White : Diseases of the Skin - Eczema and Related Disorders

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Gary M. White & Neil H. Cox

Diseases of the Skin

6	Eczema and Related Disorders

SEBORRHEIC DERMATITIS

Etiology and pathogenesis
This is a very common dermatosis, mainly affecting the face and scalp. It is probably the single most common scalp problem for which a patient seeks medical attention. While the hair is normal, the scalp is scaly and mildly erythematous. Seborrheic dermatitis is also common on the oily areas of the face (e.g. the nasolabial fold and eyebrows). Diffuse, ﬁne, non-inflammatory scaling of the scalp (pityriasis capitis or dandruff) is also a form of seborrheic dermatitis. If there is both scaling and erythema, the term seborrheic dermatitis is used.


Fig. 6.78 Seborrheic dermatitis in the axillary fold in a child.

    The leading theory as to the cause of seborrheic dermatitis is that the fungus Pityrosporum ovale (Malassezia furfur) overgrows and causes irritation of the skin. It may do this directly or by secretion of a toxin or other mediator. This irritation causes hyperproliferation, scaling, and erythema of the skin, i.e. an eczematous response. Infrequent shampooing is thus a contributing factor as it allows overgrowth of P. ovale, and antifungal ‘medicated’ shampoos help by reducing the numbers of P. ovale.
    Seborrheic dermatitis occurs in a high percentage of HIV-positive patients. Whether Pityrosporum occurs in higher numbers in such patients or whether the immune system responds abnormally to its presence is unclear.
    Seborrheic dermatitis of the face is commonly exacerbated by cold and dry air, as is typical for other eczematous conditions.

Clinical
Erythema and scale may affect the scalp (Fig.6.72), the ears (including the external auditory canal, causing otitis externa), the nasolabial folds (Fig.6.73), the glabella, the eyebrows (Fig.6.74), and even the entire face (Fig.6.75). Patients often have an oily complexion, thus the term seborrhea. Men with a beard or hairy chest (Fig.6.76) may develop seborrheic dermatitis in these areas. Sometimes the rash may extend to the mid-back, eyelid margin (seborrheic blepharitis), axillae, gluteal cleft, perianal area, and umbilicus.
In black skin, the scaling is prominent but the erythema may be masked (Fig.6.77). Often, postinflammatory hypopigmentation is seen. Sometimes, the changes of seborrheic dermatitis in the black patient blend with lesions of tinea versicolor on the neck and upper trunk.

Differential diagnosis
This will depend on the site affected; discussion is limited to the commonest face and scalp sites.
For the scalp, the following should be considered.

•	Other patterns of dermatitis—AD and contact dermatitis may affect the scalp.
•	Psoriasis—the scale of scalp psoriasis is usually much thicker and may often be hyperkeratotic.
•	Pityriasis amiantacea—this is a description of asbestosis-like scalp scaling for which there are many causative conditions, of which seborrheic dermatitis is one. The scales are larger than in typical seborrheic dermatitis, forming white adherent plates.
•	Pityriasis rubra pilaris—this may start in the scalp as a red, scaly rash but quickly progresses to other areas of the body.
•	Lupus erythematosus—may produce redness and scaling,usually well demarcated. The redness tends to be perifollicular, and scarring often ensues.
•	Lichen planus—perifollicular redness, often rather purple in color, and follicular scaling.
•	Dermatophyte fungal infection—rarely affects scalp, other than with cattle ringworm; it is more localized than typical seborrheic dermatitis, and may have a pustular component.
•	Dermatomyositis—scalp redness and scaling are probably underestimated.


Fig. 6.79 Diffuse seborrheic dermatitis in a child.

For the face, the following should be considered.

•	Other patterns of dermatitis—AD (usually whole face or sites of rubbing such as the eyelids) and contact dermatitis (many patterns). Contact dermatitis may be localized to eyelids, ears, etc. but does not usually have the ‘full house’ of sites affected by seborrheic dermatitis.
•	Psoriasis—facial involvement is common and tends to correlate with severity, but rarely occurs in the absence of psoriasis at other sites. Scalp margin and ears are often affected. Some patients seem to have an overlap condition sometimes termed sebopsoriasis.
•	Pityriasis rubra pilaris—facial involvement occurs at an early stage.
•	Rosacea—a common mid-facial rash, mainly affecting cheeks, chin, and central forehead rather than nasolabial folds and scalp margin. Involvement of the scalp and ears would not be expected, and the rash has papules and pustules. However, it can be difﬁcult to distinguish and may coexist in some individuals, as both are common conditions.
•	Lupus erythematosus—discoid lupus erythematosus may produce redness and scaling of individual areas such as the ear or eyebrow. Systemic lupus erythematosus is in the differential of mid-facial (butterfly) rash but affects the cheeks rather than the nasolabial folds, and is associated with systemic symptoms.
•	Dermatophyte fungal infection—uncommonly affects the face; if it does, then it is typically asymmetric.

Treatment
For the patient who shampoos only once a week, shampooing daily or every other day may be sufﬁcient. Otherwise, daily use of a medicated shampoo (e.g. selenium sulﬁde 2.5%, zinc pyrithione, and tar) is recommended. One of the best shampoos is ketoconazole (Nizoral shampoo), which contains an imidazole antifungal agent to kill Pityrosporum yeasts. It is highly effective and more cosmetically acceptable to patients than more abrasive tar shampoos. Use of any of these shampoos may be followed
by the use of another shampoo or conditioner of the patient’s choice. Ketoconazole 1% shampoo is available over the counter; although less effective than the 2% solution, it is helpful in mild cases.
    If itching of the scalp is a persistent problem, a topical steroid should be added (e.g. betamethasone diproprionate solution, triamcinolone 0.1% lotion, and fluocinonide solution) or, in the most stubborn cases, clobetasol propionate solution. Alternatively, fluocinolone 0.01% shampoo (patients lather the scalp, leave 5 min, and rinse daily) is very effective at clearing the itch. For the rare patient with a persistent lesion in the same area of the scalp, excessive scratching may be a contributing cause.
    When seborrheic dermatitis is present on the face, the patient can lather the face daily or every other day with the medicated shampoo or can use topical ketoconazole cream. A topical steroid (e.g. hydrocortisone 1% cream) is usually recommended as well to treat the eczematous response; for convenience, a combined imidazole–hydrocortisone preparation may be used.
    For seborrheic dermatitis of the eyelids, daily gentle shampoo with ketaconazole shampoo (or baby shampoo if irritation occurs) should be tried. For lid margin seborrheic blepharitis, carefully apply combined miconazole–hydrocortisone cream to the base of the lashes from the cutaneous rather than from the mucosal aspect: imidazoles are irritant to the conjunctiva. For seborrheic dermatitis of the ear, a low-potency topical steroid or imidazole–corticosteroid combined product applied twice a day for the pinna and a corticosteroid otic preparation for the ear, are effective. Daily use of a medicated shampoo is also recommended.
    Due to the hair type of most African-Caribbean patients, medicated shampoos (e.g. ketaconazole 2% shampoo) should be recommended and the patient instructed to let the shampoo sit on the scalp (contact with the hair is not necessary) for approximately 15–20min twice a week. For those with signiﬁcant itching or inflammation, a topical steroid should be added. A steroid ointment applied after shampooing is usually best, and is appropriate for any type of hair: processed or hot-combed. It may also be used as a substitute for hair oils.

PRACTICE POINTS

•	Always ask the patient with seborrheic dermatitis how often they shampoo and if they shampoo their face. It may be helpful to tell them they have ‘dandruff of the face’ to help motivate treatment.
•	Stress the need for using a medicated shampoo daily or every other day. Many patients will paradoxically shampoo less often, as they think they are irritating the skin.
•	For best results in seborrheic dermatitis, treat both the causative yeast (with topical imidazole) and the eczematous response (with hydrocortisone).