Sebopsoriasis

Sebopsoriasis is an overlap of seborrhoeic dermatitis and psoriasis, with well demarcated erythematous plaques that bear greasy yellow scale on the scalp, face and other seborrhoeic sites. It shows features of both disorders.

It is most frequent in adults, with a male predominance, and is more common and more severe in HIV infection and in Parkinson disease. Exact prevalence is uncertain, since it is often classified as one or other disease.

The yeast Malassezia and an altered inflammatory response to it are implicated. Cold, dry weather, stress, alcohol and heavy skin occlusion aggravate it, and the course is chronic and relapsing.

Pathophysiology.

Malassezia lipase activity releases irritant fatty acids on sebum rich skin. In susceptible people this triggers a mixed inflammatory response with psoriatic features (helper T-cell type 17 activity), keratinocyte hyperproliferation and greasy scale.

• Erythematous, well defined plaques with greasy yellow scale on the scalp, eyebrows, glabella, nasolabial folds, retroauricular area, central chest and flexures.
• Extension beyond the hairline, unlike simple seborrhoeic dermatitis, with thicker plaques than are usual in seborrhoeic dermatitis.
• Mild to moderate itch, with scalp scale and occasional hair thinning.
• Psoriasis at other sites in some, with nail pitting.

• Clinical diagnosis from the distribution and mixed morphology.
• Potassium hydroxide microscopy and culture to exclude tinea capitis or tinea faciei.
• HIV test when disease is severe, sudden or atypical, and other tests by the history.
• Skin biopsy for diagnostic doubt: psoriasiform dermatitis with spongiosis, parakeratosis and follicular plugging.

Differential diagnosis. Seborrhoeic dermatitis, plaque psoriasis of the scalp, tinea capitis, atopic dermatitis, rosacea, cutaneous lupus, dermatomyositis, pemphigus foliaceus and contact dermatitis.

Scalp.

• Ketoconazole 2% shampoo twice weekly for 2 to 4 weeks, then once weekly or every 2 weeks, with zinc pyrithione or selenium sulphide as alternatives.
• Salicylic acid 2 to 5% or coal tar shampoo for scale. For thick plaques, apply salicylic acid in an oil base and remove after several hours.
• Clobetasol propionate 0.05% shampoo for 15 minutes once daily for up to 4 weeks, or betamethasone valerate 0.1% scalp application once or twice daily, then reduce to intermittent use.
• Calcipotriol 50 micrograms/g scalp solution or the combination with betamethasone, once daily for up to 4 weeks.

Face and body.

• Ketoconazole 2% cream twice daily for 4 weeks, with hydrocortisone 1% cream once daily for up to 1 to 2 weeks for inflamed areas.
• Tacrolimus 0.1% ointment or pimecrolimus 1% cream twice daily for maintenance on the face (off label).

Severe or resistant disease.

• Narrowband ultraviolet B, and for severe psoriasis components, plaque psoriasis treatment with methotrexate 7.5 to 15 mg once weekly (maximum 25 mg) with folic acid 5 mg weekly or biologic therapy.
• Itraconazole 200 mg daily for 7 days, then monthly pulses, is used rarely in resistant disease, with liver monitoring and interaction checks.

Monitoring. Review at 4 weeks. Reduce steroid use when controlled, with maintenance antifungal shampoo.

Referral and escalation. Refer to dermatology for resistant or severe disease, or suspected HIV-associated disease.

Special groups. In HIV infection treat the infection, and disease usually improves with immune recovery. Use mild preparations on the face and in children.