Psoriasis is a chronic skin disease, which causes sharply defined red patches covered by a silvery, flaky surface. Psoriasis tends to get better and worse at different times of your life. These periods of activity and remission are often impossible to predict. Psoriasis may be limited to a few areas of the skin (mild) or it may be widespread (moderate to severe).

A normal skin matures in 28-30 days and sheds from the skin unnoticed. Psoriatic skin cells mature in only 3-4 days. These skin cells build up on the surface of the skin and form silver scaly lesions. Often these scaly lesions cause no symptoms but they can be painful and itchy, and they can crack and bleed.

Psoriasis occurs throughout the world. Men and women appear to be at equal risk but the disease often develops later in men. About 40% of patients report developing psoriasis before age 20 and 10% had the disease before age 10. It is less common in some races with pigmented skins.
Psoriasis is not contagious; you cannot pick it up from someone else or they cannot pick it up from you 

Causes

The precise causes of psoriasis are unknown, though genetic and environmental factors as well as an excessive inflammatory response may play a part.

• Genetic Factors: About 35% of those with psoriasis have one or more family members with the disorder. Your risk of developing psoriasis at any time in your life is 4% in someone with no affected family members, 28% with one affected parent, and 68% if both parents are affected by psoriasis.
• Inflammatory Response: The immune system seems to play a role in damaging the skin cells.
• Environmental Factors:

1. Weather: Cold dry weather is a common precipitant of psoriasis flares. Hot, damp, sunny weather helps relieve the problem in most patients. However, some people have photosensitive psoriasis, which actually improves in winter and worsens in summer when exposed to sun.
2. Emotional trauma: Stress, anger or anxiety can trigger psoriasis; e.g. a child followed through adolescence may have a flare-up of the disease with the stress of school examinations.
3. Infections: Infections caused by viruses or bacteria can trigger some forms of psoriasis. Streptococcal infections in the upper respiratory tract, such as tonsillitis, sinusitis, and so-called "strep" throat, are known to trigger psoriasis, particularly guttate psoriasis in children. The human immunodeficiency virus (HIV) is also associated with worsening of psoriasis.
4. Mechanical trauma and Koebner response: Repeated trauma to the skin over elbows and knees as a part of every day activity may explain the common involvement of these sites with psoriasis. The Koebner response is a phenomenon in which psoriasis develops in regions of the skin that are the sites of previous injuries, such as cuts, burns, or injections. Therefore psoriasis will often affect old operation scars. Drugs that cause rashes can also trigger psoriasis as part of the Koebner response, i.e. a drug causes a rash and then the psoriasis affects this rash because of the Koebner response.

•  Drugs: A number of drugs can worsen psoriasis, including the anti-malarial drug chloroquine, beta-blockers and angiotensin-converting enzyme (ACE) inhibitors (drugs used for hypertension and heart problems), progesterone, and lithium (used in certain forms of depression). Lithium may actually trigger the onset of the disease as well as cause severe flares in people who already have it. Indomethacin, a non-steroidal anti-inflammatory (NSAID) drug, can cause or worsen psoriasis.

Withdrawing from oral steroids or high-potency (very strong) steroid ointments can cause flare-ups of severe psoriasis, including guttate, pustular, and erythrodermic psoriasis. Because these drugs are also used to treat psoriasis, this rebound effect is of particular concern.

Types of Psoriasis

A number of different forms of psoriasis occur.

Plaque psoriasis:
The most common form is plaque psoriasis. Lesions are well demarcated (i.e. they have a clearly defined edge); the base is salmon pink in colour and the tops of the lesions are covered by silvery scaling. The patches start off in small areas, about one-eighth of an inch in diameter, but gradually enlarge and develop into a plaque (a larger raised area with a flat top).

If the plaque is scratched or scraped, bleeding spots the size of pinheads appears underneath (known as the Auspitz sign). Patches usually appear symmetrically, that is, in the same areas on opposite sides of the body. They most often occur on the scalp, elbows, knees, and the lower back. At the onset of the disease, the patches are separate, but they may join together to form larger areas as the disorder develops. In some cases the patches can become very large and cover wide areas of the back or chest.

Patches may persist for long periods, but more often they flare-up periodically, triggered by certain factors, such as cold weather, infection or stress and improve then later. Patches on the trunk improve faster, than those on the arms, which improve faster than those on the legs

Flexural/Inverse psoriasis:

This is a less common type that may be seen together with plaques or may occur alone. Lesions have pinkish glazed appearance, and are clearly defined and non-scaly. They most often occur under the breasts, under the arms or in the groin area.

Guttate psoriasis:

Guttate psoriasis consists of “teardrop patches”, that is numerous small patches of psoriasis (with the typical pink base and silvery scales). These usually erupt suddenly on the trunk, arms, legs, or scalp. This condition usually affects children and young adults, often about one to three weeks after a viral or bacterial (usually streptococcal) infection in the lungs or throat. It may be the first manifestation of psoriasis, but it can also develop in people who have had the condition for some time, particularly in those treated with widespread topical corticosteroid dressings. The teardrop patches often resolve on their own, with out any treatment.

Seborrheic psoriasis:

Seborrheic psoriasis appears as red scaly areas in the scalp, behind the ears, above the shoulder blade, in the armpits, the groin and in the centre of the face.

Nail psoriasis:

Over half of patients with psoriasis have abnormal changes in their nails. The characteristic signs are tiny white pits scattered in groups across the nail. Long ridges may also develop across and down the nail. Toenails, and sometimes fingernails, may have yellowish spots.

The nail bed often separates from the skin of the finger and collections of dead skin can accumulate underneath the nail. Such nail changes may appear before psoriatic skin eruptions occur and, in some cases, may be the only sign of psoriasis. When only one or two toenails are affected it may be difficult to distinguish from a fungal infection.

Generalised or exfoliative erythrodermic psoriasis:

In rare severe cases, psoriasis develops into generalised erythrodermic psoriasis (also called psoriatic exfoliative erythroderma), in which the disease covers all or nearly all of the body, with the entire skin surface becoming scaly and red. About 20% of such cases evolve from psoriasis itself. It can also be caused, however, by certain psoriasis treatments, including withdrawal from corticosteroids, synthetic antimalarial drugs, and potent ointments. This is very serious and needs immediate treatment.

Pustular psoriasis:

In some cases, the psoriasis patches become pus-filled and blister-like eruptions a condition known as pustular psoriasis. It may evolve from plaque psoriasis or erupt at the onset in pustular form. The blisters eventually turn brown and form a scaly crust or peel off. An infection, pregnancy, or certain drugs may trigger pustular psoriasis. It can also accompany other forms of psoriasis.

Pustules usually appear on the hands and feet; when they form on the palms and soles, the condition is called palmar-plantar pustulosis. In rare cases, pustular psoriasis combines with generalised erythrodermic psoriasis and becomes widespread, a dangerous variant called Von Zumbusch psoriasis. Fortunately, this is very rare.

Psoriatic arthritis:

Psoriatic arthritis is an inflammatory condition that is associated with psoriasis, but is considered a unique disorder. It affects between 7% and 42% of psoriasis patients, generally those with severe psoriasis or those who have AIDS, and is characterized by stiff, tender and inflamed joints. Arthritic and skin flare-ups tend to occur at the same time. Psoriatic arthritis usually affects less than five joints, often in the fingers and toes, but it can also occur in the knees, hips, and elbows. About 40% of these patients have arthritis in the spine (spondylarthropathy). About 80% have psoriasis in the nails.

Expected Duration

Psoriasis is a chronic disorder with remissions and recurrences.

Prevention

There is no prevention.

Treatment

Although the treatments available will improve your psoriasis, none will cure it forever. Your psoriasis is likely to recur, particularly if you do not look after it.
Treatment for psoriasis varies depending on the type of psoriasis, the amount and location of affected skin, and risks and benefits of each treatment.
Topical treatments - These are treatments applied directly to the skin. You will need to work with your GP to find which treatment suits you best. No one treatment is ideal or suits everybody. They include:

1. Emollients (for lubrication, such as petroleum jelly). Everybody with psoriasis will need to use emollients. These will help to remove the scales so that any other cream can penetrate to the base of the patch
2. Salicylic acid helps to remove scale particularly if they are thick. It is usually mixed with other ingredients such as Coal tar
3. Coal tar based ointments, while these can be very effective a lot of patients find them very messy to use.
4. Dithranol, which can be applied as either a solution or cream, is usually applied and left for about 30 mins before it is washed off. At low doses it can be used at home but if you need the concentrated solutions applied, you may need to be admitted to hospital. It stains normal skin (although this will fade) and clothing
5. Tazarotene, a derivative of Vitamin A, is applied to the skin, but it is irritating to normal skin and is extremely dangerous during pregnancy and must be avoided by all women of childbearing years
6. Corticosteroid creams and ointments, available in high-potency forms for stubborn plaques on the hands or feet and in milder forms for areas of delicate skin, such as the face. There is a danger of a rebound worsening of psoriasis on stopping the corticosteroid creams
7. Calcipotriol - a synthetic form of vitamin D, which slows production of skin

In general, topical treatments are the first line for mild to moderate psoriasis, but they may also be used alone or in combination with more powerful treatments for more severe cases.

Occlusive tapes:

Watertight (occlusive) tapes may help heal psoriasis and are particularly useful for psoriatic cuts on the palms and soles. Occlusive tapes retain sweat, which helps restore moisture to the outer skin layer and prevent scaling. They should only be used on your doctor's advice, particularly if you are using some of the creams mentioned above.

Phototherapy - For extensive or widespread psoriasis, "light treatment" (using ultraviolet B, or UV-B light, similar to what is used in a tanning booth) may be used alone or combined with tar. In psoralen ultraviolet light treatment (PUVA), an ultraviolet light is combined with an oral medication (called psoralen, which improves the effectiveness of the light treatment). You should not use sun beds or tanning lamps to treat psoriasis. Ultraviolet light may increase your risk of developing a skin cancer

Systemic treatments- Systemic treatments involve oral or injected drugs, which affect the entire body. Many of the systemic drugs used for psoriasis are also used for other severe diseases, including autoimmune diseases (especially rheumatoid arthritis) and cancer.

Nearly all are powerful medications with potentially serious side effects involving the liver, kidney or blood; therefore, understanding the risks and close monitoring of their effects is essential. These drugs should be used only for severe incapacitating cases of psoriasis that do not respond to lifestyle changes or topical or less potent therapies. Patients are usually prescribed these drugs under Specialist supervision.

Some treatments include;

1. Methotrexate. This drug is also used for the treatment of Rheumatoid arthritis and cancer. It is an effective treatment for psoriasis and is often used to treat psoriatic arthritis. You will need regular blood tests to check your blood count and to check that the Methotrexate is not damaging your liver. Methotrexate may be dangerous for unborn babies and therefore should only be used in women of childbearing age, if they are using adequate contraception.
2. Cyclosporin. This drug influences the body's immune response. It can also damage your kidneys and you will need regular blood tests to check this.
   Other drugs that are sometimes used include hydroxyurea, sulfasalazine and thioguanine.

Prognosis

For most patients, psoriasis is a long-term condition. Although there is no cure, there are many effective treatments. In some patients, Doctors or Specialists routinely switch treatments every 12 to 24 months to prevent them from losing their effectiveness and to decrease the risk of side effects.