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Behavior Response to Sounds and Auditory Brainstem Response (ABR) in Children with Mental Retardation

Mentally retarded children often appear as if they had severe hearing impairment without peripheral deafness. In relation to this clinical observation, the present study was conducted to determine; 1) the relation between the developmental quotient (DQ) and the threshold of conventional audiometry, and 2) the relation between DQ and the presence of brainstem lesions detected by auditory brainstem response (ABR). Eighty-eight mentally retarded children (one to five years old) were studied. Patients who showed neurological abnormal signs other than mental retardation were excluded. As the control, thirty age-matched normal children and ten normal adults were studied. DQ was evaluated by the Tsumori and Inage’s Developmental Assessment for Infants and Children. Conditioned orientation reflex audiometry (COR) was carried out according to the method by Suzuki. Since the thresholds of ABR were within a normal range in all the patients studied, they were considered to have no abnormality in peripheral hearing acuity. The degree of DQ inversely correlated with the difference in the threshold between COR and ABR (COR-ABR). Because COR-ABR is regarded to indicate the apparent hearing impairment, this finding was considered to support the above-mentioned clinical observation. The latency of waves I and V were measured and the brainstem conduction time was expressed by V-I interval. Prolonged latency of the waves or prolongation of V-I interval was found in 40.9% of the patients, but the difference of DQs was not significant between the patients with and without the abnormal brainstem condition. The prolongation of the latency of ABR suggests the presence of some brainstem lesions, although it does not mean definite anatomical lesions. All of the children investigated in this study did not have any clinical focal sign to suggest anatomical brainstem lesions. The abnormalities of ABR observed in the mentally retarded children are probably due to the developmental delay or immaturity of the brainstem. (Acta Paediatr Sep. 24(3):391 1982)