Acne vulgaris, erythematous papule vs. Rosacea, erythematous papule

Differential Diagnosis

Acne vulgaris, erythematous papule Rosacea, erythematous papule 1. Only one follicle involved usually in a 4 mm biopsy specimen 1. Nearly all follicles involved usually in a 4 mm biopsy specimen 2. Suppurative infundibulitis prominent 2. Suppurative infundibulitis and granulomatous peri-infundibulitis prominent 3. Peri-infundibulitis not consequential 3. Peri-infundibulitis often predominant 4. No spongiotic infundibulitis 4. Spongiotic infundibulitis episodic 5. Large abscesses in the dermis sometimes 5. Tiny abscesses in the dermis sometimes 6. Granulomas in conjunction with suppurative inflammation 6. Granulomas often in the absence of suppuration 7. No necrosis in association with granulomas 7. Caseous necrosis sometimes in the center of granulomas 8. Few, if any, lymphocytes or plasma cells 8. Notable infiltrate of lymphocytes and plasma cells 9. Comedones and milia present often 9. No comedones or milia 10. Infundibular cysts and sinus tracts may be accompaniments 10. No infundibular cysts or sinus tracts 11. Telangiectasias not remarkable 11. Telangiectasias often striking 12. Little or no solar elastosis 12. Solar elastosis often abundant

Discussion

Erythematous papules of acne vulgaris and of rosacea have in common localization mostly to the face, suppurative infundibulitis, and a mixed infiltrate of inflammatory cells in the dermis, it containing lymphocytes and plasma cells, and sometimes histiocytes in clusters (granulomas). In times past, rosacea was known as acne rosacea.

Differentiation histopathologic between the two seemingly similar, yet fundamentally different, conditions turns on the fact that acne vulgaris essentially is an infundibulitis, and not a peri-infundibulitis, whereas rosacea is both an infundibulitis and a peri-infundibulitis. Granulomatous inflammation is basic to papules of rosacea, where it tends to predominate in lesions developed fully, whereas in acne vulgaris it is incidental to the suppurative process. Suppuration is common in papules of acne vulgaris where large abscesses in the dermis are accompanied by evidences of a ruptured infundibulum. In rosacea, there are no large abscesses, only small ones, which reflect leakage of contents of infundibula through a rent in the wall of them. Plasma cells tend to be numerous in papules of rosacea, but not in those of acne vulgaris.

The word "acne" derives from Latin "acme" which means a point. Acne vulgaris and "acne" rosacea not only have elevated (gently "pointed") lesions in common, but both favor the middle third of the face in both horizontal and vertical directions, both consist of erythematous papules and pustules, and both are inflammatory diseases of infundibula, i.e., suppurative infundibulitides. Despite these denominators in common, acne vulgaris and rosacea are very different from one another, clinically, histopathologically, biologically, and in response to therapy.

Acne vulgaris, a disease of adolescence primarily, affects the face mostly and, to a lesser extent, the chest, shoulders, and back. Involvement of the trunk tends to be more pronounced near the midline. Acne usually is more severe in men than in women because the mediator of the pathologic process is androgens. Acne vulgaris is manifested morphologically by a variety of lesions, chief among them comedones which are common, but not essential, elements for diagnosis of it. There also may be papules, pustules, and nodules the latter representing infundibular cysts which, on rupture, became inflamed. When the inflammatory process is florid, it may eventuate, in years, in pitted or hypertrophic scars or in tenacious sinus tracts of "acne conglobata."

Comedones traditionally have been described as "open" (blackheads) or "closed" (whiteheads). In actuality, a comedo is simply dilation of an infundibulum as a consequence of its being stuffed by corneocytes mostly. Because all infundibula connect to the skin surface, all comedones really are "open," if only by a micron; none truly is "closed" completely.

The clinical lesions of rosacea are telangiectases, papules, pustules, and nodules. The telangiectatic expression cannot be diagnosed with specificity by histopathologic changes alone because it consists only of sparse superficial perivascular infiltrates of lymphocytes around widely dilated venules. How those changes are related to the papular and rhinophymatous expressions of rosacea is not known.

In rhinophyma, the most dramatic presentation of rosacea, bulbous enlargement of a nose results from tremendous hyperplasia of sebaceous lobules and formation of many infundibular cysts that rupture, thereby sending contents of infundibula into the dermis and inducing suppurative granulomatous inflammation that culminates in scarring. Pustular lesions of rosacea are an expression of suppurative infundibulitis, and fully formed papules of rosacea, devoid of pustules, are granulomas positioned next to infundibula. Nodules are an exaggeration of papules. Rosacea is associated episodically with blepharitis, keratitis, and conjunctivitis, the relationship between the inflammatory process in the skin and in the eye not being misunderstood.

The presence of caseous necrosis in epithelioid tubercles of rosacea led pathologists of former generations to consider it a hypersensitivity reaction to tubercle bacilli, i.e., a "tuberculid." Rosacea-like tuberculid, lupus miliaris disseminatus faciei, and acnitis were wrongly presumed to be forms of tuberculosis. Today, those conditions are recognized to be variants of rosacea and to be unrelated to tuberculosis.

The mechanisms that lead to development of acne vulgaris, although not understood completely, are comprehended better than those that culminate in rosacea. A relationship of testosterone to acne vulgaris is well established and is exemplified by occurrence of acne in newborns and in pregnant women, but not in castrated men. In like manner, acne vulgaris occurs in syndromes in which hirsutism develops as a consequence of an adrenal metabolic defect, an adrenal neoplasm, or a germ cell neoplasm. The precise role of sebaceous secretion and of Propionibacterium acnes in the pathogenesis of acne vulgaris has yet to be defined.

Acne keloidalis is acne conglobata localized to the nape, the changes, clinical and histopathologic, being just like those of perifolliculitis abscendens et suffodiens, known also, and erroneously, as dissecting cellulites of the scalp, and hidradenitis suppuration, which is not hidradenitis truly but explosive suppurative infundibulitis, just as are acne conglobata, acne keloidalis, and perifolliculitis abscedens et suffodiens. In each of those suppurative infundibulitides, sinus tracts develop subsequent to hyperplasia of ruptured infundibular epithelium, which represents an attempt to contain the sea of neutrophils, the process ending in extensive fibrosis manifested clinically by scars and keloids.

Ref:

Differential Diagnosis In Dermatopathology I, Ii, Iii, Iv.chm