Special sensory ataxia in Miller Fisher syndrome detected by postural body sway analysis.

To investigate whether ataxia in Miller Fisher syndrome (MFS) is caused by loss of proprioception or cerebellar dysfunction, we studied the power spectrum peak of the body sway frequency in 10 MFS patients, and compared the results with those of patients with cerebellar or sensory ataxia. The cerebellar patients had a peak at 2.4 Hz, whereas sensory ataxia patients had a 1-Hz peak. Nine of the MFS patients had a distinct 1-Hz peak. Clinical sensory loss or abnormal sensory nerve potentials were present in only 3 patients, whereas soleus H-reflexes were absent in all the MFS patients. MFS patients have dysfunction of the proprioceptive afferent system, and the special sensory ataxia may be caused by the selective involvement of muscle spindle afferents.