Cutaneous mucinoses: microscopic criteria for diagnosis

The clinical aspects and the histologic features of cutaneous mucinoses have been reviewed and their classification updated. Cutaneous mucinoses are divided into distinctive (primary) cutaneous mucinoses in which the mucin deposit is the main histologic feature resulting in clinically distinctive lesions, and disorders associated with histologic mucin deposition as an additional finding (secondary mucinoses). The former are further divided into degenerative-inflammatory mucinoses, which may be either dermal or follicular, and into neoplastic-hamartomatous mucinoses. Histopathologic diagnosis is particularly difficult for dermal mucinoses and requires clinicopathologic correlation. Three histologic clues, namely the pattern of mucin distribution (diffuse or focal), the level of mucin deposit in the dermis and some additional findings may help diagnosis. Follicular mucinoses have the easiest pattern to recognize histologically, but the distinction between Pinkus' follicular mucinosis and follicular mucinosis with mycosis fungoides is very difficult.Lastly, neoplastic-hamartomatous cutaneous mucinoses include mucinous nevus, a benign hamartoma, and myxoma, which is a benign tumor to be differentiated from reactive cutaneous focal mucinosis.