Follicular mucinosis: a detailed morphologic and immunopathologic study.

Two patients with the benign type of follicular mucinosis (FM) are presented. Their clinical features and course were characteristic for this subgroup of FM. Light and electron microscopy, direct immunofluorescence, and immunoperoxidase cell marker studies were undertaken to characterize the nature of the disease process. Light microscopy confirmed the follicular outer root sheath and sebaceous gland epithelial degenerative changes. The infiltrating inflammatory cells were morphologically benign. Electron microscopy detailed the cellular associations in the areas of degenerative change. Disattached keratinocytes were closely apposed to significant numbers of macrophages and Langerhans cells. Direct immunofluorescence studies demonstrated primarily complement (C3) and fibrinogen/fibrin in areas of reticular degeneration. Immunoperoxidase studies revealed large numbers of T cells and macrophages and a striking increase in the number of Langerhans cells in the affected follicular epithelium. The findings suggest that cell-mediated immune mechanisms may play a role in the pathogenesis of this disorder.