PSORIASIS.
Definition.—Psoriasis is a cutaneous disease characterized by the presence of silvery-white perfectly-dry scales, which overlie a reddish, shining base.
Symptoms.—The eruption of psoriasis is always dry and scaly. It begins in one or more red points, which quickly be come covered with white, silvery scales. These may be readily scratched off by the finger-nail, and when this is done a bleeding surface is exposed. When many of these small, scaly lesions are present, the eruption is described as punctate psoriasis, and this form of the eruption is comparatively more frequent in children than in adults; when the scaly lesions increase in size and appear like drops of grease or thin mortar spat tered over the skin, we have the guttate form of the disease; and when the patches assume the size and shape of silver coins they are often described as nummular psoriasis. By healing in the centre these lesions may be converted into scaly rings, or by peripheral in crease and coalescence they may result in the formation of extensive scaly patches. Though the disease is not un commonly met in children, diffused or general psoriasis is rarely met with among them. It is not generally so well developed and so extensive as it is apt to be in later years. The amount of scaliness present in any case depends upon the attention which the patient naturally devotes to his skin. As the eruption tends to disappear, the scaling grows less, often disappearing from the centre of the patch and leaving a mar ginate ring. Finally the redness fades and the skin assumes a normal appear ance, except in certain cases, where pigmentation may occur. In rare cases of psoriasis the eruption may tend to rapidly involve the whole skin. The cutaneous congestion is severe, and large flakes of partly-detached epidermis may take the place of the silvery scales.
Psoriasis is usually seen upon the ex tensor surface of the extremities, and is especially apt to be noted about the el bows and knees. When upon the scalp
the scaly patches are apt to be small, numerous, and circular, with healthy skin intervening. The eruption upon one extremity or on one side of the trunk is usually duplicated upon the other side (George Henry Fox).
Pruritus may or may not be com plained of, and the patients may be in apparently good health. Disorders of the muscles and joints are often noted, however.
Diagnosis.—Diagnosis of psoriasis, as a rule, presents no difficulties; the sil very-white, perfectly-dry scales are alto gether characteristic. Upon the scalp it may be confounded with seborrhoea, but the absence of inflammatory redden ing and the greasy character of the scales in the latter affection will serve to dis tinguish it from the former. (Hartzell.) ECZEMA.—Whether occurring in small disks or in large, irregular patches, the border in psoriasis is always sharply de fined, and never shades off gradually into the surrounding healthy skin, as does the ordinary patch of eczema. This is a diagnostic point of great importance. In many cases of eczema the patches may be dry and scaly and present a re semblance to those of psoriasis, but the rounded, silvery disks or larger margi nate patches of the latter disease are usually so characteristic that an error in diagnosis is not likely to be made. While eczema may appear upon almost any part of the body, and often exhibits a tendency to attack the flexor aspect of the joints and other parts where the skin is thin and delicate, psoriasis, as stated, is generally seen upon the extensor sur face of the extremities, and is especially apt to be noted about the elbows and knees. (George Henry Fox.)