Mucinous syringometaplasia with prominent epithelial hyperplasia and deep dermal involvement.

This report describes two patients with mucinous syringometaplasia whose findings expand the microscopic and clinical spectrum of the entity. The first patient had an eroded nodule that exhibited multiple epidermal invaginations that penetrated deeply into the dermis. In addition to mucinous metaplasia, there was also exuberant papillary epithelial hyperplasia. Expanded eccrine ducts with similar changes appeared as lobules isolated in the dermis but were shown to connect with the invaginations. In the second patient, a clinical "cyst" drained serous fluid. Multiple papillary-cystic epithelial lobules similar to those seen in the first case were located in the dermis. A few approached the epidermis, but epidermal connections were not identified. The epithelium in these lesions was identical to that previously described in mucinous syringometaplasia. The tumors differed from prior cases by virtue of the number of eccrine apparatus involved, the extent and depth of involvement, and the presence of prominent papillary epithelial hyperplasia.