The double crush syndrome.

Multilevel lesions along a peripheral nerve trunk do occur. In the double crush syndrome as postulated by Upton and McComas, the presence of a more proximal lesion does seem to render the more distal nerve trunk more vulnerable to compression. While the exact pathophysiologic mechanism of this interaction is not yet elucidated, it most likely relates to disturbances in axonal flow kinetics and the disruption of the neurofilament architecture. On a practical level our studies show that given a more proximal root compression less involvement of the median nerve across the carpal tunnel was required to produce symptoms. Furthermore, the surgical outcome of carpal tunnel release in this double crush group was poorer than in that group with isolated carpal tunnel involvement. It is important to preoperatively identify those patients who may have double crush lesions and thus anticipate a less than optimal result from surgical release of the peripheral nerve. Finally, when the double crush syndrome is present, both entrapments may require treatment for optimal results.