We assumed that changes in the excitability of motor nerves play some role in the stiffness of the neck, shoulders, and extremities in patients with vertigo. To obtain a better understanding of this phenomenon, we stimulated the receptors involved in body equilibrium with external stimuli, i.e., 1) caloric stimulation of the semicircular canals and 2) neck movements, and investigated changes in the F wave and the surface electromyogram (S-EMG) of the posterior cervical region.
The subjects were 40 healthy adults. Caloric stimulation of the semicircular canals was performed by infusing15°C water, and changes in the F wave examined. In addition, changes in the S-EMG by stimulation at temperatures of 5°C or 44°C were investigated. We examined changes in the F wave by the neck movements in association with theresults of the blindfold ed vertical writing test. The F wave of a patient with vertigo was also examined.
During vertigo induced by caloric stimulation of the semicircular canals, the excitability of the F wave on both the stimulated and non-stimulated sides increased, the S-EMGs showed decreased excitability on both the stimulated and non-stimulated sides during maximum voluntary contraction in the subject who experienced severe vertigo, nystagmus, and nausea. The changes in the F wave induced by the neck movements were small. However, excitability increased more significantly during posterior flexion than during other movements, and the angle of deviation of the letters written blindly tended to deviate most markedly toward the left during posterior flexion. The F wave of the patient with vertigo showed excitability, but it tended to decrease as the vertigo diminished.
These findings suggest that vertigo is accompanied by changes in the excitability of motor nerves. These changes are somehow related to the muscle stiffening that results from vertigo.