pink or skin-colored, with a shiny and umbilicated surface. The histological characteristics microscopic findings are represented by a crateriform invagination of hyperplastic epithelium composed of enlarged keratinocytes containing inclusion bodies known as Henderson–Patterson bodies . In some cases, the morphology of MC lesions can vary, including in immunocompetent children. For example, giant MC can mimic cysts, abscesses, or condyloma. Erosive MC lesions can mimic eczema vaccinatum. Papules might also be pearly white or reddish in color[1]. Here, we report a case report of Molluscum contagiosum complicated with epidermal cyst.Key words: Molluscum contagiosum; epidermal cystCase History/examination: An otherwise healthy 24-year-old Chinese Han man presented with an nodular on the scrotum that had persisted for 1 month. The patient had large skin color nodules in the scrotum without obvious inducment and no obvious self-conscious symptoms before 1 month, and was treated in our outpatient department with topical fusidic acid considering ”epidermal cyst”. After treatment, no improvement was found. In order to seek further diagnosis and treatment, the patient was revisited in our department on June 30, 2024.Physical examination revealed the scrotum showed a hemisbulous swelling about the size of soybean, with moderate movement, medium texture, and no obvious tenderness. The rest of the scrotum showed no obvious similar lesions. [Figure 1a]. Skin biopsy revealed:The epidermis is generally normal, with cystic keratins visible in the dermis and eosinophilic inclusions visible around the sac wall. [Figure 2a、Figure 2b].Diagnosis: Molluscum contagiosum with epidermal cyst.Differential diagnosis: It is necessary to be associated with epidermal cysts, sebaceous gland hyperplasia, pigmented basal cell epithelioma, pigmented cutaneous fibroma and its appendages It belongs to the differentiation of organ tumors, etc.Treatment: Surgical resection.Outcome and follow-up: no recurrence, no similar lesions in other parts.Discussion: MC often occurs, especially in immunodeficient patients (such as malignant tumors, AIDS, etc). For isolated or large skin lesions, it is easy to be confused with other skin diseases in clinic, and differential diagnosis is needed. It should be distinguished from epidermal cysts, pigmented basal cell epithelioma, pigmented dermatofibroma and accessory tumor[2].Conclusion: The clinical manifestations of this patient were atypical manifestations of Molluscum contagiformis. This case emphasizes the importance of histopathology for accurate diagnosis. Therefore, clinicians must be aware that early detection and accurate diagnosis of this situation are crucial for improving the prognosis of patients.Figure 1a:skin-coloured, shiny papules on the wrist (indicated by red arrow)Figure 2a: The epidermis is generally normal, with cystic keratins visible in the dermis(HE X 40)Figure 2b: eosinophilic inclusions visible around the sac wall. (HE X 100)