Muscular weakness in myasthenia gravis (MG) is commonly assessed using
Quantitative Myasthenia Gravis Score (QMG). More objective and quantitative
measures may complement the use of clinical scales and might detect
subclinical affection of muscles. We hypothesized that muscular weakness in
patients with MG can be quantified with the non-invasive Quantitative Motor
(Q-Motor) test for Grip Force Assessment (QGFA) and Involuntary Movement
Assessment (QIMA) and that pathological findings correlate with disease
severity as measured by QMG. Methods This was a cross-sectional pilot study
investigating patients with confirmed diagnosis of MG. Data was compared to
healthy controls (HC). Subjects were asked to lift a device (250 and 500 g)
equipped with electromagnetic sensors that measured grip force (GF) and three-
dimensional changes in position and orientation. These were used to calculate
the position index (PI) and orientation index (OI) as measures for involuntary
movements due to muscular weakness. Results Overall, 40 MG patients and 23 HC
were included. PI and OI were significantly higher in MG patients for both
weights in the dominant and non-dominant hand. Subgroup analysis revealed that
patients with clinically ocular myasthenia gravis (OMG) also showed
significantly higher values for PI and OI in both hands and for both weights.
Disease severity correlates with QIMA performance in the non-dominant hand.
Conclusion Q-Motor tests and particularly QIMA may be useful objective tools
for measuring motor impairment in MG and seem to detect subclinical
generalized motor signs in patients with OMG. Q-Motor parameters might serve
as sensitive endpoints for clinical trials in MG
