Psoriasis

Psoriasis is a constitutional disease, characterized by cutaneous lesions of the squamous type.

This affection may appear in the early years of childhood, or at almost any later period up to and including so-called middle life. It rarely appears at either of the extremes, that is, during infancy or old age.

Its first manifestations usually take the form of small red papules, soon decked with a white scale. These may be few and scattered, or many and closely aggregated. The scaly papules increase at their periphery, becoming flattened patches from the size of a pea to that of a coin or even larger. When the progress of the disease continues, neighbouring patches encroach on each other, and in time coalesce, giving rise to irregular gyrate forms. Coincident with the peripheral extension there is an increase in the infiltration or thickening of the skin, and the scales become large, imbricated, and more or less adherent. On forcible removal of the scales, a red infiltrated patch is brought to light, on the surface of which minute droplets of blood may be seen. After the disease has attained its maximum development, which may include the greater" portion of the surface, it may undergo a gradual involution and disappear. This is the course followed in not a few cases of mild type. A single attack of this sort, however, is exceedingly rare. In almost every instance the eruption reappears after a shorter or longer interval. In not a few cases of mild type there will be an appearance of the lesions at the beginning of the cold and a disappearance of them at the begin­ning of the warm seasons. In cases even where the eruption is caused to disappear by treatment there is the same tendency to return, and this relapsing feature of the disease is one of its most important and most annoying characteristics. To such an extent is this true, that even with the most judicious treatment there is no certainty of a radical cure. As a rule, if a person once has psoriasis, he may expect to have it always, that is, with certain intervals of freedom. The reverse of this is rare, as it is extremely exceptional for a patient to recover permanently, or to enjoy immunity for a term of years.


The subjective symptoms are usually unimportant, amounting at   most   to   a   moderate   degree   of   pruritus, though in many cases this is not sufficient to be complained of by the patient. The eruption frequently exhibits a more or less symmetrical disposition, and prefers the extensor surface, with aspecial predilection for the elbows and knees. The upper half of the body usually presents more lesions than the lower. It very rarely affects the palms or soles. When situated on the genitals it may excite an analogous condition of the mucous membrane.


The features of the disease are themore characteristic if account be taken of its negative signs; for in it there is an entire absence of any discharge, vesiculation, or pustulation throughout the whole course of the disease. The characteristics above described constitute a primary condition.

The eruption affects (by preference) certain parts of the skin whose epithelium is thick, especially the elbows and knees. It may be partial or general. At the outset the disease may be attended by more or less pruritus. The increase of the patches is by centrifugal growth, and there is oftentimes a slightly red margin; the scales are shed, to be again replaced by others; in chronic cases the derma itself becomes very distinctly infiltrated and thickened. The general health is often apparently good. The disease is non-contagious, runs a chronic course, and is very prone to recurrence.