Skeletal muscle abnormalities associated with occupational exposure to mercury vapours

There is scarce information on the possible effects of chronic exposure to mercury on skeletal muscle. Dental personnel are frequently exposed to inha lation of metallic mercury vapours. The skeletal muscle of five technicians and one dentist (females, age 36-55) was studied. All of them presented sy mptoms of chronic mercury poisoning. Needle biopsy was taken from the quadr iceps femoris muscle and samples were prepared for light microscope histoch emistry and for transmission electron microscopy. Selective atrophy of type IIB muscle fibres was found in patients, and in one of them there was fibr e grouping. Most of the muscles showed increased fibre area per capillary. Atrophy was confirmed by the ultrastructural study, demonstrating increase of intermyofibrillar spaces, loss of myofibrils or complete disappearance i n some fibres, and sarcolemmal foldings. Splitting of the fibres was also f ound. Some capillaries were altered, showing endothelial infoldings into th e lumen, thickened basement membrane and partial or total occlusion. The al terations found in muscle may be secondary to nerve damage, to ischemia cau sed by capillary lesion and/or to a direct effect of mercury on muscle fibr e proteins.