Abnormal sympathetic hyper-reactivity in patients with myasthenia gravis: a prospective study

Patients with myasthenia gravis, especially those in crises, are not infrequently observed to demonstrate wide fluctuation in heart rate and blood pressure.

This study was conducted to assess autonomic function in patients with myasthenia gravis.

Patients with myasthenia gravis diagnosed on the basis of typical clinical details, edrophonium or neostigmine test, decremental response on repetitive nerve stimulation testing and anti acetyl choline receptor antibody testing, were compared with age and gender matched controls. Apart from detailed clinical evaluation, all subjects underwent tests of autonomic function, viz. heart rate and blood pressure response on orthostatic tests and isometric handgrip test, Valsalva maneuver, R-R interval variation (RRIV) and the sympathetic skin response (SSR). Results were compared with those in the control group using repeated measures ANOVA and the paired t-test.

Sixty-four patients (27 males, 37 females) with a mean age of 40.5 ± 17 years) with myasthenia gravis of an average 3 ± 4 years duration, and 241 normal controls were enrolled. On the orthostatic tests, patients showed rise in heart rate, systolic and diastolic blood pressure, as did controls, however, the rate and the duration of rise was significantly higher than in the controls (p < 0.01). Similar difference between patients and controls, in rate of rise of these parameters was observed on the isometric hand grip test. No significant difference was observed between the two groups on tests of parasympathetic function (Valsalva ratio, RRIV). These effects could also partially be due to pyridostigmine, which all patients were receiving.

This study suggests sympathetic hyper-reactivity in patients with myasthenia gravis, which could be responsible for serious hemodynamic instability in patients in crisis.