STUDIES ON ITCHING : The Mechanism of Itching in an Itching Inflammatory Skin Lesion
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概要
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The authors interpretation of the mechanism of the development of an itch sensation is based first of all on the assumption that a cutaneous stimulation may alter the excitability of the local pain nerve fibers, raising or lowering it, and causing a pain or an itch sensation as a closely related subjective symptom, in response to its pattern and intensity.The assumption is derived from this fact: the development of skin inflammation is invariably attended with hyperalgesia and/or itching hyper-excitability, but not with tactile hyperesthesia Nor does it ever happen that ocular or auditory inflammation is attended with any optic or auditory hyperesthesia, though sight or hearing declines in hypoesthesia in some conditions, indicating that the nerve fibers conducting pain or itch impulses (pain fibers) may be different in the behavior of their excitability in inflammation from those carrying auditory, visual or tactile impulses. This implies, in other words, that pain fibers, even if not any other, of the skin may be made hyperexcitable in skin inflammation and also in response to some particular pattern of artificial stimulation.Such a rise in the excitability of cutaneous pain nerve fibers may be demonstrable in a skin inflamed area, as for instance, a tuberculin-caused inflammatory skin area, as has been described in the 3rd chapter.A theory advanced by Rothman (1) (2) -the most reliable of the theories so far set forth on the mechanism of itching in an itching skin lesion-seems to be based on the mechanism of experimentally induced itching : this theory, if carefully read, will be taken to imply that itching resulting f roan an inflammatory skin lesion is identical in its mechanism with experimentally induced itching such as caused by histamine given intradermally or caused by C<SUB>2</SUB>O snow applied to a skin area .However, a further investigation seems to be necessary before the problem, whether or not the mechanism of itching in an inflamed skin area and that of experimentally induced itching are utterly the same, may be finally settled. On this account, itching in an inflamed skin lesion may well be distinguished provisionally from experimentally induced itching in considering the mechanism of its development.The mechanism of itching resulting from an inflammatory skin lesion such as eczema or dermatitis (urticaria excluded) could be interpreted as follows : with the onset of inflammation an inflammatory skin area is automatically placed in a state of hypersensitivity, the local nerve fibers (pain fibers) becoming automatically enhanced in their excitability to stimuli ; subjective symptoms such as itching, itching pain or pain may develop when the local nerve fibers (pain fibers) in a hyperexcitable state are stimulated from the inside or the outside of an inflammatory lesion ; the subjective symptoms thus produced are felt as itch or pain in response to the strength of the stimuli ; the subjective symptoms are felt often as itching and rarely as pain, because the nerve fibers are stimulated mildly in the majority of cases. See the enclosed paper for proper reference form.
- 久留米大学医学部 The Kurume Medical Journal 編集部の論文