Auditory and vestibular function in mitochondrial patients harbouring the m.3243A>G variant

Hearing impairment is a frequent clinical feature in patients with mitochondrial disease harbouring the pathogenic variant, m.3243A>G. However, auditory neural dysfunction, its perceptual consequences and implications for patient management are not established. Similarly, the association with vestibular impairment has not yet been explored. This case-control study investigated in 12 adults with genetically confirmed m.3243A>G adults [9 females; 45.5 ± 16.3 years (range 18-66); 47.1 ± 21.5 hearing level, dB] compared with 12 age, sex and hearing level-matched controls with sensory (cochlear level) hearing loss [9 females; 46.6 ± 11.8 years (range 23-59); 47.7 ± 25.4 hearing level, dB]. Participants underwent a battery of electroacoustic, electrophysiologic and perceptual tests, which included pure tone audiometry, otoacoustic emissions, auditory brainstem responses, auditory temporal processing measures, monaural/binaural speech perception, balance and vestibular testing and self-reported questionnaires (dizziness and hearing disability). Our findings showed evidence of auditory neural abnormality and perceptual deficits greater than expected for cochlear pathology. Compared with matched controls with sensory hearing loss, adults with mitochondrial disease harbouring m.3243A>G had abnormal electrophysiologic responses from the VIII nerve and auditory brainstem (P = 0.005), an impaired capacity to encode rapidly occurring acoustic signal changes (P = 0.005), a reduced ability to localize sound sources (P = 0.028) and impaired speech perception in background noise (P = 0.008). Additionally, vestibular dysfunction (P = 0.011), greater perceived dizziness (P = 0.001) and reduced stance time (balance, P = 0.009) were also seen in participants with m.3243A>G mitochondrial disease when compared with matched counterparts. This pilot study revealed that auditory evaluation including evoked potential responses from the auditory nerve/brainstem and speech perception in noise tests should form an important part of the management for individuals with m.3243A>G-related mitochondrial disease. Those presenting with hearing impairment and symptoms concerning balance and dizziness should undergo vestibular testing and appropriate management.