Clinical Neurophysiology: April 2023

Long term symptoms following COVID-19 (Long COVID) now affects a large number of patients with estimates of up to 100 million people world-wide.

Prolonged “long-COVID” (P-L–COVID), seen several months after even a mild COVID-19 infection, is characterized by a complexity of neuromuscular, musculoskeletal, and neuropsychiatric symptoms, including Fatigue, myalgia, headache, problems with memory and concentration (“brain fog”), chest pain, palpitations, sensory disturbances, depression and anxiety, joint pain and insomnia are the most prevalent described symptoms, that collectively affect the patients’ quality of life.

In order to further explore whether myopathy might be a common finding in Long COVID patients, authors aimed to examine a larger cohort of Long COVID patients in a Post COVID Clinic with fatigue and musculoskeletal symptoms. The authors aimed also to examine a possible neuromuscular transmission failure which could be a cause of fatigue. 

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Using single-fiber electromyography (EMG) and based on data from 84 patients with long COVID, this study showed that shorter motor unit potentials were noted in more than half of the patients, with some having increased muscle jitter on EMG.

Muscle pathology suggested abnormal motor endplates.

Previous studies have suggested myopathic changes in patients with long COVID symptoms.

The wide variety of histological changes suggests that skeletal muscles may be a major target of SARS-CoV-2, causing muscular post-COVID-19 symptoms. Because most patients had mild-moderate acute affection, the new variants that might cause less severe acute disease could still have the ability to cause long-term myopathy.

This study using quantitative EMG and single-fiber EMG confirms some of the previous findings.

New pathological abnormalities suggesting damage to the terminal nerves and motor endplate were noted in this study.

Conclusions

Myopathic changes are common in Long COVID. sfEMG abnormality is less common but may correlate with clinical scores. sfEMG changes may be due to motor endplate pathology.

Significance

These findings may indicate a muscle pathophysiology behind fatigue in Long COVID.