Abnormal auditory neural activity in individuals with spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive disorder characterized by hypotonia, progressive muscle weakness and atrophy caused by progressive loss of motor neurons in the spinal cord and lower cranial nerve nuclei. The disease has also been associated with sensory neuropathies affecting the visual, somatosensory and auditory pathways. This case-control study investigated auditory neural function and perceptual ability in children and young adults with SMA. Twenty individuals with genetically confirmed SMA of varying severity (Types 1-3) participated. Sixteen children/young adults aged 6-20 years and 16 age-, gender- and hearing-level matched controls underwent a battery of peripheral and central auditory assessments. These included sound detection measurement, otoacoustic emission and auditory brainstem response testing and speech perception evaluation. In addition, four infants (3-28 months) treated with disease-modifying therapies underwent auditory brainstem response assessment. Despite normal cochlear responses and normal sound detection, most child or young adult participants presented with clinically abnormal auditory neural function and significant speech perception deficits. Auditory brainstem response amplitudes were reduced and latencies increased relative to matched controls (P < 0.005) consistent with axonopathy and/or demyelination in the auditory brainstem. Furthermore, both monaural and binaural speech perception in noise were impaired (P < 0.01) suggesting the presence of significant neural distortion and spatial processing disruption. In contrast, evoked potential findings for our small group of pre-symptomatic infants were normal. The results of this study demonstrate that auditory neural and binaural processing deficits are common in children and young adults with SMA. As such, auditory assessment including auditory brainstem function and speech perception in background noise should be routinely carried out in this population. Interventions specifically designed to improve hearing in background noise (such as remote-microphone listening systems) should be considered to optimize speech/language and psychosocial development and academic outcomes in affected individuals.