Asymmetrical Auditory Dysfunction as a Potential Nonmotor Lateralizing Sign in Parkinson's Disease: A Case-Control Study.

Introduction: Parkinson's disease (PD) is a complex neurodegenerative disorder that often presents with unilateral motor symptoms at the onset. While motor symptoms such as tremor, bradykinesia, rigidity, and postural instability are the signs of PD, nonmotor symptoms also significantly impact the patient's quality of life. One such nonmotor symptom is auditory dysfunction, which has been increasingly recognized as a feature of PD.

Objectives: Our purpose is to evaluate auditory impairment in PD patients and its asymmetry as a biomarker to differentiate PD from other neurodegenerative disorders that do not exhibit this lateralized auditory dysfunction.

Subjects and methodology: Our study included 60 patients with parkinsonism "the study group", and 40 healthy individuals "the control group." All participants underwent three auditory tests: pure tone audiometry (PTA), auditory brainstem response (ABR), and otoacoustic emissions (OAE).

Results: PTA thresholds were significantly higher in the PD group, especially on the affected side. ABR absolute latencies and interpeak latencies were significantly delayed in PD, with the delays being more pronounced on the affected side. The distortion product OAEs showed a significant decrease in amplitude on the affected side compared to the nonaffected side. Furthermore, its amplitude was highly significantly reduced when compared to the control group.

Conclusion: The asymmetry of the audiological responses in PD patients could be a valuable nonmotor marker of PD, enhancing our understanding of its broader impact on sensory systems and aiding in more precise diagnosis and monitoring of the disease.