A system of practical medicine. By American authors. Vol. 4

by Unknown

Psoriasis.

Psoriasis may be defined as a chronic disease of the skin, characterized by reddish, dry, inflammatory, infiltrated patches, variable as to size, shape, and number, covered usually with abundant whitish, mother-of-pearl-colored, imbricated scales. It varies considerably in the degree of its development, but as a rule the lesions are numerous and their features clearly defined. It is the most uniform in its symptoms of all the diseases of the skin. It is therefore easy to recognize. In the first stage it appears as a small reddish spot, as large as a pinhead or a pea; it grows rapidly or slowly, and from the beginning shows signs of scaling, the scales being whitish, imbricated, and easily detached by scraping. They are reproduced readily, so that the lesion is usually well covered. In their early stages the lesions usually develop rapidly until their determinate size has been attained. The usual course is for the lesion to begin as a pinhead-sized spot, and grow to the size of a small or large coin. Several may appear side by side in close proximity, in which event they tend to coalesce, and to form larger, rounded, ovoidal, or figure-of-eight-shaped patches. Thus in time large surfaces of disease, the size of a hand or larger, may result. In other cases the lesions remain small, but through their great number may involve a considerable portion of the whole integument.

When typically developed, the lesions are of a bright- or dull-red color, and are covered with whitish, grayish, or pale-yellowish scales. The degree of inflammation varies with the case; at times it is slight, causing the lesions to assume merely a pale-pinkish, slightly inflammatory look; at other times it is more active, producing a decidedly inflammatory, strawberry- or raspberry-red hue. The majority of cases show a well-defined dull pinkish-red color of a cold inflammatory hue. The scaling, while usually active and abundant, is likewise variable; where the lesions are numerous and large it is constant, the scales being formed and shed rapidly from day to day; where the process is active, they are large, laminated, of a whitish, silvery, or mother-of-pearl-colored or slightly yellowish hue, varying somewhat with the locality involved. Sometimes they are heaped up. They are, moreover, easily detached, and can be readily picked or scraped off, leaving beneath a dry or very little excoriated, reddish surface. When deeply scratched, minute drops or points of blood, sometimes appear. They never exude serum. The lesions are, as a rule, circumscribed and sharply defined from the surrounding healthy integument, differing in this respect from similar patches of eczema. The skin between the lesions is perfectly healthy. In markedly inflammatory cases they occasionally possess a slightly raised border, and sometimes, especially in certain localities, as the hands, fissures form, as in eczema and syphilis.

The disease pursues an eminently chronic course, often lasting years or even throughout life, disappearing and recurring from time to time. Relapses at intervals of months or years are the rule, sometimes slight, at other times severe. It is a capricious disease. Usually it is better in summer than in winter, and in some cases it makes its appearance only during the latter season. It is generally unaccompanied by marked subjective symptoms, although this depends largely upon the degree of inflammatory action. In most chronic cases the itching and burning are either absent or slight, and when present are generally most annoying during the period that new lesions are appearing or old ones spreading. On the other hand, where the affection is highly inflammatory and running an acute, rapid course, both sensations, especially burning, may exist to an annoying degree. The disease is not contagious.

The eruption takes on different appearances according to the size and outline of the lesions, some of which require mention. They constitute the so-called varieties of the disease, but, strictly speaking, are forms rather than varieties. Thus, when the lesions are pinhead in size the form is termed punctata; when larger, the size of peas, guttata, from their resemblance to a drop of mortar; when still larger, the size of coins, they are designated nummularis, this being the form generally encountered. Sometimes the last-named lesions become more or less clear in the centre, and spread on their circumference after the manner of ringworm of the general surface, the condition being called circinata; at other times, more rarely, they assume a figured or ribbon-like form, causing them to have a serpentine, gyrate, or festooned appearance, termed gyrata. Commonly, however, when they grow to a large size they form, by the coalition of two or more lesions, irregularly-rounded patches, covering, it may be, a considerable area, the condition being called diffusa. The disease shows preference for certain regions, among which may be mentioned the extensor surfaces of the limbs, the elbows and knees, the scalp, and the trunk. The palms and soles and nails may also be invaded alone, or, as is usually the case, in connection with the disease upon other regions. It is usually symmetrical.

The causes of the disease seem to be varied, and are by no means well understood. It is met with, as a rule, in subjects whose general health is of the best, and who have hearty and strong constitutions, with no other ailment than the cutaneous manifestation. But cases are also encountered where the general condition is at fault: sometimes the system is below standard, as during lactation; in other cases the nervous system is depressed, as from some long-continued cause like mental worry. It occurs in both sexes, and usually makes its appearance in early adult life. It is seldom met with before the age of eight, and does not show itself in infants. In some cases it is inherited, but more frequently such is not the case. It occurs in all walks of life, being found among the rich and the poor in about like proportions. Statistics show it to be one of the most common diseases of the skin. It is of more frequent occurrence in some countries than in others. According to White's report of 5000 consecutive cases of skin disease observed in Boston, 152 cases of psoriasis were recorded, while Anderson in Glasgow reports 725 cases among 10,000 cases of skin disease, the difference being more than two to one in favor of Scotland. Diet in the majority of cases possesses but little influence over the disease.

The pathological process is one of the most defined and constant in cutaneous medicine. It is well marked throughout its course, and is subject to little variation. According to the most recent and reliable observations, it is held to be an inflammation induced by a hyperplasia of the rete mucosum. The views put forth by Auspitz and by Tilbury Fox have been substantiated by more recent observers. A. R. Robinson, and later Jamieson and Thin, have investigated the pathological anatomy of the disease with care, and have shown that the disease consists essentially of a hyperplasia of the rete mucosum, the increase taking place in the interpapillary portion of the layer. The growth extends downward, pressing upon the papillæ and corium, and setting up a variable degree of inflammation. In the later stages the superficial blood-vessels become dilated, more or less emigration of corpuscular elements occurring, the connective tissue especially in the neighborhood of the vessels becoming the seat of a round-cell infiltration. Effusion of serum, moreover, takes place, separating the connective-tissue bundles and fibres into an open meshwork. As the disease is vanishing there is a gradual return to the normal state, the hyperplasia, dilatation, and infiltration disappearing without traces. The hair is affected from the beginning in the form of hyperplasia of the external root-sheath, but the sebaceous and sweat glands are not found to be involved.

DIAGNOSIS.—The diagnosis, as a rule, offers no difficulties. The characteristic features are so constant and are usually so well marked that in ordinary cases errors are not likely to occur. When localized, as upon the scalp or upon the hands, it may be, however, readily confounded with other diseases. The general aspect of the eruption, the form of the lesions, the peculiar character of the scaling, the localities invaded, and the course of the process must be kept in view. It may be confounded with squamous eczema, especially where only one or two lesions are present, but the scales are usually more abundant, larger, and whiter than in eczema. The patches of psoriasis, moreover, are circumscribed, often sharply defined, and are always dry. In eczema there is not infrequently a history of moisture; itching is also generally an annoying symptom, much more marked than in psoriasis.

The papulo-squamous syphiloderm at times closely resembles psoriasis, especially as it occurs upon the palms and soles. Symmetry usually exists in psoriasis, but in syphilis it is often lacking, even in connection with disease of the palms and soles. Apart from the question of a history of syphilis, it will be found that psoriasis generally involves more surface, and in a more disseminate form, than the syphilitic eruption; also, that the scales are whiter, larger, and more copious than in syphilis. The color of the lesions in both diseases is similar, but in psoriasis it is pinker or redder, and free from the yellowish, brownish, ham-colored tint that generally characterizes the later syphilitic eruptions. The infiltration and thickening of the skin in a psoriatic patch are less than in syphilis, this observation being a valuable point in the diagnosis. The character of the inflammatory product in the diseases is different, that of psoriasis being simpler and less dense and firm. Finally, the course of psoriasis is peculiar, the lesions always manifesting the same general characters, often disappearing spontaneously and again reappearing.