Psoriasis is a chronic skin condition characterized by itchy or burning, clearly demarcated patchy skin lesions on a reddened base covered with silvery scales. It affects about 3 percent of the U.S. population, mainly adults.
Psoriasis is generally thought to be an immunologically mediated condition which can be worsened by stress, infections, certain drugs and skin dryness. The mechanism is an interaction of certain targets on the surface of the keratinocytes (skin cells) with T-lymphocytes (a subset of white blood cells) to produce an inflammatory response. The products of this interaction, chemokines and cytokines, also lead to very rapid cell turnover with heaping up and flaking of skin cells. At the same time, the swelling, redness, heat and burning, itching or pain is produced. A strong family history and discovery of genetic links has confirmed a genetic predisposition in certain cases. There are still a lot of cases without obvious causes.
Presentation
Plaque (or discoid) psoriasis is the most common, which presents as the classical patches on the elbows, knees and trunk.
Guttate psoriasis typically follows an attack of streptococcal sore throat. It is more widespread in distribution, appearing as teardrop lesions all over the body.
Pustular psoriasis presents with widespread truncal non-infective pustular or bullous lesions, which can be mistaken for a bacterial skin infection.
Erythrodermic psoriasis is a generalized version, with weeping, burning lesions that can lead to dehydration and secondary infection, since the usual skin cover is lost on a wide scale.
Inverse psoriasis occurs under the breasts and in moist areas of the body like the groin. This type shows no scales, since this area is usually moist.
Joint, nail and mucosal involvement is also common as the disease progresses, usually in a relapsing trend.
Mechanism of Pruritus (Itching)
The interaction of keratinocytes with T-lymphocytes leads to release of chemical mediators of the inflammatory response. These chemicals excite local free nerve endings in the skin to produce the pain usual in inflammation. In a poorly understood way, skin nerve terminals for pain also produce a sensation of pruritus (itching) when stimulated in certain conditions.
Sometimes, psychological reactions accentuate the sensation, leading to lower thresholds and worsening of the itching.
The cessation of the itching or burning is typically the first response to suitable treatment or, in some cases, the first sign of a flare up.
Outlook
There are many effective remedies or treatment combinations for psoriasis today, with improving quality of life amongst patients with this condition. There are also many avenues of research towards better treatment options as the disease process is understood better.
