This section is from the book "A Treatise On The Materia Medica And Therapeutics Of The Skin", by Henry G. Piffard. Also available from Amazon: A Treatise On The Materia Medica And Therapeutics Of The Skin.
Psoriasis is a constitutional disease, characterized by the appearance on the skin of scaly patches of varying size. The scales are silvery white, thick and imbricated, and rest upon a thickened and infiltrated base of deep red color. The deeper scales are firmly attached, and on forcible removal expose little bleeding points. The patches vary in size, in configuration, and in locality, and on these peculiarities a number of varieties have been based by different authors. At the very commencement minute, slightly raised points become visible. These are soon covered with scales, and the affection, in this stage and condition, may be termed Psoriasis punctata. These increase in size, and may resemble a drop of wax or of mortar, and then constitute P. guttata. If they increase until they have attained the size of a coin the name P. nuntmulata is applied. If several of them coalesce so as to cover an extended surface the term P. diffusa is employed. If the spots heal in the centre, leaving a ring, the name P. annularis may be used. Some English writers apply the term Lepra, or lepra vulgaris, to this form. If a large patch, formed by the confluence of several smaller ones, heals everywhere except at the borders, these latter may have a gyrate or sinuous outline, and the name P. gyrata is given. Lastly the expression P. universalis indicates that the greater part of the surface has been invaded. It will be readily perceived that these several so-called varieties are not such in reality, but simply indicate different stages, etc., of the disease.
Psoriasis may occur anywhere on the surface from the scalp to the sole of the foot, but its favorite seats or points of election are the elbows and knees. The disease is not contagious.
Whether scantily developed or extensive, Psoriasis is essentially chronic, and when unrelieved by treatment often lasts for months and sometimes for years; and even when caused to disappear it is ever ready to return on the slightest or even without any apparent provocation. It is usually worse in winter than in summer, and may disappear spontaneously during the hot months, to return again when the cold weather sets in. This tendency to relapse is one of the most prominent and striking features of the disease. The lesions in typical cases are always dry, never exhibiting vesicles or pustules, and never exuding moisture or forming crusts. The superficial scales are less adherent than the deeper ones, and may be removed by the slightest friction. They are, however, quickly renewed, and in a few days are as thick as before removal. In extensive cases the amount of desquamation may be very great, reaching even to a teacupful of scales in twenty-four hours. After this condition has lasted for an indefinite period, retrogressive changes may occur spontaneously, or as the result of treatment. In either case the desquamation lessens, the infiltration diminishes, and the color fades out without leaving scar or mark to indicate the site of the previous eruption. In some cases recovery commences at the centre of a patch, and gradually progresses outward to the margins, which are the last to disappear. Pruritus of moderate severity not unfrequently accompanies the eruption. Sometimes this symptom is absent.
In the vast majority of cases no difficulty will arise in connection with the recognition of this affection. Occasionally, if limited in extent and situated on parts that are naturally moist, as about the geni-tals, Psoriasis may exhibit a close resemblance to Eczema. As a rule, however, patches will be found on other parts and exhibit typical features, thus enabling a diagnosis to be made. The only serious difficulty that is apt to arise is in distinguishing between Psoriasis and a scaly Syph-ilide. The previous history will sometimes settle the matter in case of doubt, while at other times thorough analytical examination of the lesion will be requisite. If on inquiry it is ascertained that the present eruption is the first distinctly scaly one that the patient has had, but that within a year or two he has had several other eruptions of differing character, the presumption is in favor of Syphilis. If, on the other hand, the patient states that he has had a similar scaling on previous occasions, and for a number of years, the diagnosis of Psoriasis is almost certain.
As regards the lesion it may be stated that, as a rule, the infiltration is not as great in squamous Syphilides as in Psoriasis, the scales too, are larger but not heaped up, nor are there so many of them in the former as in the latter disease. Further, the scales usually entirely cover the infiltrated base in Psoriasis, while a little reddish ring or margin generally surrounds the scales in Syphilis. These features, together with such history as can be got, will usually enable a correct diagnosis to be made.
Psoriasis pertains to the Rheumic diathesis, and the fons et origo, and the predisposing causes of the affection must be there sought. The exciting causes are obscure. A great number have been mentioned by authors, but hardly one of them will be found to hold good except in a limited number of cases. It may be noticed, however, that the eruption sometimes appears on women during the periods of gestation and lactation, though absent in the same patients at other times.
Though never of itself fatal, nor, so far as I know, provocative of other serious disease, the prognosis as regards a permanent cure is decidedly unfavorable, in consequence of its unrelenting tendency to relapse. Hebra, in fact, states that it is incurable, and perhaps it is when treated by the Vienna method. My own experience, however, and that of other American, English, and French dermatologists, is more favorable, and it may be stated that, in a certain proportion of cases, patients will, after a prolonged and judicious treatment and proper care on their own part, go for many years, if not for life, without a return of the disease.