Saccadic eye movements in myasthenia gravis

Area of Science:

• Ophthalmology
• Neurology
• Neuroscience

Background:

• Myasthenia gravis (MG) can cause ophthalmoplegia, potentially mimicking other neurological conditions affecting eye movements.
• Differentiating MG from other causes of ophthalmoplegia is crucial for accurate diagnosis and treatment.
• Saccadic velocity measurement is a potential tool for distinguishing between different etiologies of eye movement disorders.

Purpose of the Study:

• To evaluate the utility of peak horizontal saccadic velocities in differentiating myasthenia gravis (MG) from other causes of ophthalmoplegia.
• To compare saccadic velocities in MG patients with those in patients with sixth cranial nerve palsy (CNP) and chronic progressive external ophthalmoplegia (PEO), as well as normal subjects.

Main Methods:

• Horizontal eye movements were recorded using electrooculography (EOG) or infrared scleral reflection (IR).
• Peak saccadic velocities were measured in 42 MG patients, 26 CNP patients, 19 PEO patients, and 28 normal subjects for saccade amplitudes of 10, 20, and 30 degrees.
• Analysis included comparing group means and identifying outliers (velocities outside the normal range).

Main Results:

• With IR, mean saccadic velocities for 10-degree saccades were similar between MG patients and normal subjects.
• With EOG, MG patients showed statistically significant, though small, decreases in mean velocities for 10, 20, and 30-degree saccades compared to normal subjects.
• A notable percentage of MG patients (21-28%) had saccadic velocities outside the normal range.
• In contrast, CNP and PEO patients exhibited markedly lower mean saccadic velocities than MG and normal subjects, with high frequencies of outliers (89-100% for CNP, 88-100% for PEO).

Conclusions:

• Peak horizontal saccadic velocity measurements, particularly using EOG, can aid in differentiating myasthenia gravis from other causes of ophthalmoplegia.
• The distinct patterns of saccadic velocity abnormalities in CNP and PEO compared to MG support the diagnostic value of this measurement.
• Saccadic velocity analysis offers a valuable, objective method for differential diagnosis in ophthalmoplegia.