The scalp is often the first site affected by psoriasis, but scalp psoriasis may be overlooked or treated as other conditions before the correct diagnosis is made and it remains a challenging condition for both clinicians and patients
Psoriasis typically affects the limbs, trunk, buttocks and scalp with variable degrees of severity. Scalp psoriasis can occur alone or in combination with more extensive body disease. In its mild form it can look like excessive scaliness which can be mistaken for seborrhoeic dermatitis (dandruff).
In moderate disease it has the more typical appearance of psoriasis with well defined erythematous plaques of varying number and size, topped with thick silver scales.
A severe variant of scalp psoriasis is known as pityriasis amiantacea which has hard seed-like scales stuck to scalp hairs, forming a thick yellow crust that may bind down the hair. In any type of scalp psoriasis there can be itching or soreness, but it is very unusual to have hair loss. In many patients, scalp psoriasis only affects the hair-bearing scalp and spares any bald areas.
Often scalp psoriasis overlaps with true seborrhoeic dermatitis in condition sometimes called sebo-psoriasis, in which it is thought that the inflammation of seborrhoeic dermatitis induces psoriasis in the same areas via the Koebner phenomenon. Typically the sebo-psoriasis affects the hairline, ears and also the T-zone of the face.
The diagnosis of scalp psoriasis is essentially a clinical one and is usually straightforward when other features of psoriasis are present, but other conditions may have a superficially similar appearance including eczema, tinea capitis, lichen planus pilaris and discoid lupus erythematosus. In such cases a diagnostic biopsy may be helpful
Patients with psoriasis need to be managed on an individual basis according to the severity of the disease and its impact on their quality of life. When scalp psoriasis is the only or the first manifestation of psoriasis, patients who are unfamiliar with the disease often benefit from advice about living with a chronic condition that requires long-term treatment.
Sometimes they need reassurance that it is not contagious or malignant. If the scalp psoriasis spreads onto the forehead or facial sites, it can cause significant psychosocial anxiety and this often adds to the stress of coping with the stigma of skin disease.
An additional challenge in the treatment of scalp psoriasis is the selection of products suitable for hair bearing skin. Ointments and creams may be appropriate for psoriasis on the body, but are rarely the right choice for the scalp.
Other formulations such as lotions, gels, foams and emulsion allow for easier application, however even these treatments may be inconvenient or cosmetically unacceptable to many patients. The feel and smell of the product are important factors to consider when choosing treatment options and it may be necessary to accept that strong smelling or messy products are likely to be used infrequently even though they may be effective.
Compliance with treatment and hence treatment effectiveness is usually better if single products (which may contain several active ingredients) are used.
Emollients, while very important in psoriasis on the body, are messy and difficult to apply to the scalp. They are, however, useful in reducing the redness, dryness and flakiness of the condition. Some patients use natural oils such as olive oil or almond oil to soften any hyperkeratosis. Ointments such as unguentum cocois compound (ung. cocois co.) use coconut oil as the emollient and also have other ingredients with therapeutic effects.
Topical vitamin D analogues such as calcipotriol are currently first line treatments for scalp psoriasis, and, as they do not smell or stain, are more cosmetically acceptable. Vitamin D analogues may cause local skin irritation, but if tolerated can be used intermittently in the long term. Combinations of vitamin D analogues with a topical steroid are also useful.
Corticosteroids such as betamethasone diproprionate are a very important treatment for scalp psoriasis. Preparations suitable for daily use include gels, lotions, foams and even shampoos. In general the topical steroids should be used daily for two weeks and then 2-3 times a week to avoid steroid side effects.
Combining products containing corticosteroids and vitamin D analogues appear to give better results than prescribing them separately. When treating scalp psoriasis with both vitamin D analogues and potent corticosteroids, it is important to avoid the delicate skin of the face.
Mild or mid-potency corticosteroid creams with additional anti-yeast ingredients (eg nystatin, miconazole) are very helpful for sebo-psoriasis and are suitable for facial and flexural sites.
Coal tar is a useful ingredient in shampoos and other scalp therapies. It has anti-itch, anti-scaling and anti-inflammatory properties. Shampoos containing coal tar are best used only once or twice a week to avoid irritating the scalp.
Topical treatments such as shampoo containing coal tar can relieve symptoms of the condition
Other coal tar preparations such as lotions and combination scalp ointments (ung. cocois co.) are helpful, but the challenge remains their strong smell and inconvenience which can be minimised by using them weekly with overnight application so they can be washed out the following morning.
Salicylic acid is a keratolytic agent and is used as an ingredient in shampoos, in some corticosteroid scalp applications and other preparations such as ung. cocois co. It is useful in very scaly scalp psoriasis such as pityriasis amiantacea, but can be irritant if used too frequently.
Dithranol (anthralin) is effective for chronic plaque psoriasis and is more commonly used on the body, but scalp preparations are available. However, its tendency to stain skin, hair and clothes makes it difficult and unpleasant to use on visible areas such as the scalp.
Phototherapy and systemic treatments
Most cases of scalp psoriasis improve with topical agents. If, however, these are ineffective other treatment options need consideration. Phototherapy is rarely used in scalp psoriasis as it is difficult to deliver light to hair-bearing skin.
Acitretin, a vitamin A derivative, has an anti-proliferative effect and is useful in hyperkeratotic scalp disease. Female patients must not become pregnant during or for two years after finishing treatment owing to its teratogenicity.
Ciclosporin, a calcineurin inhibitor, is a potent immunosuppressant and has a rapid onset of action. It is particularly useful in inflammatory scalp psoriasis.
Methotrexate, a folate antagonist, has both immunosuppressive and anti-proliferative actions and is often used in psoriasis where there is also psoriatic arthritis.
In the UK, biological agents are indicated when two systemic agents have failed to control severe plaque psoriasis but are rarely indicated for isolated scalp psoriasis. Products which block tumour necrosis factor (TNF) such as etanercept, infliximab and adalimumab have the longest established clinical experience. Newer agents such as ustekinumab (which blocks interleukins 12 and 23) have yet to prove effective in scalp disease.
Dr Anshoo Sahota is consultant dermatologist at Whipps Cross University Hospital, Royal London Hospital, London and Claire Pearce is a medical student with Barts and The London School of Medicine and Dentistry