Psoriasis is a chronic disorder involving excessive production of skin cells. It affects more than 5 million Americans and nearly 80 million people worldwide.
Normally, skin cells are lost and replaced within about 27 days. In patients with psoriasis, the life cycle lasts only four days. As a result, patients may have abnormal thick, patchy skin. The cause of psoriasis is multifactorial, involving genetics, inflammation, and immune dysfunction.

Plaque psoriasis (also known as psoriasis vulgaris) is the most common form, accounting for 80 percent of cases. It is marked by symmetrically distributed skin patches and scales that occur primarily on the elbows, knees, scalp, and lower back, and may be painful or disfiguring. In addition, nail changes, including discoloration and thickening, occur in 50 to 80 percent of cases.

In most cases, the symptoms come and go over time and may be related to medications, trauma, stress, alcohol, or tobacco use. In severe cases, lesions cover more than 10 percent of the body and can have a significant effect on self-esteem and quality of life, sometimes contributing to depression and suicidal thoughts. More severe symptoms, including psoriatic arthritis, occur in 10 to 25 percent of patients, sometimes resulting in permanent joint damage if left untreated.

Risk Factors

Psoriasis can occur at any age, although most cases begin between the ages of 20 and 40. All races are affected, but the disorder is less common in African-Americans. Other factors associated with risk follow:

• Genetics: There is a clear genetic predisposition. Nearly half of psoriasis patients have an affected first-degree relative.
• Medication: Medications known to exacerbate symptoms include lithium, malaria antibiotics, beta-blockers, ACE inhibitors, and nonsteroidal anti-inflammatory drugs (e.g., ibuprofen).
• Steroid therapy withdrawal: Abrupt ending of steroid therapy (e.g., prednisone) can result in the sudden worsening of psoriasis.
• Infection: People with HIV and children with recurring infections, particularly streptococcal pharyngitis ("strep throat"), are at increased risk.
• Stress: Emotional and physiologic stress (trauma) has been linked to exacerbations, which may occur up to a month after the stressful event.
• Obesity: See Nutritional Considerations.
• Climate: Moderate amounts of sunlight can improve psoriasis. However, excessive sun exposure can trigger or exacerbate the disease.
• Alcohol intake and tobacco use are also important risk factors.

Psoriasis: Diagnosis and Treatment

Diagnosis

• A medical history and physical examination are the first steps. Psoriasis is usually diagnosed by the appearance and location of skin plaques.
• Blood tests are not available to confirm or exclude the diagnosis.
• In some cases, a skin biopsy may be helpful to identify the diagnosis.
• Psoriatic arthritis, which primarily affects the joints of the hand, is diagnosed by history, physical examination, and exclusion of other arthritic disorders, such as rheumatoid arthritis and gout.

Treatment

Despite a wide range of therapeutic options, psoriasis can be a challenge to treat. Treatments are based on the type of psoriasis, severity, and areas of skin affected.

• Topical creams and ointments are the initial therapy for mild to moderate disease. Topical corticosteroids are especially useful for advanced disease.
  
  Coal tar is probably the oldest known treatment and is used to reduce inflammation, itching, and scaling. Moisturizing creams and ointments can also reduce itching and scaling. However, lotions have the reverse effect. Medicated shampoos are used for scalp lesions.
• Phototherapy is known to be beneficial and is used especially for widespread disease. Options include natural sunlight (lesions usually improve during the summer) or ultraviolet radiation. Phototherapy may be combined with topical treatments to increase efficacy.
• In severe disease, oral medications may be necessary. Options include oral retinoids (e.g., acitretin), methotrexate with folic acid, azathioprine, cyclosporine, sulfasalazine, and hydroxyurea. These can have significant side effects and cannot be used in pregnant women.
• Psychological approaches may be valuable in individuals with psoriasis. Stress plays an important role in the onset, exacerbation, and prolongation of the disease, and may decrease the effectiveness of treatment. Some evidence indicates that hypnosis and cognitive-behavioral therapy reduce symptom severity.

 Psoriasis: Nutritional Considerations

• Fasting, low-calorie diets, and vegetarian diets have all been shown to reduce the symptoms of psoriasis.
  
  Part of the effectiveness is likely explained by weight loss. Obesity is significantly more common in patients with psoriasis than in control subjects. Recent evidence indicates that severely overweight individuals have nearly twice the risk of developing psoriasis.
  
  These dietary adjustments may also be beneficial by decreasing inflammation.
• Essential fatty acids: Patients with psoriasis may demonstrate a deficiency of omega-3 fatty acids, which act to decrease inflammation, and elevations of omega-6 fatty acids, which increase inflammation.
  
  Some studies have found that supplementation with omega-3 fatty acids improves the effectiveness of psoriasis treatment. Although long-term controlled trials are necessary to determine whether supplementation with omega-3 or omega-6 fatty acids is a useful treatment, patients would do well to increase dietary intake of healthful foods with omega-3 fats, such as walnuts, flax seeds, or flax seed oil, and decrease intake of foods with high concentrations of omega-6 fats, such as meat, eggs, and milk.
• Alcohol avoidance: Excess alcohol intake is an important risk factor for psoriasis. In alcohol abusers, the disease often remits when they quit drinking and recurs upon resumed alcohol use. Even in light to moderate alcohol users, alcohol consumption is correlated with worsening symptoms.