Elizabeth C. Jackson Esoda

CHEMICAL CHANGES IN PSORIATIC SCALES

Systematic chemical analysis of the horny layer is a relatively recent development in the study of psoriasis. This is somewhat surprising, especially if we consider that so many other organs and systems have been subjected to detailed investigation. One of the main reasons for these delayed studies seems to be the fact that the chemical composition of normal horny layers was also unknown and, therefore, no basis of comparison was available. It is due to the development of new techniques and to the painstaking spade work of a number of scientists1-13 that the time has finally arrived for the study of pathological horny layers. They are available in large quantities; an exfoliative case may produce several grams of scales daily. Their composition is remarkably constant. In our experience, washing1* and most of the topical therapeutic measures have no appreciable effect on the components we have studied. As a rule, scales can be obtained in reasonably pure form, free from admixture with other tissuesan important consideration in the case of a heterogeneous tissue like the skin. On the other hand, psoriatic epidermis is not available in unlimited quantities; even if it were, it is unlikely that the cellular layers could be separated from the highly uneven dermal papillae and the strongly adherent horny layer. Extensive chemical studies of the scales have been initiated by Gruneberg and Szakall.ls These authors were among the first to comment on the constancy of the chemical data. This constancy was in sharp contrast with such unpredictable and inconstant features of the disease as the composition of the serum proteins. The scales consistently reflect certain anomalies, even though the nature of the underlying disturbances is obscure. In these studies special attention has been paid to the essential role of the soluble components of the horny layer. I n contrast to hair or nail, which are built almost entirely of keratin, the horny layer consists of only about 60 or 70 per cent of water-insoluble horny framework; a large part of the remainder is soluble in water.3* These water-soluble compounds perform most of the essential protective functions of the skin surface. They maintain its pH, regulate the flow of water and bind moisture, protect against ultraviolet light, and help in detoxification.lB It is among these components that anomalies occur in psoriasis. Psoriatic scales offer many advantages for chemical studies.