Psoriasis

Psoriasis is a chronic, noncontagious autoimmune disease. It is characterized by patches of abnormal skin that appear red, pink, or purple. These areas are often dry, itchy, and scaly.

The disease affects between 2% and 4% of the total population. Men and women are affected with equal frequency. While it can begin at any age, it typically starts during adulthood. Psoriasis is not just a skin condition. It is a complex interaction between the immune system and the body's cells.

The underlying mechanism involves the immune system reacting to skin cells. This reaction causes inflammation and abnormal skin growth.

In some cases, skin injury can trigger new psoriatic changes at that specific spot. This is known as the Koebner phenomenon. Environmental factors can also trigger symptoms. These include seasonal changes, such as winter weather, and psychological stress. Certain infections or specific medications, like beta blockers and NSAIDs, can also play a role. The disease is thought to be a combination of genetic susceptibility and environmental responses.

There are several distinct types of psoriasis. Plaque psoriasis, or psoriasis vulgaris, is the most common form. It accounts for about 85% to 90% of all cases. It presents as raised, red patches covered with silvery-white scales. These plaques are often found on the elbows, knees, scalp, and back.

Guttate psoriasis is another type, characterized by small, droplet-shaped lesions called papules. This form is most common in children and young adults. It is often triggered by a streptococcal infection.

Pustular psoriasis involves raised bumps filled with noninfectious pus, known as pustules. This can be localized to the hands and feet or spread throughout the body.

Inverse psoriasis appears as smooth, inflamed patches in skin folds, such as the armpits or groin. Finally, erythrodermic psoriasis is a severe form. It involves widespread inflammation over more than 90% of the body surface. This form can be fatal because it disrupts the body's ability to regulate temperature.

Research into the genetics of psoriasis has identified several key factors. About one-third of people with the condition report a family history. Studies on twins show a strong genetic link. If one identical twin has psoriasis, there is a 70% chance the other will too. This is much higher than the 20% risk found in fraternal twins. Scientists have identified nine specific locations on chromosomes associated with the disease. These are called PSORS1 through PSORS9. The most important location is PSORS1, located on chromosome 6. This area is part of the major histocompatibility complex (MHC), which controls important immune functions. Variations in genes like HLA-Cw6, CCHCR1, and CDSN are also linked to the condition.

While there is no known cure, several treatments can manage the symptoms. About 75% of skin involvement improves with the use of topical creams alone.

Common treatments include steroid creams and vitamin D3 cream. Doctors may also use ultraviolet light therapy, also known as phototherapy. For more severe cases, immunosuppressive drugs like methotrexate are used. There are also biologic therapies that target specific immunologic pathways. The choice of treatment depends on the type and severity of the psoriasis.

Psoriasis can also affect the nails of the hands and feet. This occurs in 40% to 45% of people with skin psoriasis.

Nail changes may include small depressions called pitting, which occur in 70% of cases. Other changes include whitening, thickening of the skin under the nail, or discoloration known as salmon spots.

Additionally, up to 30% of individuals with psoriasis develop psoriatic arthritis. This is a chronic inflammatory condition that affects the joints. It can cause painful swelling, such as dactylitis, which makes fingers or toes look sausage-shaped.

Understanding psoriasis requires looking at how it connects to other health issues. The disease is associated with an increased risk of several other conditions. These include cardiovascular disease, Crohn's disease, and certain lymphomas. It is also linked to an increased risk of depression. By studying the genetic markers and immune pathways, researchers hope to find better ways to target the disease. The study of these molecular mechanisms helps scientists understand not just psoriasis, but other autoimmune diseases as well.