Are motoneurons involved in muscular dystrophy?

In the early seventies, a suggestion that even in muscular dystrophy a neur ogenic factor may be involved, was formulated. The argument which followed this suggestion, resulted in eventual abandoning of this concept even by it s author. This discussion however has never been supported by any systemati c study of motoneuron activity in muscular dystrophy. We examined an activi ty of motoneurons supplying brachial biceps in eight controls and 26 patien ts affected by Duchenne muscular dystrophy by studying single motor unit (M U) potentials picked up by fine wire bipolar electrodes. In the majority of patients, MU firing rates were higher as compared to controls and increase d more rapidly with increasing force level. The relationship between standa rd deviation of interspike intervals and their mean value, SD((x) over bar) , was shifted towards the shorter intervals and lower SDs. The numerical va lues describing these changes were correlated with severity of the disease. There is evidence that the break-point of the function SD((x) over bar) is correlated with motoneuron properties, in particular with after-hyperpolar ization duration. In muscular dystrophy, this break-point corresponds to th e shorter interspike intervals. We suggest that the motoneurons in muscular dystrophy are altered either in response to the muscle degeneration, or as a result of the disease itself. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.