Elisabeth G. Richard, MD
Light therapy for skin disease


What is Psoriasis? 

Psoriasis is a common disorder affecting between 1% and 2% of the population that can appear at any age and runs a very unpredictable course. In most patients, the disorder is confined to the skin where it develops as small to large, thickened plaques covered with a fine silvery scale. 

Plaques of psoriasis result from an abnormality of the epidermis which is the most superficial layer on the surface of the skin. In psoriasis, the cells of the epidermis multiply at an abnormally rapid rate so in effect, too much skin is being produced and it becomes thickened and scaly. It is now known that an abnormal immune response causes the skin to react in this way and psoriasis is now considered to be an auto-immune disease. White blood cells enter the skin and release chemicals to cause the skin cells to multiply.

Genetic Factors
- About 70% of patients with psoriasis have a near or distant relative with the disorder. However, the inheritance is somewhat indirect and a child of a patient with psoriasis has only about a 10% risk of developing the disorder at any time in his or her lifetime. 

 - A viral or bacterial infection of the throat can trigger psoriasis but such infections do not tend to make established psoriasis worse.

Psychological Factors - Psoriasis may appear for the first time during a period of stress but more importantly, emotional stress frequently exacerbates psoriasis in a person who already has the disorder. 

 - Abrasion of the skin and blunt trauma can provoke new areas of psoriasis in a person with the disorder. Scratching of the skin has a similar effect. Localization of psoriasis to the knees and elbows is probably due to the repeated knocks received by these parts of our anatomy. 

Pregnancy - Psoriasis frequently goes into remission during pregnancy but also, it often appears for the first time after delivery. 

Finally, we can say that several factors are not important in causing psoriasis. Psoriasis is not an infectious disease and it is not caused by any known bacteria or virus. Diet has no proven influence on psoriasis. Psoriasis is not caused by a vitamin deficiency and is not improved by taking ordinary vitamins. 

Psoriasis and Arthritis 

Approximately 12% of patients with psoriasis have a form of arthritis that is peculiar to this disease and differs from other types of arthritis. The arthritis can precede, accompany or follow appearance of the skin rash, and it predominantly affects the small joints of the fingers and the pelvic joints. Most patients are only mildly affected. 

It must be remembered that other types of arthritis, in particular rheumatoid arthritis, do afflict patients with psoriasis just the same as they afflict patients who do not have psoriasis. Therefore, the appearance of arthritis in a person with psoriasis does not necessarily indicate the two disorders are related. 

Treatment of Psoriasis 

There are many treatments for psoriasis and that is always a certain indication that no one treatment is perfect. All treatments aim to block the rapid multiplication of cells in the epidermis. The amount of treatment, the intensity of treatment, and the type of treatment must be tailored to the individual patient. The most common employed treatments are: 

Topical Treatments 
Various lotions, creams and ointments are used to control mild-to-moderate cases of psoriasis. The advantage of this approach is its convenience since it can be done at home and usually does not involve too much time and effort. The disadvantage of topical therapy is that although it usually produces improvement of psoriasis it does not clear the condition. The most common forms of topical therapy are: 

Tar Preparations 
Lotions, shampoos and creams containing tar have been used for many years. Tar is mildly effective in slowing down the multiplication of cells and is safe to use even if a little messy. 

Corticosteroid Creams 
Hydrocortisone and more potent derivatives, as creams and lotions are effective in improving psoriasis. These preparations are safe and useful in patients with only small areas involved but unfortunately, when used on large areas they are less effective and prone to give rise to adverse effects.

The principal harmful effects are precipitation of extensive psoriasis once they are stopped, atrophy or thinning of the skin (stretch marks) and suppression of the normal function of the adrenal glands; the latter problem can result in shock and collapse if the patient contracts a severe infection or suffers a severe injury. 

Cortisone has also been given as injections and tablets in the treatment of psoriasis. Although this treatment is initially very effective, psoriasis soon becomes resistant and adverse effects are very common. 

Vitamin D Derivatives 
Calcipotriene, marketed as Dovonex, cream and ointment and calcitriol, marketed as Vectical, are additional choices of topical treatments. When used twice daily in a sustained manner they produce considerable improvement in many patients. The main problem with treatment is irritation of the skin that occurs in some patients. If used in excessive amounts there is concern about interfering with calcium balance in the body.

Tazarotene or Tazorac, a gel formulation, is another topical therapy option. This compound is a retinoid or vitamin A derivative and it is moderately effective in treating psoriasis. The main drawback of the treatment is irritation of the skin that occurs in many patients. This problem can be partly relieved by combining its use with corticosteroid cream. 

Ultraviolet Light Treatment 
Most people with psoriasis notice they are better in summer than winter and this is mainly due to the beneficial effect of sunlight. The ultraviolet portion of sunlight is responsible for this improvement. 

The main advantage of ultraviolet or UV treatment is that it converts psoriasis to skin that looks and feels normal and with maintenance treatment, it can be maintained in a normal state. UV treatment, to be effective, usually has to be done in a doctor’s office and therefore it is mainly reserved for patients with moderate to extensive psoriasis. 

The main downside of UV treatment is that it does cause premature aging of the skin and skin cancer but if used carefully in modest amounts it is the safest and most effective treatment for psoriasis.

Several types of UV treatment are available: 

High-intensity Broadband UVB Phototherapy 
Clears many patients in about 30 treatments and can be used as maintenance treatment once or twice a week. 

Narrow-band UVB Phototherapy 
A newer treatment that is more effective and can clear about 80% of selected patients with psoriasis.

PUVA Therapy 
The most effective form of UV therapy clearing over 90% of all patients with psoriasis and maintenance treatment is usually about twice a month. 

Laser Treatment 
The excimer laser which emits ultraviolet light has recently been approved for treating localized small areas of psoriasis. 

Systemic Therapy 
Various medications taken by mouth or injection can be very effective in clearing psoriasis. These are usually reserved for people with moderate-to-severe disease unresponsive to other treatment because they are all associated with significant side effects. 

This is an agent that has been used in the treatment of cancer for several decades and in much smaller doses, it is also effective in the treatment of psoriasis. When used in short courses, as for example in combination with a course of ultraviolet light, methotrexate is a safe and very effective agent and requires only minimum supervision. However, chronic use over long periods can interfere with the function of the liver and close monitoring is required to check for this adverse effect. 

Acitretin or Soriatane 

Acitretin is a derivative of vitamin A that has some effect in the treatment of psoriasis. However, this beneficial effect is mainly confined to people with pustular and erythrodermic psoriasis, and both of these very severe forms of the disorder are fortunately quite rare. The use of retinoids will probably be limited because they produce adverse effects in all patients including changes in the bones and in the lipids in blood. 

Cyclosporine or Neoral 
Also used for the treatment of psoriasis, this is an agent that suppresses the immune system and can be very effective in treating psoriasis. It is usually used for short courses in patients with severe psoriasis since long-term use can affect the function of the kidneys.

Biologic Agents 
Recently, a number of antibody agents which block the inflammation causing psoriasis, have been approved for tratment. these are given by injection into the skin or into veins and can be very effective in treating the disease either alone or in combination with light and other agents. 

The Course of Psoriasis 

Psoriasis is a chronic and unpredictable disorder that may last months or years. There are four important facts to remember: 

  • Psoriasis does undergo spontaneous remission so that 10% of all people who have psoriasis this year will not have it next year. 
  • There is no marker or indicator that will tell us when a particular patient is likely to undergo a remission. 
  • All available treatments are just that, treatment and not cures. None of these treatments influence the natural course of the disorder.
  • New treatments appear at the rate of one or two each year. Effective treatments appear at a rate of one each decade. 

While these facts might at first glance be somewhat discouraging, psoriasis is a treatable condition and should not restrict a fairly normal life provided the therapeutic modalities we have today are correctly used in the individual management of each patient.