Clinical Description of Psoriasis

Chapter 2 – Clinical Description of Psoriasis The normal life span of a skin cell is about a month, at which time the cell is shed off of the body.  For a person with psoriasis, a skin cell matures in about three to four days, with the lower level of skin cells dividing more rapidly than usual.  This means that dead skin cells cannot be shed at a fast enough rate, and these cells accumulate in thick patches at the outermost layer of the skin, which we call the epidermis.  Since there are more skin cells than can normally fit in this area, the skin becomes raised and some of the cells form scales that stay somewhat attached to the skin.  This skin inflammation is the hallmark of psoriasis, though the appearance of the inflammation may vary. There are five major forms of psoriasis.  These differ in the duration, location, intensity and shape of the patches.  The most common form is plaque psoriasis, with raised, inflamed red lesions covered by silvery white scales, which are just the buildup of dead skin cells that have not yet been shed from the skin.  These areas are most often found on the trunk, elbows, knees, scalp, and finger or toe nails.   The affected areas itch or are sore, and may even occur on the genital area or the soft tissue inside of the mouth.  Ninety percent of psoriasis patients have plaque psoriasis. A second form is pustular psoriasis, which have small pus filled blisters (similar to the whiteheads that teenagers get on their faces) spread over a larger area of the skin.  These are often itchy and painful.  These may be found all over the body, or confined just to the palms and soles of the body.  Pustular psoriasis has a rapid onset, with the blisters appearing within a few hours after the skin becomes red and tender.  The blisters do not last longer than a day or two, but may reappear every few days or weeks.  This form of psoriasis may also cause fever, chills, fatigue, weight loss, and intense itching.  This is a relatively rare form of psoriasis.   The rarest form of the disease is  erythrodermic psoriasis, and may cover the whole body with a red, peeling, itchy or burning rash.   An outbreak of this type may be caused by a strong sunburn, by certain types of steroids or other medications, or as a secondary result from a different type of psoriasis left untreated.   A type of psoriasis that affects children more than other people is known as guttate psoriasis, and consists of many small, red, drop-like scaly macules that spread quickly over a wide area of skin. It is not common to find this type in people over the age of thirty.  This often shows up after an infection such as strep throat.  The raised areas of skin are not as prominent, and are marked by many small, water droplets shaped sores.  This may happen only once, and may go away on its own.  Children or young people with recurrent respiratory infections may have repeated episodes of guttate psoriasis. One type of psoriasis that does not have thick scales is inverse psoriasis, which is found in the armpit, under the breast, in skin folds, around the groin, in the cleft between the buttocks and around the genitals. The skin most often looks irritated and pink, but doesn’t have the normal rough appearance of other forms of psoriasis.  This is more common in people with excess weight, and gets worse with sweating and friction against the skin. A particular case of psoriasis may be classified as a mild, moderate, or severe case.  If the patches and scaling cover less than five or ten percent of the body, then it is a mild case.  If the patches of scaly, irritated skin cover between ten and twenty percent of the body, it is moderate, and more than that is considered to be a severe case. In five percent of all psoriasis sufferers, arthritis will develop. This condition is called psoriatic arthritis. Arthritis is when a joint becomes inflamed, and is usually accompanied by pain, swelling and changes in the structure of the joint.  This form of the disease can become worse and lead to eye problems such as conjunctivitis.   Though it isn’t often as debilitating as other forms of arthritis, it can cause stiffness and joint damage that might lead to permanent deformation of the joints affected. The skin affected by psoriasis has a very distinctive look.  It is raised and reddened, with a rich, full salmon color to the skin.  If the affected area is on the palms of the hands, the feet, or over a joint such as the elbow or the knee, the skin can split and bleed.  These are known as fissures, and are more susceptible to infection.   Sometimes the plaques of psoriasis are surrounded by what looks like a ring or halo, and psoriasis on the legs may have a blue tint to it.  If the silvery scales are removed from the skin, the underlying skin is smooth, red, and shiny, often with small areas that bleed.  If the skin appears red and seems like it has little drops on it, it is likely to be guttate psoriasis.  This often occurs after a streptococcal infection. Psoriasis commonly affects the nails in those people who have plaque psoriasis.  They frequently have small ridges, indentations, or pits in the nail itself.  The nail might be discolored, and sometimes can separate from the nail bed.  In very severe cases, the nail itself may crumble. When a child gets psoriasis it may look slightly different than pictures of the same type of psoriasis in adults.  The raised areas are not as thick, and the skin doesn’t have as may scales as adult skin does.  Psoriasis may occur as early as infancy, and may appear in the diaper area of the child.  It occurs more frequently on the face than it does in adult flare-ups. The cause of psoriasis begins with a type of white blood cell called a T lymphocyte or T cell. It is the T cell’s function to circulate throughout the body and detect any foreign substances in the body.  When it encounters one, such as a virus or bacterium, it will destroy these substances in order to protect the body.   T cells function as the soldiers of the body in order to detect cells or substances that need to be eliminated. However, the T cells of someone with psoriasis detect and attack the healthy skin cells just as if they were invaders in the body.  This attack by the T cells triggers other immune responses of the body such as directing more T cells to the site, more white blood cells, and also producing more healthy skin cells.  This forces other skin cells to move to the outer layer of the skin, the epidermis, too quickly, in just a matter of days.    Dead white blood cells and the increased number of skin cells can't be shed quickly enough by the body, and become the patches of thick, scaly skin that is characteristic of psoriasis.  This T cell behavior generally continues unless some kind of treatment stops the cycle of T cell detection and attack.  Physicians are not sure of the underlying reason that these T cells consider skin cells as foreign invaders, though they are researching both genetic and environmental factors.  Psoriasis is definitely not a communicable disorder.