F43. Electrophysiological tests in patients with anti-MuSK myasthenia gravis: A retrospective study

Abstract

Introduction Myasthenia gravis (MG) with autoantibodies to muscle-specific tyrosine kinase (MuSK) represents a distinct type of disease, as compared MG with antibodies against acetylcholine receptor (AchR-Abs). MuSK-MG patients have peculiar clinical features characterized by predominant oculo-bulbar symptoms and a lack of response to conventional MG treatments. Since the role of electrophysiological tests in MuSK patients is still argued, our aim was to investigate their electrophysiological profile in order to arise a light over this darkness. Methods We retrospectively evaluated repetitive nerve stimulation (RNS) and single-fibre electromyography (SF-EMG) reports of 63 MuSK patients, at the time of MG diagnosis, and we compared them with 35 non-timomatous AChR-Abs positive patients matched with MuSK group according to gender, age at onset of MG, age at MG diagnosis and severity of the disease. Disease severity was graded according to Myasthenia Gravis Foundation of America (MGFA) classification. Seronegative patients and thymoma-associated MG patients were excluded from the study. Results Sixty-three MuSK patients (11 males; 52 females; mean age at MG onset: 37 ± 2.0; mean age at diagnosis: 38.7 ± 2.0) and 35 AChR-Abs positive patients (9 males; 26 females; mean age at MG onset: 31.2 ± 2.7: mean age at diagnosis: 33.1 ± 2.5) were enrolled in the study. Fifty-nine MuSK patients (93.6%) and 31 AChR-Abs positive patients (88.5%) underwent RNS, whereas SF-EMG was tested in 17 MuSK patients and in 7 AChR-Abs patients. RNS showed a significant decrement in a higher percentage of AChR-Abs positive patients than the MuSK group (p Conclusion While SR-EMG positivity was significantly higher in AChR-Abs group, there was no difference regarding SF-EMG. In MusK group, the decrement of RNS was more evident in proximal muscles while RNS in distal muscles can be negative. Although neurophysiological evaluation is still important for MG diagnosis, it plays a secondary role after anti-MuSK titration.