patches may be dry and scaly, and present a resemblance to those of psoriasis, but the rounded, silvery discs or larger marginate patches of the latter disease are usually so characteristic that an error in diagnosis is not likely to be made.
The localization of the eruption is another important diagnostic point. While eczema may appear upon almost any part of
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Fig. 14.—Guttate lesions with scales washed off.
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 is commonly seen upon the extensor surface of the extremities and is especially apt to be noted about the elbows and knees. Upon the scalp the two affections often present a strong resemblance, but in psoriasis the scaly patches
