Nystagmus after experimental cervical lesions

Equilibrium disturbances may occur after neck lesions such as whiplash injuries. Abnormal proprioceptive inputs and vascular changes which involve not only the peripheral labyrinth, but also the brain stem are major factors producing these disturbances. Neck proprioceptor ablation was performed in healthy young adult squirrel monkeys by unilateral section of C1, C2 dorsal roots, or by injection of 1 cc of 1 percent Xylocaine® without epinephrine into the unilateral deep neck region. The dorsal root section was histologically confirmed by investigating spinal ganglion and adjacent nerve tissues. The Nauta stained spinal cord cross sections showed neuronal degeneration coming from the dorsal root. No spontaneous nystagmus was observed in the present series after section of the C1, C2 dorsal roots or Xylocaine® injection. After the Xylocaine® deep neck injection, the slow phase eye speed of optokinetic nystagmus declined in either direction in all animals. Slight decline of the quick component was also noticed. The wave form was also changed. The decline of slow phase eye speed partly represents the ablative effect of neck proprioceptors (joints, ligaments, and muscles), although the effect produced through other channels or by systemic toxicity cannot be eliminated. After the left C1, C2 dorsal root section, the slow phase eye speed declined only when there was clockwise stimulation. Statistical studies suggested significant differences between pre‐ and postoperative status. This finding suggested that the cervical input is connected to the oculo‐oculomotor pathway. Immediately after left C1, C2 dorsal root section, a reduction of the slow phase eye speed of postrotatory nystagmus occurred after counter‐clockwise rotation. The randomization test was used, and it was found that the postoperative scores are significantly lower than the pre‐operative scores. After the ablation of C1, C2 dorsal root, subjects failed to demonstrate any significant change in the pattern or numbers of pendular rotation nystagmic responses. On the other hand, three monkeys after Xylocaine® deep neck injection showed some change. The present experimental results indicate that the slow phase eye speed is a proper nystagmic parameter to study the neck proprioceptor contribution to oculomotor function. All animals after unilateral C1, C2 dorsal root section in the present series demonstrated moderate dysequilibrium (measured by the squirrel monkey rail test) confirming that neck injury can produce ataxia. There was no clear postoperative directional dominance of falls. For the diagnosis or investigation of the prognosis of many cervical disorders, bodily equilibrium examination is also important in addition to studying oculomotor function.