Otoneurological findings in Friedreich's ataxia and other inherited neuropathies.

Fifteen cases of Friedreich's ataxia (FA) were examined using an otoneurological test battery that included tone and speech audiometry, the synthetic sentence identification (SSI) test, impedance audiometry, cortical auditory-evoked response (CAER), brainstem auditory-evoked response (ABR) and electronystagmography. We also obtained ABR and CAER findings in 2 cases of familial spastic paraplegia, in 5 cases of Charcot-Marie-Tooth disease and 6 in cases of atypical FA of uncertain classification. The results of puretone and impedance audiometry were normal in all cases. ABR could not be elicited in 11 FA patients and were abnormal at higher intensity levels in the remaining 4 patients. In these 4 cases, however, the latencies were normal. ABR did not show any marked abnormalities in patients with familial spastic paraplegia or Charcot-Marie-Tooth disease. CAERs were normal in all 28 patients. ABRs tended to be absent with the progression of FA. ABR thresholds were correlated with the Inherited Ataxias Clinical Rating Scale score, which is an index of the severity of the illness. ABRs contributed to the diagnosis or to excluding FA in patients with an atypical clinical picture. The absence of ABRs and the normal latencies of the waves, when evoked, agree with the pathological finding of a reduction of fibers in the spinal root ganglion. SSI abnormalities and vestibular findings agree with this hypothesis.