Specific impairment of BAER's in Friedreich's ataxia. Auditory evoked responses in clinical evaluation and differential diagnosis.

We have investigated brainstem and cortical auditory responses (BAERs and CAERs) in 16 cases of Friedreich's ataxia (FA) and have compared the findings with those obtained in 2 cases of familial spastic paraplegia (FSP), in 5 cases of Charcot-Marie-Tooth disease (CMTD), and in 6 cases of atypical FA of uncertain classification. BAERs could not be elicited in 11 FA patients and constantly disappeared at a higher intensity threshold than in normal subjects in the remaining 5 patients. BAERs were normal or only slightly abnormal in FSP and CMTD patients. CAERs were normal in all 29 patients. BAERs tended to disappear with the progression of FA and BAER thresholds were correlated with the Inherited Ataxias Clinical Rating Scale score, which is an index of the severity of illness. BAERs contributed to the diagnosis, or exclusion of FA in patients with an atypical picture. It is suggested that in FA myelinated fibers in the spiral ganglion are partially affected, resulting in the decrease of wave amplitude such as occurs for peripheral sensory potentials.