The pathologic changes in part reflect the rapid turnover of the epidermis, as well as inflammation. Normal turnover is one month. In psoriasis, turnover is as short as three days. Thus, the keratin differentiation process is impaired, there is a reduction in amount of high molecular weight keratin polypeptides, filaggrin and involucrin. Similar keratin changes are found in other skin diseases with rapid turnover including squamous cell cancer.
Lesions are often symmetrical, and located on the extremities, glans penis, and buccal mucosa.
In the latter they appear as white lacey areas. The Koebner phenomenon may be seen, as in psoriasis. This is a localized, cutaneous form of Lupus Erythematosus, with no associated systemic manifestations. These patients usually do not go on to develop systemic disease, however, many patients with SLE may exhibit lesions that are clinically and histologically indistiguishable from those of discoid lupus. The lesions may occur and worsen with sun exposure, so the use of sunscreens can reduce morbidity of this disease.