Oculomotor function in multiple system atrophy: clinical and laboratory features in 30 patients

Area of Science:

• Neurology
• Ophthalmology
• Neuroscience

Background:

• Differentiating multiple system atrophy (MSA) from idiopathic Parkinson's disease (PD) and atypical parkinsonism is clinically challenging.
• Oculomotor dysfunction is a key feature in neurodegenerative diseases, but its specific diagnostic utility in MSA requires further elucidation.

Purpose of the Study:

• To investigate the spectrum of clinical and laboratory oculomotor features in patients with probable multiple system atrophy (MSA).
• To identify specific oculomotor signs that can serve as diagnostic clues for MSA, particularly in differentiating it from other parkinsonian syndromes.

Main Methods:

• Clinical oculomotor examination of 30 patients with probable MSA (22 MSA-P, 8 MSA-C).
• Post-mortem examination in six patients to confirm MSA diagnosis.
• Detailed assessment of saccadic function, smooth pursuit, gaze-evoked nystagmus, and vestibulo-ocular reflex (VOR) suppression.

Main Results:

• Excessive square wave jerks (21/30), impaired smooth pursuit (28/30), and mild-moderate saccadic hypometria (22/30) were highly prevalent in MSA patients.
• Other notable findings included gaze-evoked nystagmus (12/30), positioning downbeat nystagmus (10/25), and reduced VOR suppression (16/24).
• Absence of these signs, particularly slow saccades or severe gaze restriction, suggested alternative diagnoses.

Conclusions:

• Oculomotor abnormalities such as excessive square wave jerks, saccadic hypometria, impaired VOR suppression, and specific nystagmus patterns are valuable "red flags" for diagnosing MSA.
• These findings aid in distinguishing MSA from idiopathic Parkinson's disease and other atypical parkinsonian disorders.
• Electro-oculography and caloric testing provided limited additional diagnostic value compared to detailed clinical examination.