Stimulated single-fiber electromyography in the diagnostic workup of diplopia and ptosis.

OBJECTIVE

Ptosis and diplopia are common neuro-ophthalmological presentations with a broad differential diagnosis. In clinical practice, stimulated single-fiber electromyography (SFEMG) is often requested when ocular myasthenia gravis (MG) remains a diagnostic consideration after initial evaluation. This study evaluated the diagnostic contribution of stimulated SFEMG in a real-world cohort of patients referred with ptosis and/or diplopia.

METHODS

Patients presenting with ptosis, diplopia or both were prospectively recruited and underwent comprehensive serological, radiological, and electrophysiological assessment, including SFEMG. Normative cut-offs for stimulated concentric needle SFEMG were established from 31 healthy controls and applied to the study population.

RESULTS

A total of 115 patients were included (diplopia n = 46, ptosis n = 25, both n = 44). MG was diagnosed in 46 patients. SFEMG showed a sensitivity of 60.9% (95% CI 0.45-0.75) and specificity of 92.8% (95% CI 0.84-0.98), with a positive predictive value of 84.9% and negative predictive value of 78.1%. SFEMG identified 7 seronegative MG cases and 16 cases with negative RNS. In the non-MG group (69/115), SFEMG was negative in 92.8%, supporting its role in excluding MG.

CONCLUSIONS

Stimulated SFEMG demonstrates high specificity in patients with ptosis and diplopia and is particularly useful in diagnostically challenging cases, including seronegative MG and RNS-negative patients.

SIGNIFICANCE: SFEMG represents a valuable second-line diagnostic tool in suspected ocular MG. Its high specificity supports its use in selected patients to confirm diagnosis and reduce the risk of MG overdiagnosis and unnecessary treatment.