POLARIZATION OPTICAL STUDIES OF HYPERKERATOSIS,

Previous polarization optical studies of adult and embryonic human epidermis have been devoted to the elucidation of the morphology of its fibrous structure. In unstained vertical sections of human abdominal skin, the most intense double refraction occurs in the stratum corneum and stratum lucidum. In these layers birefringent material is oriented parallel to the surface plane; below this region the birefringent fibres are oriented perpendicularly to the surface (1). Similar observations have been made by other authors (2, 3), among them Mercer, who has compared the appearance of the epidermis under the polarization and electron microscopes. He noted that the fibrils (tonofibrils) in the lower layers of the epidermis were weakly birefringent. At the level of the appearance of keratohyalin there was a sudden rise in birefringenee associated with a change in orientation of the fibres from a vertical to a horizontal direction. In tissue cultures of stripped epidermis, Matoltsy has shown that in 3 to 5 days' old explants the originally vertically oriented birefringent material becomes reoriented in a plane parallel to the surface (4). On the 7th day, a definite keratogenous zone became visible, while all the birefringent epidermal fibres were still oriented parallel to the skin surface. The significance of these findings will be discussed later. Studies of the development of the birefringent fibrillar system of the human epidermis have yet to be carried out, but similar observations of the chick embryo have been made (5) and it has been shown that around the 16th day of embryonic life the periderm or epitrichium reveals a very weak birefringenee. However, moderate birefringence appears during the next 2 days of embryonic life when the true cornified layer is formed. Between the 18th and 21st days of embryonic * From the Department of Pathology, Memorial Hospital, Wilmington, Delaware. This study was supported by a grant from the Permanent Science Fund of the American Academy of Arts and Sciences. Presented at the Twentieth Annual Meeting of The Society for Investigative Dermatology, Inc., Atlantic City, N. J., June 6, 1959. life, the epidermis reaches its final state; at this stage the eornified layer shows intense double refraction. It is of interest that in the chick embryo, the long axis of the cells of the periderm and of the embryonic horny layer is parallel to the skin surface and the early keratin fibres are also oriented in the same plane. There is only one polarization optical study of pathologic epidermis. Nieuwmeijer examined the tonofibrils in bullous dermatoses by this method and found differences between the tonofibrillar systems in pemphigus and dermatitis herpetiformis (6). In pemphigus, in the areas of acantholysis, the tonofibrils were greatly decreased, whereas in dermatitis herpetiformis the tonofibrils were pushed aside by the fluid in the bullae. Recently, I used polarization optical methods to investigate the anomaly of keratin formation in psoriasis (7). It was found that the birefringent tonofibrillar system persisted throughout the psoriatic epidermis and in the parakeratotic scale, but the mature keratin fibres failed to develop into a coherent horny layer. These changes were reflected in the psoriatic nail (8) where immature keratinization was evident from the extensive parakeratosis combined with persistence of a low degree of double refraction in much of the fibrous structure of the nail plate and in the adherent hyponychium. These abnormalities were associated with alterations in the non-fibrous components of the nail and epidermis, manifested histochemically by cytoplasmie metachromasia in the parakeratotie cells and by an increased uptake of the Gram stain in the affected areas. In the present work the defects in the fibrous structure of the epidermis were investigated in conditions characterized by the formation of anomalous horny layers.