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Objective: To investigate the association between changes in anti-acetylcholine receptor antibody (AChR Ab) levels induced by immunosuppressive treatment and myasthenia gravis (MG) prognosis at 1-year post-treatment in patients with MG., Methods: We included 53 consecutive AChR Ab-positive patients with MG whose AChR Ab levels were remeasured within 100 days of initiating immunosuppressive treatment (median remeasuring time post-treatment: 71 (55-84) days). The AChR Ab level reduction rate (RR-AChRAb, %/day) adjusted for the time between treatment initiation, and AChR Ab level remeasurement was calculated as follows: (pretreatment-post-treatment AChR Ab level)/pretreatment AChR Ab level/days between therapy initiation and AChR Ab level remeasurement ×100. Participants were divided into two groups based on the cut-off value of RR-AChR Ab, determined using receiver operating characteristic analyses for achieving minimal manifestation (MM) or better status at 1-year postimmunosuppressive treatment. The Myasthenia Gravis Foundation of America postintervention status and MG activity of daily living (MG-ADL) score at 1-year post-treatment were compared between the two groups., Results: The RR-AChRAb cut-off value was 0.64%/day. The high RR-AChRAb group had a higher ratio of MM or better status (90% vs 65%, p=0.03) and lower MG-ADL score (median; 1 vs 2, p=0.04) than the low RR-AChRAb group. Kaplan-Meier analyses showed the early MM achievement in the high RR-AChRAb group (p=0.002, log-rank test)., Conclusions: High RR-AChRAb is associated with a favourable outcome at 1-year post-treatment. AChR Ab remeasurement within 100 days of therapy may be useful for predicting AChR Ab-positive MG outcomes at 1-year post-treatment., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: Myasthenic symptoms can be present in patients with amyotrophic lateral sclerosis (ALS). These symptoms have been considered to be caused by the degeneration of distal motor neurons and the neuromuscular junction (NMJ). Recent studies suggested that antibody to low-density lipoprotein receptor-related protein 4 (LRP4) was a pathogenic agent of myasthenia gravis (MG), and it was also detected in ALS patients., Case Presentation: Patient 1: A 58-year-old Japanese man developed progressive weakness and subsequent myasthenic symptoms including oculomotor disturbance. Clinical examination and electrophysiological studies confirmed upper and lower motor neuron involvement and NMJ dysfunction, and anti-LRP4 antibody was detected in his serum. A series of immunotherapies, including steroid pulse therapy, intravenous immunoglobulin, and plasmapheresis, was performed, and the myasthenic symptoms partially improved. The titer of anti-LRP4 antibody subsequently decreased. However, the therapeutic effect was transient, and ALS symptoms progressed. His clinical findings fulfilled the criteria of probable ALS using the Awaji criteria. Patient 2: A 74-year-old Japanese man suffered from progressive weakness of all limbs and dropped head in the evening. He complained of diplopia with a lateral horizontal gaze. Probable ALS was diagnosed because of the upper and lower motor neuron signs, whereas anti-LRP4 antibody was detected. Several immunotherapies were administered, and the myasthenic symptoms partially responded to each therapy. However, the truncal muscle weakness progressed, and he died of respiratory failure., Conclusion: We report two anti-LRP4 antibody-seropositive ALS patients with myasthenia who were not typical of ALS patients, and showed partial responses to immunotherapies. The anti-LRP4 antibody-seropositive status may influence developing ALS and cause additional ALS symptoms.