Psoriasis and its treatment form a major problem in dermatology. The incidence of the disorder in the general population is calculated to be about 1 to 2 per cent though accurate population studies do not exist. It appears for the first time between the ages of 5 and 25 years in the majority of patients. Once established remissions are uncommon and brief—only about 10 per cent of sufferers being free from all traces of psoriasis for more than 5 years at a time. Girls suffering from psoriasis outnumber boys by 2 to 1 but by the time adult life is reached about 40 per cent of cases are male and there is no difference in the severity of the disease in either sex.
Aetiology. Although the cause is unknown there are several factors which influence its onset, the most important of which is heredity. The incidence of a family history of the disease may vary in different regions depending probably on variations in stability of the population and the resultant differences in inbreeding. In Yorkshire about 33 per cent of psoriatics can trace another similarly affected member of the family. In areas of static population and inbreeding psoriasis may appear in many generations affecting several siblings and in such families the condition tends to be severe and persistent. In a disease which may appear at any age and whose stigmata may be so slight as to pass unnoticed, it is difficult to work out the mode of inheritance, but it appears to be one of irregular dominance in most cases, though sometimes recessive. The risk of psoriasis for children of one affected parent is 25 per cent; for siblings of an affected child with normal parents 17 per cent; for siblings of an affected child with one affected parent 30 per cent.
Another factor which may influence the onset of psoriasis is infection, streptococcal tonsillitis in childhood being the precipitating cause of 50 per cent of acute cases of psoriasis of the widespread guttate pattern in childhood. In patients with the chronic pattern of psoriasis a streptococcal upper respiratory infection may precipitate an exacerbation of the disease. Such an infection is followed by an interval of 10 to 14 days before the onset or flare of the psoriasis suggesting an allergic response to infection as the trigger factor and very rarely one may see another allergic response such as acute nephritis appearing at the same time. Deprivation of sunlight must also play some part in influencing the disease. In sunny climates it is not common in white races and the low incidence in dark skinned races may be partly geographic rather than due to racial differences in incidence. There is however a higher incidence among the races of Northern Europe (the incidence in the Faroe Islands being 2-8 per cent) and a noticeable fluctuation in the disease with the seasons, most psoriatics improving in the summer months. The response of the disease to tropical and subtropic climates depends on its severity. Those with very extensive psoriasis are likely to become worse as the result of sweating and maceration of the skin if exposed to extreme heat and humidity. Those with mild lesions often clear completely in subtropical or tropical countries and remain clear until they return to their native lack of sunshine.
Mental stress is not a common factor in precipitating the first attack of psoriasis, though occasional patients give such a convincingly close history of stress and onset of the disease that it cannot be discounted. It is also supported by the undoubted influence which stress has over the course of established psoriasis, as relapses in extent of the lesions are not uncommon as the result of worry or shock.
The course is also influenced by hormonal factors, commencing or becoming worse with puberty or at the menopause and often improving during pregnancy. Whether the condition has altered during pregnancy or not it usually relapses after childbirth. Despite these influences there is no evidence that psoriasis is caused by hormonal factors. In recent years it has been recognised that drugs may not only provoke a nonspecific eruption on top of which psoriasis may appear as a Koebner phenomenon, but also that some drugs aggravate psoriasis, the recognised ones being chloroquine, chlorpropamide and practalol.
Clinical features. The lesions of psoriasis consist of sharply demarcated red or pink areas of skin with silvery scaling which may become heaped up on the affected areas. If scaling is not obvious the characteristic silvery colour of the scales appears when the lesion is scratched, scratching causing separation of surface scales and allowing air between them to reflect back the light. Further scratching separates the scaly layer from a velvety red epidermis in which bleeding points appear where the tips of the papillae and the capillaries have been damaged.
The pattern, distribution and extent of these lesions varies greatly. In an acute attack of psoriasis, which is commoner in childhood and often precipitated by infection, the lesions are tiny discs, described as guttate, scattered evenly over the body and limbs, usually also in the scalp and sometimes on the face. Unlike pityriasis rosea, the lesions are round rather than oval and do not show the patterning of the lines of cleavage of the skin. When it appears in childhood this acute attack usually clears spontaneously in 2 or 3 months but most of these children will later develop a chronic pattern of psoriasis and in half of them this will appear within 5 years. Infection may similarly produce a guttate attack of lesions in adults who have established chronic psoriasis.
Chronic lesions classically appear as plaques on the knees and elbows, a solitary lesion of this type may pass unrecognised or even unnoticed for years. Other characteristic areas are over the sacrum and in the scalp. The scalp lesions remain as sharply demarcated as those on the rest of the skin and as the scales tend to be anchored by hair they may accumulate considerably so that the lesions can be located by touch. They differ from seborrhoeic dermatitis in that this produces a diffuse scaly erythema extending to the hair margin without much heaping of scales. In most patients hair growth is not affected but in a few hair may be severely thinned in density in the affected areas of the scalp.
Other plaques of varying size and pattern may appear anywhere on the trunk and limbs, often producing remarkably symmetrical lesions in a mirror image pattern; sometimes large sheets, sometimes discs or annular lesions which revert to normal skin in the centres.
In some case these sheets may spread rapidly , often as the result of maltreatment, until they coalesce to cover every inch of the body producing a picture indistinguishable from exfoliative dermatitis. The history of the state of the skin before generalisation of the eruption differentiates the conditions; clinically there is less oedema of the skin in exfoliative psoriasis and reactive lymph node enlargement is not a feature.
Involvement of the finger nails occurs in about a quarter of all cases and is sometimes seen as the only manifestation of psoriasis. Pitting resembling that on a thimble is the commonest change, but either in association with this or alone, the nails may be ridged transversely and scales heap up under the ends of the nails, producing thickened opaque and discoloured nails which, with severe involvement, become broken or loose and severely malformed.
Lesions may appear in the axillae, groins and umbilicus which, because of the moist situation, do not become scaly and may even exude serum. In these areas psoriasis maintains it sharply demarcated edge which differentiates it from seborrhoeic dermatitis or moniliasis.
Flexural lesions can occur at any age but are a special feature of psoriasis in middle aged women at or beyond the menopause; a careful search for other manifestations of psoriasis usually reveals the true nature of the lesion.
Alteration of the usual appearances of the lesions on the palms and soles can lead to difficulties in diagnosis. Small scaly discs may be scattered over the palms, these usually also affect the knuckles and give rise to much discomfort by their tendency to fissure. Sometimes these hyperkeratotic discs may coalesce to form one large hyperkeratotic area over the palms or soles which is usually itchy. In addition to redness and scaling, pustules may appear on palms and soles situated deep in the epidermis; because of the toughness of the horny layer these do not rupture, but resolve leaving yellow thickenings of the epidermis which eventually are desquamated. In the absence of other lesions of psoriasis, pustular lesions are difficult to differentiate from the pustular lesions found in recurrent pomphloyx of the palms and soles or some cases of eczema of palms and soles, chronicity and resistance to treatment being more of a feature in pustular psoriasis.
Arthropathy. Psoriasis is sufficiently common for it to appear in conjunction with rheumatoid arthritis and osteoarthritis in many cases. There is however a type of psoriatic arthropathy which seems to be a separate entity.
The incidence in sufferers from psoriasis is low and although about 7 per cent occur amongst hospital patients the onset of arthritis makes hospital attendance more likely. Any joints may be affected but the most typical are the interphalangeal joints and the lumbar spine. The terminal interphalangeal joints are usually involved as opposed to the proximal interphalangeal joints in rheumatoid arthritis and almost invariably the affected fingers show nail changes. X-rays show erosive changes in the affected areas and the Rose Waaler test, which is positive in 80 per cent of cases of rheumatoid arthritis, is negative in psoriatic arthropathy. It is not common for this type of arthritis to progress to severe deformity, though very rarely absorbtion of the phalanges may produce ‘concertina-like’ changes in the fingers.
Pathogenesis. The histological changes are those which one would expect in a lesion which daily produces quantities of scale; the horny layer is increased and the cells retain degenerate nuclei instead of forming amorphous keratin. The whole epidermis is thickened in the lesions and there is increased mitotic activity. In radioisotope studies it has been shown that the time for epidermal replacement in the plaque is 3 or 4 days as compared with about 28 days for normal skin. In the dermis there is a cellular infiltrate and a characteristic feature is the dilatation of capillaries high in the dermis which on capillary microscopy have a tortuosity which has been likened to glomeruli.
Associated with the increased cellular activity in the plaques there are metabolic and enzymic changes, but these can also be demonstrated to a lesser degree in the normal skin of the psoriatic subject and the capillary changes can also be observed in the psoriatic’s clinically unaffected skin.
It is concluded that the failure of maturation of the epidermal cells and the resultant abnormal keratinisation induces hyperplasia of the epidermis. The cells become more active, the cell cycle is altered and the enzymatic changes are probably a result rather than the cause of this changed metabolism.
Course. The course of psoriasis is so variable, the disfigurement it produces so distressing and its response to psychogenic factors so marked that it lends itself to quack therapies whose worth is disproportionate to their expense. For this reason medical practitioners should maintain an optimistic approach to treatment as although permanent cure is not possible, very much can be done to ameliorate the condition.
Patients looking back on a lifetime of psoriasis can often recall periods of months or years when the disease was extensive and distressing. Puberty, the late teens and early twenties and the menopause are the ages of stress when psoriasis, in common with many other skin complaints, may flare up, but often there are long intervals between when a few patches on knees and elbows are the only trace.
Treatment. Acute guttate psoriasis subsides spontaneously and sometimes completely in 2 to 3 months. At the stage of eruption it is easily irritated by local applications or ultraviolet light and treatment should be confined to a simple bland application such as 4 per cent liquor picis carb. in aqueous ointment B.P. for a few weeks until the lesions become static, after which it can be treated in the same way as chronic psoriasis.
Many patients with chronic psoriasis respond quite dramatically to local applications only. They should be instructed to soak at night in a warm bath and scrub the scales off the lesions with a soft nail brush. After drying the skin coal tar and salicylic acid ointment B.P.C. is rubbed into the lesions and they are then covered with stockinette or ‘Tubegauze’ to keep the ointment off the clothes. If tar applications do not help, dithranol may be applied in a base of equal parts of hard and soft paraffin. A start should be made with 1/4 per cent dithranol but if the surrounding skin is not irritated the concentration can be increased gradually to 5 per cent if necessary. Dithranol stains the skin round the lesions black; as desquamation in the lesion ceases this too takes up the stain as an indication that resolution has occurred. Dithranol should not be used in the flexures as there is a risk of folliculitis, or on the face where the more sensitive skin is easily irritated, in these areas triamcinolone or fluocetonide ointments penetrate the skin sufficiently well to control most cases.
Psoriasis of the scalp is more difficult to control and requires conscientious application. The scalp should be washed in 1—2 per cent Cetrimide (Cetavlon) nightly or as often as possible, after which in mild cases a 2—4 per cent liquor picis carb. in a cream base applied to the scalp. In cases where scaling is more severe the messy application of Ung. pryogallol co. or dithranol pomade after washing are the only really effective treatments. The hair should be parted in turn from one side of the scalp to the other and the ointment applied to the scalp so that the hair is not matted down.
If local applications do not help the most useful adjunct is ultraviolet light therapy. Suberythema doses 3 times weekly are of considerable value and local treatment with ointment is continued while this is given. The skin pigments in about 6 weeks and after this there is little further improvement. A modification of the Goeckerman regime using the light sensitising effect of tar gives very much better results: the patient soaks for 10 minutes in a warm bath to which liquor picis carbonis has been added (120 ml in 90 litres of water) or ‘Polytar emollient’. Scaly lesions are scrubbed with a soft nail brush. After drying the patient is exposed to ultraviolet light for a subervthema dose, the time of exposure being increased by 30 seconds each day. The lesions are then anointed with coal tar and salicylic acid ointment and the limbs and the trunk covered with stockinette. This process takes half-an-hour each day and the patient can then return to work. Mild cases may clear after 3 weeks of this treatment but severe cases require up to 6 weeks. About a third of patients clear completely and all except about 10 per cent derive great benefit, lesions remaining being minimal. In patients with very extensive psoriasis treatment by the same method in hospital may be preferable and then it is rare for it not to clear completely, sometimes in two to three weeks.
Systemic therapies which are known to affect the eruption all have the disadvantage of toxicity. The only corticosteroid which has any definite effect on psoriasis when given by mouth is triamcinolone but any suppressive effect it may have soon diminishes and psoriasis reappears if the drug is continued or relapses with redoubled spread if the drug is stopped. Systemic corticosteroids should not be used in the treatment of uncomplicated psoriasis. Because of the increased mitotic activity in the lesions antimitotic drugs have been used in treatment for 20 years and the Srug commonly prescribed is the folic acid antagonist methotrexate. This is usually given orally and there are advocates of various regimes, one routine being 10 to 15 mg given in divided doses over 24 hours once each week. Methotrexate is undoubtedly effective but its toxic effects severely limit its use. It should not be given in the reproductive period of life for fear of teratogenic effects. It may depress bone marrow activity to a dangerous degree and thus frequent routine blood counts are necessary. In a few patients even a small dose can suppress activity in the lesions to such an extent that they necrose and leave large raw areas. Finally, the drug has been shown to concentrate in the liver and if combined with a high alcohol intake cirrhosis is probable. A liver biopsy before starting treatment and at increasingly long intervals of a year or two while on the drug is desirable. Obviously the patient must also be warned to avoid alcohol. It is therefore a drug to be used only for incapacitating psoriasis and under close hospital supervision.
Hydrocortisone applied to the skin has no effect on psoriasis but the more powerful fluorinated steroid ointments suppress psoriasis of the flexures and face. Applied at night under a sheet of polythene to make the psoriatic area airtight, chronic lesions on limbs and trunk resolve in about a week. This treatment has no effect on psoriasis in the acute or eruptive stage, and when application stops the lesions often recur within a week or two, maintenance therapy without occlusion usually being necessary. Folliculitis under the polythene is a complicating side effect but is less common if the lesions are occluded only at night rather than for longer periods. Expense and rapidity of relapse, sometimes with rebound spread of lesions make the treatment of doubtful value in extensive psoriasis but it is useful for chronic localised lesions and in pustular psoriasis of the palms and soles which usually resist other treatments.
Psoriasis of the nail plates is difficult to help, but if it is severe enough to warrant treatment infiltration of the nail bed with triamcinolone is effective. The pain of the injection can be diminished with local anaesthetic.
Once psoriasis is clear the question of preventing recurrence arises. In acute psoriasis following tonsillitis, especially if this has recurred more than once, tonsillectomy may be considered, but the tonsils should only be removed on their own merit, as the influence on the future course of psoriasis is doubtful.
After ultra-violet light therapy the period of freedom from lesions varies from a few weeks to years, but in most patients fresh lesions appear in an average of 6 months. The use of an ultra-violet lamp at home as a prophylactic measure may lengthen the remission but will do little to influence the relapse when it does occur.