Persistent neuromuscular dysfunction in long COVID: A quantitative and single fiber EMG follow-up study

Persistent symptoms after SARS CoV-2 infection, often designated as "long COVID", continue to be an ongoing health issue. Previously, we reported electromyography (EMG) and single fiber EMG (SFEMG) abnormalities in long COVID. This study aimed to assess the long-term neuromuscular manifestations of long COVID.

In this follow-up study, fifty patients (39 females and 11 males, mean age at baseline: 48.1 ± 9.3 years) with long COVID showing myopathic (EMG and/or abnormal SFEMG at diagnosis were re-evaluated. The disease duration was 1.2 ± 0.6 years at baseline. The mean follow-up interval was 1.38 years. Quantitative EMG (qEMG) was performed on the biceps brachii (BB), vastus medialis (VM), and tibialis anterior (TA), while SFEMG was performed on the extensor digitorum communis (EDC) and TA, at baseline and follow-up on the same muscles and side. EMG, SFEMG, and clinical scores were compared using paired parametric or nonparametric tests.

Fatigue Assessment Scale (FAS) scores were unchanged (35.8 ± 7.7 vs 34.0 ± 9.4; p > 0.05). Motor unit potential (MUP) amplitudes and durations increased in BB, TA, and VM (p = 0.0001), while the frequency of polyphasic potentials remained unchanged (p > 0.05). SFEMG findings in TA and EDC were also unchanged (p > 0.05). At baseline, 78% of individuals showed myopathic qEMG and 54% abnormal SFEMG; at follow-up, 18% had myopathic qEMG, 56% abnormal SFEMG, and 40% showed normal EMG and SFEMG.

Myopathic changes decreased over time; however, SFEMG abnormalities and clinical scores remained persistent. These findings suggest ongoing neuromuscular dysfunction, although other mechanisms may also contribute to persistent long COVID symptoms.