Psoriasis is a chronic inflammatory skin condition that begins when areas of the skin produce new skin cells more rapidly than the normal rate, which causes thickening of the skin’s stratum corneum. These areas—called plaques-- are characteristically pinkish- red and are covered by a silvery scale. “Psoriasis” is derived from the Greek word psoria, which means “itch”, and the degree of itchiness can range from mild to severe. In 50 percent of cases, the nails are also involved. Severe variants of psoriasis can cause arthritis in joints. The cause is unknown, although there is evidence that genetics and the immune system may be involved. Although psoriasis is a chronic disease with no permanent cure, there are many types of treatments that help the patient gain control over the disease.
The normal time it takes for the epidermis of the skin to renew itself is 28 to 30 days. In patients with psoriasis, this cycle can be compressed to as short as three days. The new cells that build up do not have time to shed, and the result is a thickened, scaly plaque with distinct borders separating it from the surrounding normal skin. When the scale is removed, the appearance of tiny droplets of blood on the plaque is called the “Auspitz sign”. Plaques are typically located on the elbows, knees, scalp, and the intergluteal cleft between the buttocks. However, psoriasis can occur anywhere on the skin surface.
The prevalence of psoriasis in the general population is approximately one in 167 people. Psoriasis can develop at any age, but it usually begins between age 15 and 35. Men and women are affected equally. No one knows for sure what causes it. More than one-third of patients with psoriasis have an immediate relative with the disease, which supports a genetic cause. Recent research points to an abnormality of the immune system’s T-cells as a culprit.
Psoriasis usually starts gradually, but sometimes it can have a sudden onset. The disease usually waxes and wanes. Flare- ups can be caused by trauma to the skin (Koebner’s phenomenon), emotional stress, and medications such as lithium, anti-malarial drugs, beta-blockers, and non-steroidal anti-inflammatory drugs (NSAIDs). About one percent of patients with AIDS develop very severe psoriasis, and in some cases psoriasis is the first sign of the disease. Patients often note that their psoriasis is better in the summer, perhaps due to a favorable effect from sunlight.
Nails can be involved in as many as 50 percent of patients with psoriasis. Pitting (small depressions on the nail plate) is the most common condition. Another condition, onycholysis, or separation of the nail plate from nail bed, can also occur. This happens when a psoriatic plaque forms in the nail bed, lifting and separating the overlying nail plate from the nail bed.
Reviewed by: Michael Fuller, MD