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Seborrhoeic dermatitis

Seborrhoeic dermatitis

Seborrhoeic dermatitis is a skin eruption characterised by erythema and scaling. It is most common on the scalp and face but can also involve the upper trunk and flexures including axillae, groin, scrotum and anus. It is more common in patients with neurological disease such as Parkinson’s disease and in human immunodeficiency virus (HIV) infected patients. In HIV-infected patients it is more severe and may have unusual features.

Facial involvement is mostly on the medial cheeks, nose and nasolabial folds. It is by far the most common cause of a ‘butterfly’ rash. Involvement of the medial eyebrows can help to make the diagnosis. It can be difficult to differentiate between psoriasis and seborrhoeic dermatitis of the scalp but in practical terms the treatment is essentially the same. Psoriasis has more sharply defined plaques, and the scale is more silvery and thicker than in seborrhoeic dermatitis.

Seborrhoeic dermatitis on the face and trunk shows well-defined erythema and a greasy scale. It can be difficult to diagnose in the flexures because of loss of scale but shows well-defined erythema. The diagnosis is supported by the presence of the more typical signs that can be observed on the scalp. Unlike psoriasis, seborrhoeic dermatitis does not occur on the elbows and knees, is not associated with an arthropathy, does not have a pustular form and does not affect the palms and soles.

Recent evidence suggests that the pityrosporum yeast is an aetiological factor and this is the rationale for treatment with ketoconazole.

Infantile seborrhoeic dermatitis is a different condition to the adult disease of the same name.

It should be explained to the patient that the treatment is for control of the disease rather than being curative. A response to treatment should be expected within 2 to 3 days. The course is variable with periods of activity and inactivity. Topical corticosteroids are used for their anti-inflammatory effect but ketoconazole also has anti-inflammatory and antiandrogenic actions, which lead to an improvement in the condition. Zinc pyrithione and selenium sulfide have activity against pityrosporum yeast. Coal tar, dithranol and the tetracyclines have anti-inflammatory activity. Salicylic acid, cetrimide and sulfur are used for their keratolytic and descaling properties.

First-line therapy consists of shampoos used at a frequency of once weekly to daily, depending on severity and response. Suitable shampoos include

zinc pyrithione 1% OR selenium sulfide 2.5% shampoo

OR

ketoconazole 1 or 2% OR miconazole 2% shampoo

OR

coal tar 0.5 to 2% shampoo

OR

cetrimide 40% shampoo, diluted 1 part in 20 parts of water before use.

The shampoos need to be left in contact with the scalp for at least 5 minutes before rinsing. Tolerance may develop, and change from one shampoo to another can be useful. If control is not achieved with a shampoo then topical treatment with a longer contact time is needed. The frequency of use is determined by the degree of control. Appropriate preparations are usually applied at night and shampooed off in the morning. Scalp lotions or gels are easier than creams to apply to hair-bearing areas. Use

ketoconazole 2% cream

OR

betamethasone valerate 0.1% OR betamethasone dipropionate 0.05% OR mometasone 0.1% lotion

OR

liquor picis carbonis (LPC) 10% and salicylic acid 6% in sorbolene cream

OR

dithranol 0.1 to 2% in a washable base

OR

salicylic acid 30% in mineral oil left on for 10 to 30 minutes prior to attempting to comb out the scale with a fine tooth comb

OR

sulfur 3 to 5% in sorbolene cream.

Potent corticosteroids should be avoided on the face. The only corticosteroid that is safe to use is hydrocortisone. However, more potent corticosteroids may be used intermittently for up to 2 weeks, but the greater the potency the greater the risk of local adverse effects, particularly perioral dermatitis.

Initial treatment is with

hydrocortisone 1% OR ketoconazole 2% cream applied once or twice daily.

Hydrocortisone is preferred when the dermatitis is more inflamed, itchy or tender. Ketoconazole cream is useful, especially for long-term control, but may be irritating when used on acute dermatitis. It is worthwhile calming moderate to severe seborrhoeic dermatitis with a topical corticosteroid before using ketoconazole cream.

An alternative treatment is

sulfur 2% in sorbolene cream applied once or twice daily.

Very weak tar creams can be used in patients who do not have a sensitive skin.

LPC 1 to 2% in aqueous cream applied to affected areas once daily.

In severe cases, use

tetracycline 250mg orally, 6-hourly OR doxycycline 50 to 100mg orally, daily OR minocycline 100 to 200mg orally, daily.

Treatment is with

a mild or moderately potent topical corticosteroid applied once or twice daily

OR

ketoconazole 2% cream applied once or twice daily

OR

LPC 3 to 6% and salicylic acid 3 to 6% in aqueous cream applied once or twice daily.

Topical corticosteroids, and ketoconazole cream are used. If the condition is severe, moderately potent to potent corticosteroids may be used for short periods (1 to 2 weeks), but for long-term use low-potency corticosteroids should be used to prevent the development of striae.

If corticosteroids are used long-term then topical therapy with an antifungal agent (other than ketoconazole) may be added to prevent secondary infection with Candida, see Candidiasis.

Cleansing with a tar preparation is worthwhile.

This is an under-diagnosed condition and is a common cause of a red scrotum. Treatment is the same as for flexural seborrhoeic dermatitis.

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