Measles rash. I. Light and electron microscopic study of skin eruptions.

Measles skin lesions were studied by light and electron microscopy. In the epidermis multinucleated giant cells were observed just beneath the hypertrophic horney layer at the maximum stage of rash; they were believed to result by an abnormal process of hyper- or parakeratosis. Neither typical inclusions nor viral nucleocapsids could be detected in any part of the epidermal layer. Most characteristical changes were dermal edema and spongiosis with mononuclear cell infiltration as well as the detection of measle virus-like microtubular structures (nucleocapsids) in the endothelium of dermal capillaries. Is is assumed that measles exanthema is a manifestation of an Arthus reaction elicited by viral antigen in the endothelium of dermal capillaries.