Ointments are the preferred vehicle because of better medicine penetration and support of the skin moisture barrier; however, ointments are not easily tolerated by the patient, especially if large skin surface areas are involved. Creams can be prescribed for patients who cannot tolerate ointments. Newer foam-based delivery systems provide advantages for some skin surfaces, such as the scalp, but they are expensive and often nonformulary. Solutions are available that are good vehicles for delivery of medicine to the scalp. Tolerance to steroid preparations rarely develops with plaque psoriasis, which can tolerate chronic application of high doses of steroids, but atrophy can occur with use on thinner lesions, as with inverse psoriasis. Occlusion with clear plastic wrap can increase the efficacy of therapy on large or thick plaques.
For severe, recalcitrant cases, intralesional injections with a corticosteroid suspension produce satisfactory results after one or two injections; this treatment requires a dermatology referral. Limitations of this therapy include atrophy and obvious discomfort from injections.
Scalp psoriasis is often characterized by thick scale, which not only produces embarrassing dandruff but interferes with the steroid's ability to penetrate the dermis. Scalp lesions also respond best to topical high-potency steroids. Combination therapy using vitamin D analogues in conjunction with topical steroids may also be helpful in the treatment of scalp lesions.
Research suggests that coal tar preparations may not be any more effective than placebo in treating scalp lesions. 6 Shampoos containing the exfoliant salicylic acid are available to reduce scale buildup and to improve medication penetration. Use of topically applied mineral oil or vegetable oil and a bathing cap at bedtime is sometimes very effective at loosening and removing scale.