Psoriasis is a chronic skin condition, primarily characterised by scaling and inflammation (1) with a prevalence of 1.5% of the total population in the United Kingdom (2). Psoriasis has been known to present at any age, ranging from newborns to elderly patients. However, a bimodal age of onset has been found by numerous large studies, demonstrating that the mean age of first presentation of this disease can range from 15-20 years of age, with a second peak at 55-60 years of age (3).
It is thought that this condition has both genetic and environmental components implicated in its aetiology, but the proportion of genetic as opposed to environmental contribution is not entirely clear (4).
In terms of histopathology, psoriasis tends to show epidermal hyperplasia with varying degrees according to severity. Other histological signs range from tortuous and dilated papillary blood vessels, neutrophils within the epidermis with spongiosis and more keratinocytic mitotic figures above the basal cell layer (5).
Figure 1 – histopathology of plaque psoriasis(6)
The following histological signs of plaque psoriasis are labeled in figure 1 above (6):
1. Hyperkeratosis and parakeratosis
2. Neutrophils in epidermis
3. Thinning of epidermis overlying dermal papillae
4. Vessels close to epidermis
5. Elongated rete ridges
Clinically, psoriasis is a disease with variable morphology, distribution, severity and course. This condition is generally categorised by scaling papules and plaques. Lesions of psoriasis can be differentiated from other conditions as they are classically circular, very well circumscribed red papules/plaques with a grey, dry scale. Other diagnoses to consider include fungal infections, lichen planus and pityriasis rosea. Typically, psoriatic lesions are symmetrically distributed on the extensor surfaces of elbows and knees in addition to the scalp. This condition is also known to exhibit Koebner’s phenomenon. In advanced cases of psoriasis, the disease may manifest itself in nail changes, especially if the skin psoriasis co-exists with psoriatic arthritis (3).
Psoriasis may involve mucosal surfaces or the tongue. There are numerous different types of psoriasis, including small tear shaped papules (guttate psoriasis), pustules (pustular psoriasis), generalised erythema and scale (erythrodermic psoriasis) and chronic plaques (plaque psoriasis). These lesions can present symptomatically with burning or pruritus (3).
Figure 2 – Symmetric psoriatic lesions on elbows and back(3)
Chronic plaque psoriasis is the most common form of psoriasis (3), and while most diagnoses are clinical, a skin biopsy may confirm the diagnosis in some cases (7). More than 80% of patients of patients who suffer from psoriasis have chronic plaque psoriasis (8).
Generalised pustular psoriasis is very rare and is an indication of active, unstable disease. This may be caused by infection or the discontinuation of potent topical corticosteroids. Clinical features include pyrexia, with red, painful, inflamed skin studded with monomorphic, sterile pustules. This cohort of patients are likely to need repeated admissions to hospital (3).
Guttate psoriasis is known to have a better prognosis than other kinds of psoriasis (9). Guttate psoriasis is a condition, which involves an acute onset of 2-10mm diameter circular lesions of psoriasis. Classically, this infection follows an episode of bacterial tonsillitis and accounts for about 2% of all psoriasis. This subtype tends to be self-limiting (3).
Erythrodermic psoriasis is a severe form of psoriasis, which can occur either acutely, or consequent to a chronic course. This subtype is characterised by total or subtotal involvement of the skin by active psoriasis. Erythroderma may impair the thermoregulatory capacity of the skin (3). Numerous treatment options are available and vary according to the disease severity and the patient’s co-morbidities. While all patients should receive potent topical steroids, there are many oral drugs which have been trialled including acitretin, methotrexate, etanercept and infliximab. Combination therapy has also been considered in some cases, yet there is limited literature suggesting an optimal treatment algorithm (10). The NICE Guidelines recommend that any patient with erythrodermic psoriasis should have same-day specialist review and treatment (11).
Topical treatment of psoriasis is considered first-line in all patients according to NICE Guidelines. For psoriasis affecting the trunk and limbs, a potent corticosteroid should be applied once daily with either vitamin D or a vitamin D analogue also being applied once daily. It is important that these two treatments should be applied separately. This tends to be for a period of 4 weeks but can extend to 8 weeks depending on the severity of the condition and the response to treatment. This can then be escalated to applying both vitamin D and a potent corticosteroid twice daily for up to 4 weeks. Alternatively a coal tar preparation can be applied once or twice daily as a substitute for the potent corticosteroid. Calcipotriol monohydrate and betamethasone dipropionate should be applied once daily as a next step. If the psoriasis persists despite all this treatment, specialist opinion should be sought, as a dermatologist should be the only person to prescribe very potent steroids under a supervised environment (11).
Corticosteroids that are potent or very potent should be used with caution, as it is known that they may cause irreversible skin atrophy and striae, unstable psoriasis, or even systemic side effects (11)(12).
For scalp psoriasis, a potent corticosteroid should be applied once daily for up to 4 weeks as first line treatment. Patient education is important in showing them how to apply this correctly. If the problem persists, topical agents containing salicylic acid, emollients and oils may be used before the application of the corticosteroid. A combined product of calcipotriol monohydrate and betamethasone dipropionate may then be used if the problem continues to persist and then a specialist opinion should be sought (11).
Face, flexures and genitals affected with psoriasis should be treated with short term mild or moderate potency steroids (11).
NHS Tayside guidelines state that phototherapy is now the treatment of choice for moderate to severe psoriasis. It also notes that UV light does not help every case of psoriasis and the treatment should be closely supervised. For this reason, phototherapy (narrow-band UVB and PUVA) is highly effective (13).
Systemic therapy is a treatment option for patients with severe or refractory psoriasis. Oral methotrexate, Ciclosporin or acitretin may be used following a detailed discussion of benefits and risks. Acitrenin is a retinoid and should only be prescribed by a consultant dermatologist. As it is Teratogenic, it should be avoided in women of childbearing age unless effective contraception is practiced. When prescribing this difficult drug, regular monitoring in the dermatology clinic must occur (13).
Overall, psoriasis is a relatively common skin condition, which can present in numerous different ways. It is important as any healthcare professional to be aware of the clinical features of psoriasis and the treatment, as well as the red flags, which would prompt specialist referral. Most patients with psoriasis are treated within primary care (14), but patient education is of paramount importance, as knowledge of their condition will ultimately result in better compliance of their medication and overall better care for the patient and their skin condition.
Figure 3 below is an overall representation of the psoriasis and psoriatic arthritis care pathway as detailed by the SIGN Guidelines. This provides an overview, which can guide healthcare professionals towards optimum treatment for the patient (15)