PSORIASIS is a disease of the skin distinguished by slightly raised red patches of various extent and form, and generally covered with whitish scales. Several varieties of the disease have received different names, according to the form and severity of the eruption in each, and many others, according to the part chiefly alone affected. The former varieties are Psoriasis guttata, P. diffuse, P. grata, and P. inveterata ; among the latter are P. ophthalmica, P. palmaria, &c.
Psoriasis guttata is a mild form of the disease, consisting of small red patches two or three lines in diameter covered with very fine white scales. It occurs in various extent on all parts of the body, but most rarely on the face. At first small red spots appear, and soon after present white scales at their centres; then the spots gradually enlarge and the scales increase in number, till the redness begins to fade at tho centre, and as the scales fall off, the skin slowly assumes its natural colour. The eruption is attended by a moderate itching, and by very slight symptoms of general disorder.
P. d Vasa is in every respect a more severe form of the disease. Tho spots are large and irregular, and often confluent, and covered with thick scaly incrustations. It appears most frequently on the limbs and around the joints, often covering the whole of a limb with one scaly or raw-looking patch, and sometimes occurring at once and with equal severity on several parts of the body. The skin beneath the scales is very tender and irritable; it often cracks and discharges a thin ichor, which concretes about the fissures, and is attended by con siderable pain and irritation, and some constitutional disturbance. Tho eruption often breaks out successively in different parts of the body, so that it is common for the disease to be protracted for several months and even for years.
P. inreterata is only (as its name implies) a yet less curable form of the same disease. The skin has its whole texture thickened and hard, its surface is covered by a furfuraceous deposit, and in the neighbour hood of the joints it is often very deeply and painfully cracked. The preceding forms are commonly met with in those who are otherwise in pretty good health ; but this rarely occurs, except in those whose constitutions are enfeebled by long disease or want.
P. orata is a slight but very rare variety, distinguished by the patches occurring in stripes of a singularly tortuous or serpentine form.
Of the local varieties of Psoriasis, the most interesting is that which occurs on the palms of the hands, and which, being most frequent in those who work with light powders, and other irritating substances, is commonly called bakers, or bricklayers, or washerwomen's itch.
Psoriasis, in all its forms, is difficult of cure. The general con dition of the health being corrected by the means that in each case seem appropriate, the remedy which is most frequently successful in cases of long standing is arsenic, in the form of from three to five drops of the Fowler's solution, three times a day, for an adult. Active purging is also often useful, especially in recent cases and in young subjects. Another good remedy is tincture of cantharides, in doses of from three to five drops (for an adult) in water once or more in the day ; but the effects of both this and the arsenic require to be carefully watched during their administration, and they must be discontinued as soon as they appear to produce any sickness or heat in the stomach.
The arsenic should be taken at meals, if not it is more likely to produce sickness. In addition to these, various other internal means have been recommended, as decoctions of dulcamara, mezereon, and orchis, antimony; sulphur, &c. Indeed, in many cases it is found necessary to try one means after another without any rule, till one is found which produces benefit. External remedies are generally of less value than internal. The most approved are vapour and sulphur baths, and ointments or lotions containing very small quantities of nitrate of mercury, or white precipitate, or creasote, or alkalies. These however can only be employed in the later stages of the disease : in the earlier, the mildest fomentation give relief, and all kinds of irritants must be carefully avoided.