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

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.

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.

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.

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.

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.