Fiber-Specific Changes in White Matter Microstructure in Individuals With X-Linked Auditory Neuropathy

Area of Science:

• Neuroscience
• Audiology
• Medical Imaging

Background:

• Auditory neuropathy (AN) is a hearing disorder characterized by abnormal auditory nerve function.
• Determining the precise site of lesion and extent of dysfunction in AN remains challenging.
• X-linked AN is a specific form of this condition requiring further investigation into its underlying pathology.

Purpose of the Study:

• To investigate axonal degeneration in the brainstem white matter tracts of individuals with X-linked AN.
• To hypothesize that X-linked AN involves focal degeneration in the VIII nerve and/or auditory brainstem tracts.
• To correlate the degree of degeneration with auditory perceptual impairment.

Main Methods:

• Employed higher-order diffusion magnetic resonance imaging (dMRI) to quantify apparent fiber density.
• Utilized single-shell 3-tissue constrained spherical deconvolution and fixel-based analysis.
• Assessed 11 subjects with X-linked AN and 11 controls using behavioral and objective auditory measures.

Main Results:

• Fixel-based analysis revealed significantly lower apparent fiber density in the VIII nerve of X-linked AN subjects, indicating axonal degeneration.
• Auditory brainstem tracts also showed significant degeneration.
• Degeneration correlated with impaired temporal processing and poorer auditory assessments (sound detection, speech perception, binaural cues).

Conclusions:

• dMRI-derived apparent fiber density may aid in characterizing lesion site and dysfunction extent in AN.
• Quantifying degeneration can potentially guide future rehabilitation strategies for individuals with AN.
• VIII nerve dysfunction is a key feature of X-linked AN, while cochlear function is relatively preserved.