Effective Myasthenia Gravis Diagnosis With the Edrophonium Test

The edrophonium test was found to be both effective in diagnosing patients with myasthenia gravis (MG) with high specificity and sensitivity, according to a study published in Neurological Research and Practice.¹ The study found that the test was less likely to give positive test results in certain subgroups of MG, and adverse events were less common.

MG is an autoimmune disorder that primarily affects the muscles in the body, most commonly in the face, neck, and limbs.² The condition is often caused by autoantibodies against the postsynaptic acetylcholine receptor (AChR) but can also be caused by antibodies against the muscle-specific kinase (MuSK) or low-density lipoprotein-related protein 4 (LRP4).¹ Tests for diagnosing MG include repetitive nerve stimulation (RNS) and single-fiber electromyography, but these are not always available to use, making the edrophonium test a valuable resource, even with its potential for adverse effects. This study aimed to assess how well the edrophonium test performs in diagnosing patients with MG.

This was a retrospective study, with data collected from the Department of Neurology of the Medical University of Vienna. All data came from the period between January 1991 and January 2024, with all clinical, diagnostic, and demographic data extracted. A positive antibody test or positivity for antibodies along with typical clinical symptoms was used to diagnose MG. Patients who had symptoms of MG with a seronegative result were included if there was a response to treatment or there was a reduction in symptoms after RNS. The control group was made up of patients where a different diagnosis was suspected and patients who did not have AChR antibodies where MG was not the cause.

The edrophonium test involved an intravenous treatment of 2 mg of edrophonium chloride before a second intravenous dose of 8 mg was administered 60 seconds later as long as the patient showed no adverse effects. Neurologists graded the positive responses at the time of diagnosis but were dichotomized to moderate/strong vs minimal for this analysis.

There were 182 patients with MG included in this study along with 324 controls. A total of 41.2% of the participants were women in the MG group vs 55.2% in the control group. The mean (SD) age was 55.8 (19.3) years and 53.6 (16.9) years, respectively. There were 6 patients with antibodies against MuSK and 1 patient that was positive for LRP4 antibodies.

The edrophonium test had a specificity of 87.7% and a sensitivity of 83.5% in the whole group. There were no significant differences found in the sensitivity between patients with AchR-MG, MuSK-MG, early onset AChR-MG, or late onset AChR-MG. A clinical response was found in 86.3% of the 51 patients with generalized MG who were only tested for ocular symptoms, and 81.8% of the 22 patients tested for bulbar or limb weakness had a positive test result.

Patients with a decrement after RNS had a higher sensitivity for the test compared with patients without a decrement (88.4% vs 66.7%). There was no decrement found in 12 of the 34 patients with MG who had a negative test. A strong response to the test was found in a higher percentage of those with MG compared with the control (78.3% vs 50.0%).

Patients with MG who had a positive RNS result had increased odds for a clinical response to edrophonium (OR, 3.79; 95% CI, 1.48-10.33). Lower odds of a positive test were associated with the presence of antibodies against MuSK compared with AChR (OR, 0.08; 95% CI, 0.01-0.82). A total of 11.5% of the entire cohort reported an adverse event, with 91.4% of the cohort having only a mild adverse event. Only 1 patient reported a severe adverse event. Vertigo, muscle cramping, lacrimation, nausea, and hyperhidrosis were the most common adverse events.

There were some limitations to this study, notably that a retrospective design to the study could have introduced information bias. Only ocular symptoms were tested in most of the patients diagnosed with generalized MG, which could have introduced selection bias. Test results could have been influenced by observer bias and variability between the different neurologists evaluating the results. The instability of the effect estimate for antibody status was a limit of the logistic regression model.

The authors concluded that they “provide robust real-world evidence for the diagnostic performance and safety of the edrophonium test in a large and heterogeneous cohort of patients with [MG].” In particular, edrophonium tests can be used for testing for ocular MG, which is easier to detect when using this test compared with RNS.

References

1. Keritam O, Kräutler JB, Gharib D, et al. Diagnostic performance and safety of the edrophonium test in myasthenia gravis: a retrospective case-control study. Neurol Res Pract. 2026;8:11. doi:10.1186/s42466-026-00468-6
2. Myasthenia gravis. Cleveland Clinic. Updated November 10, 2023. Accessed February 10, 2026. https://my.clevelandclinic.org/health/diseases/17252-myasthenia-gravis-mg