It cannot be emphasized too strongly that when sections of tissue display findings of epithelial mucinosis in conjunction with a mixed-cell infiltrate situated around and within infundibulosebaceous units, all-too-often a specific diagnosis cannot be rendered with surety based on attributes histopathologically alone. Deposition of mucin in infundibulosebaceous epithelium is a distinctive pattern that occurs incidentally in no small number of conditions. We have encountered epithelial mucinosis histopathologically in sections of warts, allergic contact dermatitis, rosacea, "eosinophilic folliculitis," including Ofuji's disease. Common to all of those conditions, in that particular circumstance, is the presence of epithelial mucinosis, but differentiating them histopathologically are all of the other findings. Histopathologically, (and clinically), eosinophilic folliculitis and mycosis fungoides could not be more dissimilar from one another. Yet for 50 years they have been "lumped" together as "alopecia mucinosa." In order to come to a specific diagnosis in these circumstances, clinico-pathological correlation is indispensable. When, however, lymphocytes predominate, when the infiltrate is both periadnexal and interstitial, especially when it is dense and deep, when lymphocytes are present in company with scant spongiosis in the epidermis, and when features clinically are those of slightly reddish and slightly scaly patches and plaques that, in time, come to be studded with infundibulocentric papules, a diagnosis then can be made with confidence of mycosis fungoides with epithelial mucinosis.

In sum and in short, the same criteria for diagnosis histopathologically should be employed for mycosis fungoides with epithelial mucinosis as for mycosis fungoides without epithelial mucinosis. The involvement of epithelial structures by mucin is a helpful clue to a histopathologist that attention should be directed to the possibilities of mycosis fungoides and eosinophilic folliculitis especially.