Current perception threshold in subacute myelo-optico-neuropathy.

We report the first current perception threshold (CPT) examination of sensory disturbance in subacute myelo-optico-neuropathy (SMON). SMON patients experience serious neurological symptoms, including dysesthesia, sensory loss, motor weakness, and visual impairment. During CPT examination, 5 Hz, 250 Hz, and 2,000 Hz stimulations were used to stimulate C fibers, A-delta fibers, and A-beta fibers, respectively. Ten SMON patients (mean age, 73.8 +/- 8.4 years) and ten age-matched controls (72.3 +/- 6.3 years) were studied using CPT measured at the index finger and near the external malleolus. The CPTs to 250 Hz and 2,000 Hz stimulations near the external malleolus were significantly higher and the CPT to 5 Hz stimulation was significantly lower in the SMON group than in the control group. Although peripheral nerve impairment is mild in SMON, pathological examination shows a decrease of large fibers. This is thought to increase the CPTs to 250 Hz and 2,000 Hz stimulations. The center of the gate control of pain exists in the posterior horn receiving information from the dorsal root ganglion. The dorsal root ganglion at the lumber cord is strongly impaired in SMON; therefore, the gate control may not work effectively, and decreases CPT to 5 Hz stimulation.