Enhancing the diagnostic yield of myasthenia gravis using 7-Hz repetitive nerve stimulation: an 11-year retrospective study.

OBJECTIVE

To investigate the diagnostic utility of augmenting the conventional 3-Hz repetitive nerve stimulation test (RNST) with a 7-Hz protocol in patients with myasthenia gravis (MG).

METHODS

We retrospectively analyzed 11 years of RNST data (2013-2023) from patients at a tertiary medical center. The diagnostic performance (sensitivity, specificity, positive predictive value [PPV], and negative predictive value [NPV]) of the conventional 3-Hz protocol was compared against a combined 3-Hz plus 7-Hz protocol.

RESULTS

Among 311 MG patients (208 generalized MG [gMG]; 103 ocular MG [oMG]), adding 7-Hz stimulation significantly improved the sensitivity for gMG from 69.0% to 82.1% without compromising specificity (91.7%). Multivariable regression confirmed that the combined protocol was independently associated with higher diagnostic yield in gMG (OR = 2.28, p = 0.019). Using a within-group paired analysis, 7-Hz RNST showed superior sensitivity compared to 3-Hz RNST. This increased diagnostic yield was predominantly observed in the gMG subgroup. Notably, 15% of MG patients were positive exclusively at 7 Hz, with the highest rescue rate observed in proximal muscles.

CONCLUSION

Incorporating 7-Hz RNST into standard diagnostic algorithms substantially enhances the detection of gMG, particularly when conventional 3-Hz testing yields negative results in proximal muscles.

SIGNIFICANCE: RNST protocol selection may be tailored by clinical phenotype to maximize sensitivity by adding 7 Hz RNST.