Digital vibrogram: a new diagnostic tool for sensory testing in compression neuropathy.

A Békésy audiometer was modified for use in analysis of vibrotactile sensibility of the hand at frequencies ranging from 8 to 500 Hz. In control subjects the "digital vibrogram" has a typical shape, which differs characteristically in patients with carpal tunnel syndrome (CTS). Changes in digital vibrogram usually parallel or precede abnormalities in neurophysiologic tests, and appear long before changes in two-point discrimination (2PD). One-hundred-thirty-two hands of 76 patients diagnosed as having CTS were tested with a vibrometer. Of 113 hands with normal 2PD, the digital vibrogram showed abnormal in 86 cases. Of 19 hands with abnormal 2PD, the digital vibrogram showed abnormal in all but three cases. Twenty-six hands with neurophysiologically normal appearance had abnormal digital vibrogram in 14 cases, while 53 hands neurophysiologically classified as CTS showed abnormal digital vibrogram in 44 cases. It is concluded that the digital vibrogram is a useful tool for early diagnosis of CTS.