Psoriasis In-Depth

Psoriasis is a chronic skin disorder marked by periodic flare-ups of sharply defined red patches, covered by a silvery, flaky surface. The primary disease activity leading to psoriasis occurs in the epidermis, the top five layers of the skin.

• The process starts in the basal (bottom) layer of the epidermis, where keratinocytes are manufactured.
• Keratinocytes are immature skin cells that produce keratin, a tough protein that helps form hair and nails as well as skin. In normal cell growth, keratinocytes mature and migrate from the bottom (basal) layer to the surface and are shed unobtrusively. This process takes about a month.
• In psoriasis, however, the keratinocytes multiply very rapidly and travel from the basal layer to the surface in only about 4 days. The skin cannot shed these cells quickly enough, so they accumulate in thick, dry patches, or plaques.
• Silvery, flaky areas of dead skin build up on the surface of the plaques and are shed. The underlying skin layer, the dermis, is red and inflamed (swollen).
• The dermis contains nerves, blood vessels, and lymphatic vessels. They supply the abnormally multiplying keratinocytes with their blood, and also transport strong immune factors that cause the underlying inflammation and redness.

Various forms of psoriasis exist. Some can occur independently or at the same time as other variants, or one may follow another. The most common type is called plaque psoriasis, also known as psoriasis vulgaris.

Plaque Psoriasis

Plaque psoriasis is the most common form of psoriasis, and causes skin patches with the following characteristics:

• The patches start off in small areas, about one-eighth of an inch in diameter. They usually appear symmetrically (in the same areas on opposite sides of the body).
• The patches gradually enlarge and develop thick, dry plaque. If the plaque is scratched or scraped, bleeding spots the sizes of pinheads appear underneath (this is known as the Auspitz sign).
• Some patches may become ring shaped (annular), with a clear center and scaly raised borders that may be wavy and snake-like.
• Eventually separate patches 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 (known as geographic plaques because they resemble maps).

Location of Plaque Psoriasis:

• Patches most often occur on the elbows, knees, and the lower back.
• About half of patients develop psoriasis on the scalp. Many patients have only a few patches in this location. In some cases, however, psoriasis can cover the scalp with thick plaques that may even extend down from the hairline to the forehead. It rarely affects the face in adulthood, however.
• Patches also can appear on the palms and soles, in the genital areas of both men and women, above the pelvic bone, and on the thighs and calves.
• In children, psoriasis is most likely to start in the scalp and spread to other parts of the body. Unlike in adults, it also may occur on the face and ears.

Course of Plaque Psoriasis. Plaque psoriasis may persist for long periods. More often it flares up periodically, triggered by certain factors, such as cold weather, infection, or stress.

Psoriatic Arthritis

Psoriatic arthritis (PsA) is an inflammatory condition characterized by stiff, tender, and inflamed joints. About 80% of PsA patients have psoriasis in the nails. Arthritic and skin flare-ups tend to occur at the same time. It is not clear whether psoriatic arthritis is a unique disease or a genuine variation of psoriasis, though evidence suggests they are both caused by the same immune system problem.

Location of Joint Pain Psoriatic Arthritis. Some experts define five forms of PsA. They differ in the location and severity of the affected joint:

• Symmetric PsA: Symmetric arthritis occurs in the same location on both sides of the body. It usually affects multiple pairs of joints, and, in about half of the cases, the condition will progress. The condition is very similar to, but less disabling than, rheumatoid arthritis. The psoriasis itself is often severe.
• Asymmetric PsA: Asymmetric PsA involves periodic joint pain and redness, usually in only one to three joints, which can be the knee, hip, ankle, wrist, or one or more fingers. The pain does not occur in symmetric locations.
• Distal Interphalangeal Predominant (DIP): DIP involves the joints of the fingers and toes closest to the nail, and occurs in about 5% of PsA cases.
• PsA in the Spine: Inflammation in the spinal column (spondylitis) is the primary symptom in about 5% of PsA cases. Such patients may experience stiffness and burning sensations in the neck, lower back, sacroiliac, or spinal vertebrae. The spine can be involved in up to three-quarters of all patients with PsA, even though stiffness and burning sensations in these areas are not the primary symptoms. When it affects the spine, psoriatic arthritis most frequently targets the sacrum (the lowest part of the spine). Movement is difficult.
• Arthritis Mutilans: This is a severe, deforming and progressive arthritis that affects less than 5% of PsA cases. It principally affects the small joints of the hands and feet, but it can also be found in the neck and lower back. Arthritic and skin flares and remissions tend to coincide.

Course of Psoriatic Arthritis. Although patients with psoriatic arthritis tend to have mild skin symptoms, the disease is systemic, affecting the whole body. PsA, therefore, is more serious than the more common plaque psoriasis.

Infrequently, the course of PsA has been associated with a syndrome known by the acronym SAPHO, whose letters form the symptoms:

• Synovitis (inflammation in the joints)
• Acne
• Pustule eruptions
• Hyperostosis (abnormal bony growths)
• Osteolysis (bone destruction)

Prevalence of Psoriatic Arthritis. Estimates on its prevalence among those with psoriasis range from 2% to as high as 42%. AIDS patients and those with severe psoriasis are at higher risk for developing PsA.