Differential Response to Corticosteroids in Immune-Mediated Myokymia vs Grouped Fasciculation Discharges

Myokymia and grouped fasciculation discharges (GFD) are electromyographic manifestations of peripheral nerve hyperexcitability syndromes. This case series explores the differential response to corticosteroids in patients with myokymia compared to those with GFDs. Six patients were included in this report: three with predominant myokymia and three with predominant GFDs, reviewed between March 2023 and February 2024. Electromyographic examinations were performed on various muscle groups, with the gastrocnemius EMG findings serving as an index. The neurologist conducting the EMG was blinded to the clinical history. Patients with predominant myokymia showed a positive response to corticosteroids. In contrast, patients with GFDs, characterized by non-rhythmic, irregular discharges, exhibited a limited response requiring higher immunotherapy. This study potentially highlights the importance of EMG in guiding treatment decisions, demonstrating that patients with myokymia respond well to corticosteroids due to underlying autoantibody-mediated potassium channel dysfunction.