Psoriasis is a common papulo-squamous disorder affecting 2% of the population and is characterized by well demarcated, red scaly plaques. The skin becomes inflamed and hyperproliferates at about ten times the normal rate. It affects males and females equally and can affect all races. The age of onset occurs in two peaks. Early onset (age 16–22) is commoner and is often associated with a positive family history. Late-onset disease peaks at age 55–60 years.
The exact aetiology is unknown but evidence suggests that psoriasis is a T-lymphocyte-driven disorder to an unidentified antigen(s).
Chronic Plaque Psoriasis : Clinical Features
This is the ‘common’ type of psoriasis. It is characterized by pinkish red scaly plaques, with a silver scale seen, especially on extensor surfaces such as knees and elbows. The lower back, ears and scalp are also commonly involved. New plaques of psoriasis occur at sites of skin trauma – the so-called ‘Köbner phenomenon’. The lesions can become itchy or sore. Certain drugs can make psoriasis worse, notably lithium, antimalarials and rarely beta-blockers.
Skin biopsy shows epidermal acanthosis and parakeratosis, reflecting the increase in skin turnover, and the granular layer is often absent. Polymorphonuclear abscesses may be seen in the upper epidermis. The epidermal rete ridges appear elongated and clubbed as they fold down into the dermis. Dermal changes include capillary dilation surrounded by a mixed neutrophilic and lymphohistiocytic perivascular infiltrate.
Nails: Up to 50% of individuals with psoriasis develop nail changes and rarely these can precede the onset of skin disease.
There are five types of nail change:
- Pitting of the nail plate
- Distal separation of the nail plate (onycholysis)
- Yellow-brown discoloration
- Subungual hyperkeratosis
- Rarely a damaged nail matrix and lost nail plate.
Treatment of nail dystrophy is very difficult.
Arthritis: Some 5–10% of individuals develop psoriatic arthritis and most of these will have nail changes.
Treatment of Chronic Plaque Psoriasis:
This is concerned with control rather than cure and should be tailored to the patient’s wishes. Severe cases may require hospitalization.
Emollients should always be used to hydrate the skin. Mild to moderate topical steroids, synthetic vitamin D3 analogues (e.g. calcipotriol, calcitriol, tacalcitol), 0.05% tazarotene (a retinoid) and purified coal tar are the most popular therapies. Salicylic acid can be a useful adjunct. All should be applied once to twice daily to palpable lesions. Once lesions have flattened, therapy can be discontinued. Tazarotene and calcipotriol can be very irritant (calcitriol somewhat less so) so they are often used in combination with steroid creams. Vitamin D analogues should be used with caution in extensive psoriasis because there is a risk of hypercalcaemia if greater than 100 g is used per week.
Dithranol causes staining of the skin and clothing and is more difficult to use at home on a regular basis. It is normally applied for 20–60 min and then washed off. It must be applied carefully to the lesions as it causes irritation to normal skin. Dithranol is more likely to induce remission than other therapies but is being recommended less because of poor compliance.
Topical therapies are sometimes used in combination with UVB or PUVA. The ‘Goeckerman regimen’ consists of tar and UVB; the ‘Ingram regimen’ consists of dithranol and UVB. The latter has similar results to oral PUVA in terms of clearance rates and lengths of remission – approximately 75% in 6 weeks.