Postauricular response in motor paresis with intracranial lesions.

The clinical usefulness of the postauricular response (PAR) in the evaluation of motor paresis was studied in 105 patients with intracranial lesions and 25 normal volunteers. Click stimuli at 90 dB hearing level were delivered in each ear, and PARs recorded from bilateral posterior auricular muscles with reference to the vertex (Cz). No volunteer demonstrated PAR in the relaxed posture, but in tensed postures increasing muscle tone PARs were elicited with a latency of 11.5 +/- 0.7 msec and an amplitude of 6.2 +/- 2.8 muV. Sixty-two patients (59%) had high-amplitude PARs in the relaxed posture. PARs were enhanced more frequently in paretic patients than in non-paretic patients (p less than 0.01). In subcortical lesions, the PAR latency had a significant correlation with the degree of motor paresis (p less than 0.005). In patients, the enhanced PAR amplitude suggested the presence of motor paresis associated with deep-seated mass lesions. The enhanced response is thought to be associated with dysfunction of the pyramidal and extrapyramidal tracts.