The erythematous and vesicular varieties are the most favorable.

State the treatment to be advised.

There are no special remedies. Const.i.tutional treatment must be conducted upon general principles. A free action of the bowels is to be maintained. In occasional instances a.r.s.enic in progressive doses seems of value. Externally protective and antipruritic applications, such as are employed in the treatment of eczema and pemphigus, are to be employed:--

[Rx] Ac. carbolici, ....................... [dram]j-[dram]ij Thymol, .............................. gr. xvj.

Glycerinae, ........................... [Oz]ss-[Oz]j Alcoholis, ........................... f[Oz]ij Aquae, q.s., ......... ad ............. Oj. M.

Other valuable applications are: lotions of carbolic acid, of liquor carbonis detergens, of boric acid; alkaline baths, mild sulphur ointment and carbolized oxide-of-zinc ointment, and dusting-powders of starch, zinc oxide, talc and boric acid. A two- to ten-per-cent. ichthyol lotion or ointment is sometimes of advantage; thiol employed in the same manner has also been commended.

Psoriasis.

Give a definition of psoriasis.

Psoriasis is a chronic, inflammatory disease, characterized by dry, reddish, variously-sized, rounded, sharply-defined, more or less infiltrated, scaly patches.

[Ill.u.s.tration: Psoriasis.]

At what age does psoriasis usually first make its appearance?

Most commonly between the ages of fifteen and thirty. It is rarely seen before the tenth year, and a first attack is uncommon after the age of forty.

Has psoriasis any special parts of predilection?

The extensor surfaces of the limbs, especially the elbows and knees, are favorite localities, and even when the eruption is more or less general, these regions are usually most conspicuously involved. The face often escapes, and the palms and soles, likewise the nails, are rarely involved. In exceptional instances, the eruption is limited almost exclusively to the scalp.

Are there any const.i.tutional or subjective symptoms in psoriasis?

There is no systemic disturbance; but a variable amount of itching may be present, although, as a rule, it is not a troublesome symptom.

Describe the clinical appearances of a typical, well developed case.

Twenty or a hundred or more lesions, varying in size from a pin-head to a silver dollar, are usually present. They are sharply defined against the sound skin, are reddish, slightly elevated and infiltrated, and more or less abundantly covered with whitish, grayish or mother-of-pearl colored scales. The patches are usually scattered over the general surface, but are frequently more numerous on the extensor surfaces of the arms and legs, especially about the elbows and knees. Several closely-lying lesions may coalesce and a large, irregular patch be formed; some of the patches, also, may be more or less circinate, the central portion having, in a measure or completely, disappeared.

Give the development and history of a single lesion.

Every single patch of psoriasis begins as a pin-point or pin-head-sized, hyperaemic, scaly, slightly-elevated lesion; it increases gradually, and in the course of several days or weeks usually reaches the size of a dime or larger, and then may remain stationary; or involution begins to take place, usually by a disappearance, partially or completely, of the central portion, and finally of the whole patch.

Describe the so-called clinical varieties of psoriasis.

As clinically met with, the patches present are, as a rule, in all stages of development. In some instances, however, the lesions, or the most of them, progress no further than pin-head in size, and then remain stationary, const.i.tuting _psoriasis punctata_; in other cases, they may stop short after having reached the size of drops--_psoriasis guttata_; in others (and this is the usual clinical type) the patches develop to the size of coins--_psoriasis nummularis_. In some cases there is a strong tendency for the central part of the lesions to disappear, and the process then remain stationary, the patches being ring-shaped--_psoriasis circinata_; and occasionally several such rings coalesce, the coalescing portions disappearing and the eruption be more or less serpentine--_psoriasis gyrata_. Or, in other instances, several large contiguous lesions may coalesce and a diffused, infiltrated patch covering considerable surface results--_psoriasis diffusa, psoriasis inveterata_.

[Ill.u.s.tration: Fig. 17. Psoriasis.]

Is the eruption of psoriasis always dry?

Yes.

What course does psoriasis pursue?

As a rule, eminently chronic. Patches may remain almost indefinitely, or may gradually disappear and new lesions appear elsewhere, and so the disease may continue for months and, sometimes, for years; or, after continuing for a longer or shorter period, may subside and the skin remain free for several months or one or two years, and, in rare instances, may never return.

[Ill.u.s.tration: Fig. 18. Psoriasis.]

Is the course of psoriasis influenced by the seasons?

As a rule, yes; there is a natural tendency for the disease to become less active or to disappear altogether during the warm months.

What is known in regard to the etiology of psoriasis?

The causes of the disease are always more or less obscure. There is often a hereditary tendency, and the gouty and rheumatic diathesis must occasionally be considered potential. In some instances it is apparently influenced by the state of the general health. It is a rather common disease and is met with in all walks of life.

Is psoriasis contagious?

No. In recent years the fact of its exhibiting a family tendency has been thought as much suggestive of contagiousness as of heredity.

What is the pathology?

According to modern investigations, it is an inflammation induced by hyperplasia of the rete mucosum; and it is beginning to be believed that this hyperplasia may have a parasitic factor as the starting-cause.

With what diseases are you likely to confound psoriasis?

Chiefly with squamous eczema and the papulo-squamous syphiloderm; and on the scalp, also with seborrh[oe]a. It can scarcely be confounded with ringworm.

How is psoriasis to be distinguished from squamous eczema?

By the sharply-defined, circ.u.mscribed, scattered, scaly patches, and by the history and course of the individual lesions.

In what respects does the papulo-squamous syphiloderm differ from psoriasis?