DERMOGRAPHISM (grech, derma skin + grapho to write, represent) — decolourization of skin at her mechanical irritation.
To cause local D., on skin carry out by a blunt end of a stick to dia. 2 — 3 mm. Usually in 8 — 20 sec., sometimes a bit later, the white strip — a white dermographism appears — length and width a cut precisely match the surface subjected to irritation (fig. 6). In 1 — 10 min. the strip disappears. This blanching of skin is connected with a spasm of capillaries.
During the carrying out on skin a blunt object with pressure big, than it is required for white D.'s receiving, usually arises are red y a dermographism (fig. 7). It appears in 5 — 15 sec. and can remain till two o'clock. The surface, on a cut develops red D., precisely corresponds to the area subjected to irritation. Reddening is caused by a trichangiectasia of the irritated area.
Thus, local D.'s emergence is connected with mechanical irritation of a wall of capillaries: the weak irritation gives a spasm of capillaries, i.e. white D., stronger — a trichangiectasia, i.e. red.
During the carrying out on skin a blunt object with considerable pressure the sublime dermographism appears — at first it is formed red, and in 1 — 2 min. — the white sublime strip (fig. 8) surrounded with a deckle-edged bright red zone. Formation of an eminence, i.e. hypostasis, apparently, is connected with allocation by cells of epidermis which are exposed to traumatization, mediators increasing permeability of a wall of capillaries. Sublime D. is also local reaction to excitement of elements of a capillary wall. Some persons at similar irritation have an urtikarny dermographism (in the form of blisters) caused by substantial increase of permeability of a vascular wall.
The reflex dermographism (fig. 9) appears during the carrying out on skin of the line an edge of a needle. In 5 — 30 sec. the strip 1 — 6 mm wide and more deckle-edged, consisting of bright red spots is formed, between to-rymi sites of skin of normal coloring or more pale, than normal lie. Reaction period fluctuates in wide limits (up to 10 min.).
Erubescence at reflex D. — result of expansion of arterioles, but not capillaries, is a typical vasomotor reflex. At the centers of defeat in a spinal cord reflex D. in one cases drops out only in the dermatomas connected with the destroyed segments of a spinal cord through which there passes the spinal arch of this reflex. In other cases, at a break of a spinal cord, reflex D. drops out in the dermatomas connected with the segments lying both at the level of the center and below it. It means that reflex D.'s arch becomes isolated not only on spinal, but also at the cerebral levels.
Studying of various forms D. has diagnostic value. Reflex D.'s loss in the dermatomas innervated only by the struck segments of a spinal cord gives the chance to establish top and bottom borders of the center. Its loss in the dermatomas innervated as the struck segments, and underlying indicates only the upper bound of the center. Results of studying of local D. can promote clarification of a functional condition of capillaries of skin. However at the same time it must be kept in mind that reactivity of capillaries of skin is defined by a number of external factors — temperature of skin, the environment, etc. Therefore it is possible to attach significance only to sharp disturbances of local D. — loss or its considerable strengthening. D.'s loss is observed at exhaustion of an organism, heavy intoxications of a nervous system and so forth. Local D.'s strengthening develops at some functional and organic diseases of a nervous system, napr, meningitis, at patients with vegetative neurosis, at a bazedovy disease and so forth. It is supposed that narrowing of capillaries is activated by a sympathetic nervous system, and their expansion and strengthening of transudation — parasympathetic. Therefore sharp strengthening of white D. can indicate to some extent dominance of a sympathetic innervation, and red and sublime D.'s strengthening — dominance parasympathetic. However D. cannot serve as an indicator of a condition of vessels of other parts of a body, except skin (see).
Bibliography: The multivolume guide to neurology, under the editorship of S. N. Davidenkov, t. 2, page 331, M., 1962, bibliogr.; P at-setsky I. I. Vegetative nervous disturbances, M., 1958, bibliogr.; M about p-rad-Krohn G. H. The clinical examination of the nervous system, L., 1964.
A. M. Grinstein.