Vestibular dysfunction: a frequent problem for adults with mitochondrial disease.

Mitochondrial diseases are a diverse group of genetic disorders caused by mutations in nuclear-encoded and mitochondrial DNA (mtDNA)-encoded genes. Disturbance in balance is common in adults with mitochondrial disease and usually attributed to an underlying peripheral neuropathy, skeletal myopathy and/or cerebellar disease, with limited treatment options. The vestibular system is central to balance control, and vestibular dysfunction causes vertigo, dizziness, oscillopsia, unsteadiness, and associated falls. Reports of vestibular dysfunction in mitochondrial disease are confined to small patient cohorts with limited and/or inconsistent use of neuro-otological assessments.1–3 Furthermore, despite the well-recognised association with hearing loss,2 the frequency and underlying pathophysiological basis of vestibular dysfunction in mitochondrial disease is currently unknown.We have undertaken a large-scale, cross-sectional cohort study investigating the prevalence, classification and predictors of vestibular dysfunction in adults with mitochondrial disease.All procedures were conducted as part of routine clinical care. The study was performed under the ethical guidelines issued by our institution, with written informed consent obtained from all participants for genetic studies. We included adults (aged 16 years or older) attending our specialist clinic between May 2016 and August 2017 with clinicopathologically and/or genetically confirmed mitochondrial disease and a suspected balance disorder. This cohort was subsequently evaluated by a specialist neuromuscular physiotherapist (SH) to exclude non-vestibular balance disorders. Patients with suspected vestibulopathy were subsequently referred for neuro-otological investigations (online supplementary table 1). Descriptive analyses were conducted on patient demographics, reported symptoms, neuro-otological and mitochondrial diagnoses, Newcastle Mitochondrial Disease Scale for Adults (NMDAS; a semiquantitative clinical rating scale for mitochondrial disease aimed at providing a validated and reproducible …