Molluscum contagiosum: histologic patterns and associated lesions. A study of 578 cases.

Molluscum contagiosum (MC) is rarely associated with other skin diseases, especially cutaneous neoplasms. Such associations are exceptional and of unknown frequency. The aim of this study was to record the histologic variants and frequency of associated lesions in a large series of consecutive MC cases. We reviewed 578 MC cases from the Laboratory of Dermatopathology of the University Hospitals of Strasbourg, France (1959-1999). The locations of MC were as follows: head and neck (34.7%), trunk (27.1%), lower limbs (20.7%), upper limbs (8.7%), and genitalia (3.8%). Molluscum contagiosum occurred more often in female patients (56.7%). The age range of patients included in this study was 0 to 19 years (34.9%), 20 to 39 years (31.1%), 40 to 59 years (22.8%), and over 60 years (6.5%). Histologic variants of MC were noted in 46 cases (31 pseudocystic, 8 giant, and 7 pedunculated). An underlying abscess was present in 65 cases. Of the 578 cases, 22 were associated with other lesions (3.8%). There were 9 cases of epidermal cysts, 4 of nevocellular nevi, 3 of metaplastic ossifications, 2 of true epidermal nevi, 2 of sebaceous hyperplasias, 2 of soft fibromas, and 1 of Kaposi sarcoma. Except in immunocompromised patients, such associations are likely to be coincidental. The clinical diagnosis was correct in 42.3% of the cases. Clinical accuracy varied according to the age, localization, and histologic pattern of MC. Pseudocystic MC, giant MC, and MC associated with other lesions were responsible for frequent clinical misdiagnosis.