Hypopigmented common blue nevus.

Blue nevus is a benign pigmented lesion of dermal melanocytes with a number of histologic and clinical variants, of which the major types are the common blue nevus, cellular blue nevus and combined nevus. This study describes 9 cases of hypopigmented blue nevus (HBN), a variant of common blue nevus in which there is minimal identifiable melanin pigment. We also discuss the usefulness of the immunoperoxidase stain HMB-45 in relation to the diagnosis of HBN and the lesions with which it may be histologically confused, namely common intradermal nevus, dermatofibroma, neurofibroma, dermal scar and desmoplastic malignant melanoma. The HMB-45 stain was found to be uniformly positive in all 9 cases of HBN, in contrast to the other dermal lesions which have been reported as either negative or showing only focal positivity. The physical distribution and age range of the patients in this study was similar to the age and sites for common BN, supporting the relationship between the 2 lesions. The occurrence of HBN in predominantly young adults indicates that this lesion is not a phenomenon due to ageing or degenerative change, and should be regarded as a variant of common blue nevus.