Relative preservation of lumbrical versus thenar motor fibres in neurogenic disorders.

At late stages of median nerve entrapment in the carpal tunnel there may be total denervation of the thenar muscles. Surface electrodes over the thenar endplate zone may record an initial and predominantly positive "M" response to supramaximal median nerve stimulation. By a combination of techniques, it has been established that this surface positive response originates from surviving lumbrical muscles innervated by the median nerve. Their …