Stimulated Single-Fibre Electromyography (SFEMG) in Ocular and Generalized Myasthenia
Siegfried K. Wagner; Victoria T. Barnett; Tom Tidswell; Saurabh Jain
Royal Free Hospital
London, United Kingdom
Introduction: Patients presenting to eye clinics with variable diplopia, ptosis and generalised muscular weakness are often suspected to have myasthenia gravis(MG). Single-fibre electromyography(SFEMG) which measures NMJ blockade is widely considered to be a more sensitive investigation compared to serology for antibody detection. Our study aimed to characterise clinical findings most predictive for MG, as confirmed by SFEMG and subsequent treatment response.
Methods: Retrospective cohort study(May 2011-January 2016) of patients at a tertiary teaching hospital undergoing investigation for MG, and demonstrating abnormal SFEMG. Data obtained included presenting features, ophthalmic examination and treatment response.
Results: 73 patients(29 male, 44 female, mean age 57, age range 2-92) had SFEMG supportive of ocular-MG. 25 had serology for acetylcholine-receptor antibodies; 7 were positive. Main clinical features were unilateral ptosis(n=16), bilateral ptosis(n=14) and diplopia(n=18). 18 patients had ophthalmoplegia. Only 31 patients(42%) had systemic or non-eye related neurological symptoms. Treatment follow-up was recorded in 40 patients: subjective improvements seen in 6/12 patients on pyridostigmine alone and in 8/8 on combined pyridostigmine and steroids. 7/7 patients improved with additional azathioprine, IVIG, mycophenolate or thymectomy. 3/9 patients improved with monitoring. 4 patients had patching, prisms or surgery.
Discussion: Preceding history of ptosis and/or diplopia was most frequently associated with NMJ dysfunction on SFEMG. Less than half of patients presenting with ocular symptoms had systemic features. Majority of patients commenced on pyridostigmine with steroids subjectively improved, compared to half of patients on pyridostigmine alone.
Conclusion: Ptosis and/or diplopia most commonly predict a MG diagnosis based on a positive SFEMG, and may be the only findings in over half of MG patients. Treatment to stabilise NMJ transmission is effective in 71% ofÂ patients with ptosis and/or diplopia. By comparison antibody testing has poor sensitivity; 46% of patients with negative antibodies responded to myasthenia treatment.