Distribution: scalp, eyebrows, and other hairy areas, nasal folds, glabella, retroauricular folds, external os of the ear, and midsternum
Seborrheic dermatitis is particularly likely to occur in areas where moisture is easily trapped. Thus it most often affects hairy regions and intertriginous folds. The most common of these areas are listed above under diagnostic hallmarks.
In hairy areas seborrheic dermatitis is characterized by the presence of diffuse, poorly marginated plaques of scaling erythema. The scale is often compacted against the underlying skin by the anchoring effect of the hair shafts. In such instances the scaliness will not be appreciated until the involved area is scraped with a fingernail. In very young infants, scale buildup may be extensive enough to deserve the colloquial term "cradle cap." When the scalp is involved, oiliness (seborrhea) of the scale may be noticeable, but in the other locations this is not a prominent finding. In men, seborrheic dermatitis sometimes occurs in the beard, mustache, and hairy area of the midsternum.
Evidence of epithelial disruption is usually not prominent. Pruritus is usually present, but few excoriations are found. Often the only clue to the presence of epithelial disruption is the yellow color of the overlying scale. This yellow color occurs because of small amounts of serum that have exuded onto the surface of the scale. Frank crusting, with less prominent scale formation, occurs in patients with more severe disease.
Seborrheic dermatitis of the scalp must be distinguished from tinea capitis and psoriasis. In these two latter diseases, sharply marginated individual plaques are found, rather than diffuse involvement. Notable hair loss occurs with tinea capitis, but this is not the case in psoriasis or seborrheic dermatitis. In both psoriasis and seborrheic dermatitis, extension onto the nonhairy, marginal skin surrounding the scalp is occasionally seen.
Seborrheic dermatitis also occurs on nonhairy (glabrous) skin. It is particularly likely to be found in the retroauricular folds, the external os of the ears, the nasal fold, and the glabella. Less commonly, intertriginous areas such as the inframammary and inguinal folds may be involved. Generally, seborrheic dermatitis in these areas can be considered as an eczematous variant of intertrigo.
The plaques of seborrheic dermatitis occurring on glabrous skin are often rather sharply marginated and for this reason are easily mistaken for papulosquamous lesions. Confusion with psoriasis is particularly likely, and the terms "seboriasis" and "sebopsoriasis" are sometimes used when differentiation is not possible.
Course and Prognosis
Seborrheic dermatitis is a chronic disease characterized by lnbations and remissions. It can occur at any age. In infancy it is frequently seen as "cradle cap" and as one form of diaper dermatitis . Seborrheic dermatitis is not very prominent during the childhood years, but it frequently develops in the early teens sat the onset of puberty.therafter, it can occur at any time throughout adult life.The acute onset of what appears to be severe seborrheic dermatitis of the face can occur as one of the manifestations of acquired immunodeficiency syndrome (AIDS).
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