LOCAL MYOPATHIC changes in muscle biopsies as a result of "needling" the muscle have been described and indicate that electromyogram or hypodermic needling must not be done in the site to be biopsied.1 We have found similar histological changes (ie, focal inflammatory myopathic changes) occurring after mild to moderate external trauma to guinea pig gastrocnemius muscles. The practical implication of this is that percussion with a reflex hammer or vigorous massage of a muscle to be biopsied may result in focal pathological changes which are not representative of the generalized musculature.
The gastrocnemius muscles of the left hind limbs of nine normal guinea pigs were traumatized manually by a variety of means. All but two of the animals underwent massage for ten seconds with a degree of pressure that would cause mild to moderate discomfort to a human thenar eminence but without lasting discomfort. In addition, these
Hathaway PW, Dahl DS, Engel WK. Myopathic Changes Produced by Local Trauma. Arch Neurol. 1969;21(4):355–357. doi:10.1001/archneur.1969.00480160027002
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