Psoriasis is an autoimmune disease characterized by abnormal patches of skin.Psoriasis can start at almost any age and involves both the sexes equally. It manifests in a variety of forms.
The most frequent manifestation is called plaque type psoriasis where the lesions characteristically consist of well demarcated erythematous plaques covered with loosely adherent silvery scales, the silvery colour of the scales becoming more prominent when attempts are made to scrape them off.
The lesions vary in shape and size and with peripheral extension some lesions may coalesce to form large gyrate or geographical patterns. Extensor aspects of the extremities, particularly the elbows and the knees, the sacral region of the back and the scalp are the usual sites. Scalp involvement is rare in children.
The disease undergoes spontaneous remissions and relapses at variable intervals, but most patients are worse during winter.The lesions may become very extensive and change to exfoliative dermatitis.
Some patients also have involvement of the joints in a manner which resembles that of rheumatoid arthritis.
In some cases one or more of the nails are also involved showing one of the following
- Occurrence of multiple pin-point sized pits on the surface of the nail plate
- Onycholysis-Separation of the nail plate from the nail bed which shows as an area of yellowish discolouration
- Onychodystrophy- Thickening, brownish discoloration and irregularity of the nail plate.
Pustular psoriasis is another variant in which the lesions are mostly superficial pustules.
These pustules may be located over the psoriasiform plaques or even on normal skin, and contain large numbers of polymorphs. Bacteriologically however, such pustules are sterile. The lesions may be limited to the palms and/or soles only with or without fever and toxaemia, or the pustules may appear all over the body when the disease is potentially more serious and requires urgent treatment.
The aetiology of psoriasis is not known. In 10-30 percent cases it is found in more than one member of the family. The main defect seems to be in the mechanism which controls the rate of epidermal cell division.
Normally, the epidermal cells divide at a fixed controlled rate. At this rate a newly formed cell at the basal layer takes nearly one month to transform into and get shed off from the skin surface as a keratinized cell. In psoriasis lesions this rate is increased almost ten fold. This leads to formation of immature epidermal cells which are shed as scales.
Trauma often triggers the formation of psoriasis lesions and this is the probable reason why psoriasis lesions are frequently located on the extensors of the elbows and knees. Sometimes, the lesions are situated in a row as if occurring along the line of a scratch (Koebner phenomenon). The reason why psoriasis is usually worse during winter is also not known, but sunlight has a very beneficial effect on psoriasis.
That may possibly be the reason why psoriasis is almost never seen on the face and generally remains confined to the covered parts of the body. Certain drugs such as chloroquine, idomethacin and lithium are known to cause aggravations of psoriasis, while corticosteroids are likely to precipitate pustular psoriasis when the corticosteroids are withdrawn.
Pustules in pustular psoriasis are believed to be caused by the deposition of stratum corneum antibodies, activation of the complement and release of chemotactic factors. Guttate psoriasis is probably an immune complex disease though a streptococcal proliferative factor has been shown to cause proliferation of the keratinocytes as well.
Diagnosis of Psoriasis
The diagnosis in psoriasis can be confirmed by the grattage test or by taking a skin biopsy.
Gentle scraping of the surface of a psoriasis plaque with a glass slide will remove the loosely attached scales and reveal a shiny surface peppered with fine bleeding points. These bleeding points represent the dilated and tortuous capillary blood vessels in the papillary dermis, one of the characteristic pathological events taking place in psoriasis affected skin. This sign is known as Auspitz sign, which is a diagnostic sign of psoriasis
Treatment of Psoriasis
Cases having plaque type of psoriasis should be managed with local treatment alone. An ointment containing three percent salicylic acid one percent ammoniated mercury, six percent liquor picis carbonis and 12 percent icthyol petrolatum, massaged into the lesions once at night, usually leads to regression of the lesions within one or two weeks.
Salicylic acid acts as a keratolytic agent and helps to remove the scales; ammoniated mercury helps in proper keratinisation, liquor picis carbonis acts as a keratoplastic; icthyol acts as in anti-inflammatory agent and petrolatum acts as an emollient. In case any of the ingredients is not available, it can be omitted, and the patient treated with the remaining ointment. Even plain petrolatum is often able to produce regression of the lesions. Crude coal tar alone can also be used in a concentration of six percent in petrolatum.
Dithranol is another agent which can be used for psoriasis. A commercial ointment containing 1.15 percent dithranol which also contains 1.5 percent salicylic acid and 5.3 percent coal tar applied on the lesions once a day lead to disappearance of the lesions in 2-3 weeks. Some patients however develop intense redness of the skin which indicates that the quantity of the medicine applied should be reduced.
Dithranol is also likely to stain the clothes. Recently, some workers have developed a new method in which the dithranol ointment is applied only for 10-30 minutes and then removed with mineral oil. This regime is called minutes therapy and is quite effective in plaque type of psoriasis. A preparation containing dithranol is combination with corticosteroids is also available, and irritant reactions with this combination are far less frequent.
Topical corticosteroid ointments with or without salicylic acid have also been found to be very effective in treating plaque type of psoriasis. Generally, two applications a day with good massage are adequate to clear up the lesions in about two weeks, but for palmar or plantar lesions, or if the scales are too thick, even more frequent applications may be made.
Scalp lesions also can be treated with any of the above mentioned ointments and the patient should be encouraged to shampoo the hair daily or at least as frequent as possible.
Nail lesions are more difficult to treat with topical medicines because the medicines cannot reach the nail matrix so easily. Minor defects like pitting of the nails may not be treated at all. For onycholysis, however, the ointment must be applied under the nail plate, on the involved area. This part of the nail should be clipped as close as possible.
For severe involvement of the nail like onychodystrophy, the ointment should be applied at the posterior nail fold because that is the area under where the nail plate is being formed, but the effect of the topically applied medicines is limited because the nail matrix is situated quite deep and the superficially applied ointments may not reach the areas unless massaged several times a day.
To achieve better results, corticosteroids may be injected under the posterior nail fold but the needle injections are too painful in this area and dermojet injections are only slightly less painful. In case nail involvement is associated with severe psoriasis on the skin, systemic treatment for the rest of psoriasis will automatically look-after the nail changes as well.
Systemic treatment should be undertaken whenever a patient cannot be managed with local treatment alone. This is especially necessary if the disease is extensive, new lesions continue to appear or the old lesions continue to extend. Patients having guttate psoriasis, exfoliative dermatitis, or generalized variety of pustular psoriasis, as a rule require systemic treatment.
Corticosteroids given systemically in an adequate dose can bring about an effective control of the disease, but it has frequently been observed that some psoriasis patients treated with systemic corticosteroids tend to have more severe relapses or develop pustular psoriasis when the corticosteroids are eventually withdrawn.
Corticosteroids should therefore, be avoided as far as possible for the treatment of psoriasis. Methotrexate is generally useful for extensive plaque type psoriasis, psoriasis erythroderma, pustular psoriasis and psoriasis with arthropathy. It can be given either in a single dose of six to nine tablets (2.5 mg each) or in three 12-hourly doses, once a week, and most of the cases would be under control within a few weeks.
Methotrexate can then be gradually withdrawn at the rate of one or two tablets per month taking the clinical condition of the patient as the guideline. A small dose may be continued for several months as a maintenance if the patient tends to relapse on withdrawing the dose completely. The main drawback of treatment with methotrexate is its toxicity.
It should not be given to pregnant ladies or children, and a strict check should be maintained on SGOT and SGPT levels and total leucocyte counts at least once a month. In case there is any rise in the levels of these liver enzymes or a decrease in the TLC below 4000 cell, treatment with methotrexate should be suspended till the values return to normal. Some authorities recommend liver biopsies at 6-12 month intervals to keep a control on the development of cirrhosis and stop at a total dose of 2 gm. Other cytotoxic drug are less effective.
An alternative method consists of giving oral psoralens in a dose of 10 to 30 mg a day followed two to four hours later by exposure to long wave ultraviolet UVA light (320-400 nm) in the same manner as for vitiligo. This treatment is called PUVA. Since this therapy requires daily visits to the clinic, it can be given to only a few selected cases who do not respond to the routine treatment.
Use of sunlight instead of long wave ultraviolet light has also been recommended and is called PUVASOL. The duration of exposure can in the beginning be five minutes, to be raised later to 30 minutes depending upon the patient’s tolerance. In severe cases who are resistant to other measures, repeated haemodialysis or peritoneal dialysis have also been observed to result in remissions. The mode of action of these procedures is not understood.
For localized patches of psoriasis or if the lesions are resistant to local therapy, intralesional corticosteroids or occlusive dressing with corticosteroid ointments are very useful.
Patients having guttate psoriasis usually respond to one or two courses of systemic antibiotics. One can start with any antibiotic and if there is no response within a week’s time, it is better to try another antibiotic during the next week. The antibiotic should be continued till the guttate lesions have regressed completely. The response to antibiotics however is not uniform in all cases, and some patients respond to even ketoconazole given in an oral dose of 200 mg a day.