Abstract
Background The double crush hypothesis (DCH) that had been widely accepted seems to have been
dismissed recently. Prior to the DCH, retrograde changes in the proximal median nerve
in carpal tunnel syndrome (CTS) were reported. There has been no report of quantitative
analyzing about the effect of one site’s compression on another site all through the
same peripheral nerve in CTS patients.
Methods We measured the central motor conduction time (CMCT), motor conduction latency of
the cervical root region (CRL), peripheral path latency from the rootlet to the wrist
(PL) and motor distal latency (MDL) in the median nerve and ulnar nerves, respectively
in CTS patients.
Results MDL, PL and CRL were prolonged selectively in the median nerve, but not in the ulnar
nerve of CTS patients. And in the median nerve measurement, MDL was high (r = 0.59,
p < 0.0001) while PL showed a significant (r = -0.28, p < 0.05) relationship with
CRL. MDL was large (r = 0.58, p < 0.0001) and showed a close (r = 0.59, p < 0.0001)
relationship with the amplitude of CMAP. There was no significant difference between
the amplitude of the normal CRL group and that of the prolonged CRL group. This quantitative
analysis showed a linear relationship among MDL, CRL and CMAP amplitude.
Conclusion Dual entrapment lesions did not unexpectedly exaggerate the vulnerability or total
damage. The vulnerability and the damage were proportional to the severity of each
lesion. If the DCH term presented to an unexpectedly exaggerated degree, the cases
of double crush symdrome in the CTS patients were rare, but if the term DCH refers
to only this linear relationship, the DCH should not be dismissed.
