The intradermal mecholyl test for anidrosis; a diagnostic aid in leprosy

ABSTRACT

Sweat glands, though of sympathetic innervation, have acetylcholine as their chemical mediator, and normally they respond directly to that substance upon its injection. Metacholine (acetylbeta-methyl choline) or its chloride has the same effect on sweat glands as acetylcholine or its chloride. Removal or destruction of the post-ganglionic sympathetic nerves, resulting in denervation of the sweat glands, prevents them from responding to acetylcholine or metacholine. The reason for this is not known. It seems probable that one of the earliest consequences of tuberculoid leprosy in the skin is the denervation of sweat glands, and that this is an eventual consequence of leprosy of either type involving nerve trunks. The intradermal injection of metacholine chloride, therefore, frequently gives evidence of peripheral sympathetic nerve damage by showing loss of the normal sweat response. This manifestation may be interpreted as iniciative of leprosy in cases in which no equally cogent evidence to the contrary can be adduced, and may further be interpreted as indicative of nerve-damaging (i.e. tuberculoid) leprosy when it shows anidrosis which is coextensive with the visible skin lesion. Failure or marked diminution of the sweat response is frequently observed in facial lesions of so-called achromia parasitica, and occasionally in the normal skin of the face as well. The greatest advantage of the sweating test over the histamine test is that its results may be read with ease even in darkskinned patients.