On the basis of study of findings histopathologically in 45 patients and features of lesions clinically in 14 of those patients, all of whom had been diagnosed previously as "follicular mucinoses," we endeavored to integrate the data that was collected and what follows is an account of that effort at synthesis.

Despite the fact that the designation "follicular mucinosis" is so well established, we have elected to abandon it in favor of a term that much more accurately captures the essence of the process, namely, epithelial mucinosis. Although so-called follicular mucinosis affects follicles episodically, it much more often affects infundibular epidermis and more often, too, affects sebaceous lobules. In sum, what is called follicular mucinosis is typified histopathologically by deposits of mucin in infundibular, follicular, and sebaceous epithelium, a phenomenon that really is epidermal (infundibular) —follicular — sebaceous mucinosis. That being the case, the findings morphologically are more properly characterized as "epithelial mucinosis," and that is what we have chosen to designate it. Epithelial mucinosis may be encountered as an incidental finding in a host of circumstances, among those being melanocytic nevi, verrucae vulgares, allergic contact dermatitis, rosacea, and "eosinophilic folliculitis," including Ofuji's disease. Epithelial mucinosis is not a criterion for diagnosis of any of these conditions, whereas it is the sine qua non for diagnosis of a singular manifestation of mycosis fungoides known conventionally as "alopecia mucinosa," which, in synchrony with what has just been stated, we will refer to in the remainder of this essay as "mycosis fungoides with epithelial mucinosis." In the ultimate analysis, however, epithelial mucinosis is no more essential to diagnosis of mycosis fungoides than it is to eosinophilic folliculitis; the diagnosis histopathologically turns on findings other than epithelial mucinosis.

It cannot be stressed too emphatically that because mucin in epithelial mucinosis, which ranges in amount from scant to prodigious, is seen mostly in infundibular epidermal and in sebaceous lobular epithelium, it should not be inferred that follicular epithelium itself is not affected by the process sometimes. One reason for the seeming preponderance of mucin in infundibular epithelium, rather than in follicular epithelium, of lesions of mycosis fungoides with epithelial mucinosis is because biopsy specimens of them so often come from the face where infundibula are particularly long to begin with and where they appear even more behemoth than elsewhere because follicles with which they are affiliated are puny vellus ones. On other anatomic sites, follicles, made up as they are always of isthmus, stem, and bulb, all too often appear to be attenuated because in sections of tissue cut routinely they commonly are oriented obliquely. When, however, a terminal follicle in anagen is visualizable along the entire length of it, mucin in epithelial mucinosis may be seen at times in all three parts of it, including the matrix-containing bulb, which accounts for why the alopecia in mycosis fungoides with epithelial mucinosis ultimately comes into being. As can be intuited from perusal of this paragraph, we now eschew the term "alopecia mucinosa" in favor of "mycosis fungoides with epithelial mucinosis," that being done for purposes both of accuracy and of clarity.

Mycosis fungoides with epithelial mucinosis fulfills all criteria for mycosis fungoides clinically and histopathologically, being typified clinically by infundibulocentric papules and/or plugs of horny material and histopathologically by mucin in one or more epithelial structures in skin (Figs. 29–37). When sections of tissue from lesions of mycosis fungoides with epithelial mucinosis are scrutinized for changes in surface epidermis, almost always signs typical of mycosis fungoides can be appreciated there, those often being remarkably subtle, such as very few lymphocytes disposed as solitary units in foci of the basal layer and in the spinous zone in company with spongiosis so paltry or absent entirely that the lymphocytes seem to be inert, and elongated mounds of parakeratosis and/or of scale-crusts. Infundibular and sebaceous epithelium that house mucin is riddled with lymphocytes which, in some instances, may be outnumbered by eosinophils. The infundibulotropism and sebaceotropism of lymphocytes are well known attributes of mycosis fungoides; no epithelium in the skin is free from involvement by lymphocytes of mycosis fungoides, including that which is eccrine ductal (Figs. 36 and 37 ).

As a rule, most of the infundibulofollicular stuctures in a particular section of tissue of mycosis fungoides with epithelial mucinosis are affected overtly by the process, a finding that is useful in differentiation of mycosis fungoides from circumstances in which epithelial mucinosis is encountered as an incidental finding unrelated wholly to mycosis fungoides. In that latter situation, only a single infundibulofollicular structure usually is involved; that also may obtain, uncommonly, for epithelial mucinosis in the setting of mycosis fungoides and of other lymphomas in the skin. Although nearly every infundibulofollicular stucture in a particular section of tissue of mycosis fungoides with epithelial mucinosis is shot through with lymphocytes, not all of those epithelial units contain mucin in abundance. The amount of mucin in affected epithelium varies markedly from slight (Figs. 29 and 30 ) to extraordinary (Fig. 33 ), some sections being punctuated by lakes of mucin, especially in infundibula. When those funnel-shaped aspects of epidermis are filled to the breaking point, it is inevitable that some mucin will be discharged into the reticular dermis, where, in sections stained by hematoxylin and eosin, it can be identified for what it is as granular and stringy basophilic material. It is the presence of copious quantities of mucin in infundibula that is responsible for the oft-noted phenomenon in mycosis fungoides with epithelial mucinosis of sticky material being expressible easily from ostia of infundibula simply by squeezing a lesion between thumb and forefinger.

When infundibula are filled to overflowing by mucin and those epithelial structures rupture, not only is mucin spewed into the dermis, but other infundibular contents such as corneocytes and microorganisms, those elements inducing a granulomatous inflammatory process of foreign body type. This phenomenon of foreign body granulomatous inflammation is not unique to mycosis fungoides with epithelial mucinosis, being present as it is at times in types of mycosis fungoides that range from patches with sparse infiltrates of lymphocytes in foci in the interstitium of the reticular dermis ("interstitial mycosis fungoides") through plaques with more dense infiltrates of lymphocytes and numerous histiocytes, some of them multinucleate and often in the interstitium of the reticular dermis (badly termed "granulomatous mycosis fungoides") to huge pendulous tumors characterized by predominance of histiocytes, an inordinate number of them multinucleate and with a riveting number of nuclei, throughout the dermis and far into the subcutaneous fat ("granulomatous slack skin"). The designations housed in parenthesis in the last sentence are misleading; granulomatous inflammation may develop in patches, plaques, and tumors of mycosis fungoides and always as a secondary phenomenon, to wit, a foreign body reaction. In the usual circumstance, the granulomatous response develops consequent to the effects on elastic fibers of products of neoplastic lymphocytes, the altered elastic tissue being regarded then as foreign bodies by macrophages which proceed to consume them. In the case of mycosis fungoides with epithelial mucinosis, however, the aforementioned foreign body reaction usually is not in play, but rather another kind of foreign body reaction, this time to contents of infundibula that have been discharged into the dermis secondary to collapse of the wall of that epidermal structure because of an overabundance of mucin in it. In brief, all expressions of granulomatous inflammation in mycosis fungoides reflect a response to foreign material; there is no true "granulomatous mycosis fungoides," only mycosis fungoides with secondary granulomatous inflammation.

The infiltrate of cells in mycosis fungoides with epithelial mucinosis may be made up entirely of lymphocytes or of lymphocytes and eosinophils, in different proportions (Figs. 30 –35 ). The inflammatory cells usually are present around venules of both the superficial and deep plexuses, in the interstitium of the reticular dermis, in infundibular, follicular, and sebaceous lobular epithelium, and in the periadnexal dermis. An interstitial pattern in the reticular dermis of mycosis fungoides with epithelial mucinosis may consist of lymphocytes alone, lymphocytes and histiocytes, or lymphocytes and eosinophils. At times, histiocytes or eosinophils may outnumber lymphocytes. The presence of lymphocytes in company with histiocytes in the interstitium of the reticular dermis allows for differentiation of "interstitial" mycosis fungoides from "interstitial" granuloma annulare in which histiocytes tend to monopolize in the interstitium.

Neoplastic lymphocytes of mycosis fungoides tend to be epitheliotropic, not merely epidermotropic, and may penetrate any epithelial structure of adnexa, as well as the epidermis (both surface and infundibular). The effects of the neoplastic lymphocytes on those epithelial structures are mucinosis of infundibulo-folliculo-sebaceous units, hyperplasia of eccrine units, psoriasiform and very slight spongiotic hyperplasia of surface epidermis accompanied often by elongated scale-crusts, and parakeratosis of infundibular epidermis. Lymphocytes within epithelia of eccrine units, especially of ducts, have been dubbed by some authors "syringotropic mycosis fungoides," and "syringolymphoid hyperplasia with alopecia" by others.

Nuclear atypia of lymphocytes need not be present in infiltrates of patches and subtly elevated plaques of mycosis fungoides with epithelial mucinosis; in fact, nuclei of lymphocytes in those lesions hardly ever exhibit impressive atypia. Of course, later in the process, when plaques become demonstrably elevated or when nodules and/or tumors come into being, as they do sometimes in some patients with mycosis fungoides with epithelial mucinosis, not only are atypical lymphocytes to be expected, they may be present in large numbers.

In some section of tissue, infundibula may be altered both by deposits of mucin and by parakeratosis that takes the form of plugs, some of them strikingly conspicuous and sometimes jutting above the skin surface, emanating from widened infundibula whose epithelium became progressively thinned (Figs. 34 and 35 ). Changes like those just described are seen also in so-called follicular mycosis fungoides.