Psoriasis is a common, chronic inflammatory disease of the skin, characterized by erythematous papules and plaques surmounted by silvery white scale.
Aetiopathogenesis
The disease can involve any group but peak incidence is seen in between 15-40 years. Both sexes are equally affected. Exact aetiology is unknown, probably it is multifactorial. The genetic basis of psoriasis is based on the familial incidence of psoriasis and increased prevalence of certain HLA antigens. Certain provocating factors like trauma, infection, emotional upset, climate changes, drugs and hormonal variation may precipitate or exacerbate the disease.
The characteristic pathophysiological event in psoriasis is increased epidermopoiesis. The increased level of cyclic GMP and variable level of cyclic AMP have been found in psoriasis lesions. Immunological phenomenon may take part in the pathogenesis of the disease.
Pathology
Histology is characterized by :
- Parakeratosis and acanthosis
- Elongation of rete ridges
- Broadening of lower ends of ridges
- Thinning of suprapapillary portion
- Elongation of dermal papillae
- Oedema and dilated capillaries in upper dermis
- Presence of munro-microabscesse
Clinical Features
The lesions are asymptomatic or mildly itchy, erythematous papules and plaques covered with loosely adherent silvery scales. When scratched lightly with a glass slide, the silver colour of scales becomes more prominent. Further scratching causes pin point bleeding. The common affected sites are the elbows, the knee, the scalp and the sacrum. The lesions vary in shape and size and some lesions may merge to form annular or gyrate figures. Isomorphic lesions of psoriasis may develop at the site of trauma.
In some cases, the nails are also involved showing thimble pitting, yellow discolouration and onycholysis or thickening and ridging of the nail plate.
The disease is chronic with spontaneous remission and relapses at variable intervals. Attacks are more common in winter than summer.
There are many clinical variants of psoriasis:
Guttate Psoriasis
It is characterized by sudden appearance of drop size, erythematous, scaly papules over the trunk and the extremities. It is usually seen in children following a streptococcal upper respiratory infection.
Flexural Psoriasis
Psoriasis in body folds loses its characteristic scales and manifests as itchy, smooth, shiny erythematous lesion.
Pustular Psoriasis
There are two clinical types :
Palmoplantar pustular psoriasis is characterized by presence of erythematous and scaly plaques studded with sterile pustules on palms or soles.
Generalized pustular psoriasis is characterized by an acute eruption of a generalized pustular rash in a psoriatic patient, usually associated with marked constitutional symptoms. It may be precipitated by infections, withdrawal of systemic corticosteriods or irritant applications.
Psoriatic Arthropathy
It is chronic inflammatory arthritis in patients with psoriasis, which chiefly involves the distal interphalangeal joints. It is usually associated with severe psoriasis and nail changes. Sometimes, there is extensive mutilation of the joints of extremities.
Psoriatic Erythroderma
It is characterized by generalized erythema and scaling of the body surface, may occur spontaneously or as a reaction to topical therapy. Some typical lesions of psoriasis can always be detected in this variety.
Seborrhoeic dermatitis, lichen simplex chronicus, lichen planus, diabetes mellitus, gout, malabsorption syndrome and hypocalcemia may be seen in association with psoriasis.
Treatment
The treatment can be considered under the following headings:
General and Non-Specific Measures : These include reassurance, psychotherapy and use of mild tranquillizers to remove the fear of the disease. Eradication of the provocating factors is often helpful. Severe forms of psoriasis require hospitalization and good general nursing care.
Topical Therapy : The topical agents which are most useful, are various forms of tar, salicylic and diathroanol, emollients and corticosteroids.
Liquor picis carb. or crude coal tar (5-10%) in various bases is effective alone or in combination with other adjuvants, such as salicylic acid (3-5%). Coal tar is the basis of widely used Goecherman egimen which consists of local application of crude coal tar to the kin for 24 hours, then after a bath, a ultraviolet therapy is given. This regimen clears widespread psoriasis within 3-4 weeks. Dithranol can be used in concentration of 0.05%, to 0.5% as an alternative to tar. In the standard Ingram technique, the patient is exposed to ultraviolet rays after a tar bath and the lesions are then painted with a paste containing 0.05 to 0.1% diathranol. This regimen also clears most of the psoriasis lesions within 3 weeks. Topical corticosteroid application is indicated in psoriasis of scalp, face, flexures and genilalias. Recalcitrant patches are anatomically unsuitable for occlusion and these may be treated by intralesional injection of steroid.
In acute and unstable forms of psoriasis, bland preparations such as calamine lotion with or without oil, liquid paraffin should be applied.
Systemic Therapy : Systemic medications include methotrexate, corticosteroids and psoralens. Methotrexate is indicated in psoriatic erythroderma, psoriatic arthropathy, generalized pustular psoriasis and intractable and crippling psoriasis. It is given in dosage of 0.2 to 0.4 mg/kg body weight either as a single weekly dose or it can be divided into 3 parts given 12 hourly over 36 hours period. Hepatic, renal and bone marrow functions of the patient should be assessed at a regular interval. Corticosteroids have no place in the management of psoriasis except in severe form of the disease where administration of methotrexate is contra-indicated. Another mode of systemic therapy is by oral psoralen and ultraviolet radiation A (PUVA). 8-methoxypsoralen is given orally in a dose of 0.6 mg/kg body weight, followed 2 hours later by exposure to ultraviolet light.
Other systemic drugs like etretinate, razoxane, hydroxyures and azathioprine are also useful in the treatment of psoriasis.
