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 constitutional 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, hyperæmic, 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, constituting 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.
Fig. 17.