Follicular mucinosis: A detailed morphologic and imrnunopathologic study Harold A. Lancer, M,D., Ben R. Bronstein, M.D., Hidemi Nakagawa, M.D., Atul K. Bhan, M.D,, and Martin C. Mihm, Jr,, M,D, Boston, MA 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 ceils in the affected follicular epithelium. The findings suggest that cell-mediated immune mechanisms may play a role in the pathogenesis of this disorder. (J AM ACAD DERMATOL10:760-768, 1984.) Follicular mucinosis is a general term used to describe a reactive disease process characterized histopathologically by mucin deposition in hair follicles and sebaceous glands that are undergoing epithelial reticular degeneration, t;' This process may occur as a primary disorder or it may be as- sociated with benign (e.g., angiolymphoid hy- perplasia) '~ or malignant diseases (e.g., mycosis fungoides). 4-6 In those cases associated with other disease states, the cutaneous lesions clinically have the appearance of those seen in the primary disease, From the Departments of Dermatology and Pathology (Dermatopa- thology and Irnmunopathology Units), Massachusetts General Hospital, and Harvard Medical School, Supported in part by United States Public Heatth Service Grants Nos. CA29601 and HLt8646, Accepted for publication Sept. 2B, 1983, Reprint requests to: Dr. Martin C. Mihm, Jr,, Dermatopathology Unit, W,'uTen 8, Massachusetts General Hospital, Boston, MA 02114. 760 Alopecia mucinosa is the term used to describe those cases occurring without clinical or his- topathologic evidence of associated disease (pri- mary follicular mucinosis). In such cases, the le- sions clinically appear as minimally scaling, erythematous plaques having prominent follicles. On the hair-bearing skin of the scalp or face, alopecia is a prominent feature. The pathogenesis of FM is unknown. In an at- tempt to further define the nature of the disease process, we employed refined morphoIogic and immunohistochemical technics to study two pa- tients with the clinically benign form, so-called alopecia mucinosa. CASE REPORTS Case 1 A 34-year-old white woman was first seen in the dermatology clinic at the Massachusetts General Hospi- tal in December, 1981, for evaluation of progressive,