Angular vestibulo ocular reflex loss with preserved saccular function in Machado-Joseph disease.

Area of Science:

• Neuroscience
• Ophthalmology
• Genetics

Background:

• Machado-Joseph Disease (MJD), also known as spinocerebellar ataxia type 3, is an autosomal dominant neurodegenerative disorder.
• Vestibular dysfunction is a common but often underdiagnosed feature of MJD, impacting patient quality of life.

Purpose of the Study:

• To comprehensively evaluate vestibular function in MJD patients.
• To determine if specific vestibular pathways are selectively affected in MJD.
• To explore potential neurophysiological biomarkers for MJD diagnosis.

Main Methods:

• 21 MJD patients and 19 healthy controls underwent neuro-otological evaluation.
• Video Head Impulse Test (vHIT) assessed vestibulo-ocular reflex (VOR) gain in all six semicircular canals.
• Suppression Head Impulse Test (SHIMP) evaluated horizontal VOR, and cervical Vestibular Evoked Myogenic Potentials (cVEMP) assessed saccular function.

Main Results:

• MJD patients showed significantly reduced VOR gain in all semicircular canals compared to controls (p < 0.001).
• Horizontal VOR gain on SHIMP was also significantly lower in MJD patients (p < 0.001).
• Saccular function, assessed by cVEMP, was preserved in MJD patients, with no significant differences in latency or amplitude compared to controls.

Conclusions:

• Impaired horizontal and vertical VOR with preserved saccular function is a distinctive feature of MJD.
• This pattern suggests selective degeneration of vestibular nuclei, primarily medial and superior.
• Horizontal VOR gain measured by vHIT shows potential as a neurophysiological biomarker for MJD.