This affection may appear in the early years of childhood, or at almost any later period up to and including so-called middle life. It rarely appears at either of the extremes-that is, during infancy or old age.
Its first manifestations usually take the form of small red papules, soon decked with a white scale. These may be few and scattered, or many and closely aggregated. The scaly papules increase at their periphery, becoming flattened patches from the size of a pea to that of a coin or even larger. When the progress of the disease continues, neighboring patches encroach on each other, and in time coalesce, giving rise to irregular gyrate forms. Coincident with the peripheral extension there is an increase in the infiltration or thickening of the skin, and the scales become large, imbricated, and more or less adherent. On forcible removal of the scales, a red infiltrated patch is brought to light, on the surface of which minute droplets of blood may be seen. After the disease has attained its maximum development, which may include the greater portion of the surface, it may remain stationary for an indefinite period, or may undergo a gradual involution and disappear. This is the course followed in not a few cases of mild type. A single attack of this sort, however, is exceedingly rare. In almost every instance the eruption reappears after a shorter or longer interval. In not a few cases a mild type there will be an appearance of the lesions at the beginning of the cold and a disappearance of them at the beginning of the warm seasons.
In cases even there the eruption is caused to disappear by treatment there is the same tendency to return, and this relapsing feature of the disease is one of its most important and most annoying characteristics. To such an extent is this true, that even with the most judicious treatment there is no certainty of radical cure. As a rule, if a person once has psoriasis, he may expect to have it always- that is, with certain intervals of freedom. The reverse of this is rare, as it is extremely exceptional for a patient to recover permanently, or to enjoy immunity for a term of years.
The subjective symptoms are usually unimportant, amounting at most to a moderate degree of pruritus, though in many cases this is not sufficient to be complained of by the patient.
The eruption frequently exhibits a more or less symmetrical disposition, and prefers the extensor surface, with a special predilection for the elbows and knees. The upper half of the body usually presents more lesions than the lower. It very rarely affects the palms or soles. When situated on the genitals it may excite an analogous condition of the mucous membrane.
The features of the disease are the more characteristic if account be taken of its negative signs; for in it there is an entire absence of any discharge, vesiculation or pustulation throughout the whole course of the disease. The characteristics above described constitute a primary condition.
The eruption affects (by preference) certain parts of the skin whose epithelium is thick, especially the elbows and knees. It may be partial or general. At the outset the disease may be attended by more or less pruritus. The increase of the patches is by centrifugal growth, and there is oftentimes a slightly red margin; the scales are shed, to be again replaced by others; in chronic cases the derma itself becomes very distinctly infiltrated and thickened. The general health is often apparently good. The disease is non-contagious, runs a chronic course, and is very prone to recurrence.
It is customary to make certain local varieties; they are:
Psoriasis capitis.-The head is one of the commonest seats of the disease, next to the elbows and the knees; the whole scalp may be affected, or there may be only one or two small points of eruption; when extensive, the disease travels on to the forehead, forming a kind of fringe along it at the upper part. There is co-existent disease elsewhere. The hair on the scalp thins out frequently when psoriasis attacks it.
Psoriasis faciei.-In this local variety of psoriasis, the patches are often circular; they are less hyperaemic, less thick, and less scaly than when the disease attacks other parts of the body, and they present consequently much similarity to tinea circinata, except that typical patches of the disease are seen in other parts of the body.
Psoriasis palmaris and psoriasis plantaris are important local varieties. These local varieties are infinitely rare. Of course, instances of so-called psoriasis palmaris and plantaris are common enough, but they are practically always syphilitic. Non-syphilitic psoriasis may occur, though rarely, in connection with general psoriasis. But when such a condition exists as the sole disease, it is syphilitic and nothing else, and the concomitance of sore tongue and other evidences of constitutional syphilis at once make the diagnosis certain. The skin in the affected parts is generally thick, and dry, harsh, discolored; the scaliness is not very marked, but the superficial layers peel off from time to time. Presently the surface cracks and fissures, and healing is very tardy; occasionally the surface bleeds. The muscular movements of the hand may be painful.
Psoriasis unguinum is mostly a complication of the inveterate form of psoriasis, but it may exist alone. The nails (and several are usually affected) lose their polish. and soon become opaque, thickened, irregular, and brittle; they are then fissured and discolored in lines (from dirt), their matrix becoming scaly.
Psoriasis also affects the scrotum and prepuce occasionally; the parts are swollen, red, hard, tender, scaly, fissured more or less, and give exit to a thin secretion, which adds to the scaliness; there are pain pruritus; and the local mischief may be the sole, or part only, of general disease.
Psoriatic syphilides.-Nozo asserts that psoriatic syphilides always indicate the presence of a grave variety of syphilis and that they occur most commonly in cachectic subjects. In some cases they may appear as late manifestations of the disease; and their development is favored by old age, alcoholism, congenital or acquired dryness of the skin, and perhaps, also, by gout. Cases occur concerning which even the most expert diagnostician may be in doubt as to whether the eruption is the ordinary psoriasis or a specific eruption.
When psoriasis is in progress of cure, the scales lessen and the reddened elevated surface beneath comes more prominently into view; but this diminishes gradually till the eruption disappears, leaving oftentimes no trace of its former presence behind. It may leave, however, pigmentary stains, the result of the congestion. It is in the disappearance clears, and the ringed form or psoriasis, circinata, or the lepra of old authors is produced.
Etiology.-We possess no certain knowledge as to either the proximate or remote causes of the disease. It is not uncommon to find an extensive eruption in those who otherwise appear to enjoy the most robust health; while, on the other hand, it may appear only during periods of temporary debility, as in women during pregnancy and lactation.. That the affection is constitutional and connected with similar conditions to those underlying eczema we have no doubt, and each year’s experience more strongly confirms this opinion. Some have claimed that the eruption is purely local or due to the presence of a parasite. Positive evidence of this is wanting. Others pretend that it is but a relic or syphilis handed down from a remote ancestor. This view also has little to support it.
Psoriasis is often hereditary. It attacks males more than females and is most common between the ages of fifteen and thirty. Persons of sanguineous temperament are most liable to the disease perhaps, and it is seen in persons of all classes of society, and mostly in summer and winter.]
Prognosis.-The disease is mostly difficult of cure and has a tendency to recur. The most obstinate cases are those of psoriasis nummularis of the back and buttocks, in which there is much elevation and thickening and deep redness; and psoriasis about the hands and feet.
Diagnosis.-In well-marked and typical cases there can not be the least difficulty in diagnosis, especially to any one who has already seen an example of the disease. Unfortunately, however, cases are not always typical; and we must learn to distinguish psoriasis from syphilis, eczema, and dermatitis exfoliativa. As we have already stated, eczema may closely resemble psoriasis. In like manner the latter disease may closely counterfeit the former in its outward appearance; and in this particular case the diagnosis will be by no means easy, nor arrived at a glance, but only by careful consideration of the case in all its bearings. A squamous syphilide may closely resemble psoriasis; but here the history will aid us greatly if we bear in mind a few fundamental facts. In psoriatic cases of long standing we will have the history of repeated outbreaks of eruption, but they will all have presented the same general type- that is to say, a repetition of the same kind of eruption- a squamous syphilide will probably have been preceded by other eruptive attacks; but these have been in all probability a different sort of eruption-papular, pustular, or what not. Syphilis rarely repeats itself in its manifestations. If in addition we learn from the patient the prior existence of the primary lesion, or if we find other co- existing lesions, as alopecia, mucous patches, throat trouble, etc., we should not long remain in doubt as to the nature of the eruption about which we have been consulted. The existence of squamous lesions on the palms and soles in connection with squamous patches on the general surface is evidence positive of syphilis. In psoriasis the epidermic proliferation or desquamation is much greater than in syphilis. We have known a case of exfoliative dermatitis to be mistaken for psoriasis; but if we recollect that the characteristic feature of the former disease is the exfoliation of quite extensive laminae, of not very greatly thickened epidermis, sometimes several square inches in extent, there is no excuse for mistaking the one disease for the other.
