| Clinical neurophysiology  

Myopathy as a cause of Long COVID fatigue.

An interesting neurophysiological and histopathological study that demonstrated structural abnormalities in muscles of patients with musculoskeletal Long COVID symptoms.

Long term symptoms following COVID-19 (Long COVID) affects up to 100 million people world-wide, and fatigue and myalgia are the most prevalent symptoms.

A recent study identified neurophysiological abnormalities in patients with musculoskeletal Long COVID symptoms, correlating quantitative electromyography (qEMG) and single-fiber EMG (sfEMG) results to clinical scores and histopathology (1).

Eighty-four patients with musculoskeletal Long COVID symptoms underwent qEMG, sfEMG and muscle biopsy. The authors reported that 52% of patients showed a decreased duration of mean motor unit potential in ≥1 muscles, while an increased mean jitter was observed in tibialis anterior of 17% of patients and in extensor digitorum communis of 25%. Increased jitter was observed with or without myopathic qEMG. A significant correlation between low quality of life score and higher jitter values was found, whereas no correlations with qEMG measures were observed. Muscle biopsies were performed in a subgroup of patients, revealing a damage of terminal nerves and motor endplate, where axons were present but no vesicle containing terminals. The post-synaptic cleft in areas appeared atrophic with short clefts and coarse crests. These changes were in line with previous muscle histopathology findings in 16 Long COVID patients (2).

The data supported the presence of myopathic changes in Long COVID, through alterations in qEMG, while sfEMG abnormalities were less common. However, sfEMG changes correlated with clinical scores. The histopathological features associated to sfEMG alterations suggested a motor endplate pathology. These findings revealed the presence of neuromuscular pathology in Long COVID patients, highlighting the importance to recognize adequate therapeutic options.  


Key Points:

  • Fatigue and myalgia are frequent symptoms of Long COVID.
  • Neurophysiological and histopathological abnormalities could be detected in patients with musculoskeletal Long COVID symptoms.
  • These findings may indicate a muscle pathophysiology in Long COVID.


  1. Agergaard J, Yamin Ali Khan B, Engell-Sørensen T, Schiøttz-Christensen B, Østergaard L, Hejbøl EK, Schrøder HD, Andersen H, Blicher JU, Holm Pedersen T, Harbo T, Tankisi H; MULTICOV Consortium. Myopathy as a cause of Long COVID fatigue: Evidence from quantitative and single fiber EMG and muscle histopathology. Clin Neurophysiol. 2023 Apr;148:65-75. doi: 10.1016/j.clinph.2023.01.010.
  2. Hejbøl EK, Harbo T, Agergaard J, Madsen LB, Pedersen TH, Østergaard LJ, Andersen H, Schrøder HD, Tankisi H. Myopathy as a cause of fatigue in long-term post-COVID-19 symptoms: Evidence of skeletal muscle histopathology. Eur J Neurol. 2022 Sep;29(9):2832-2841.

Publish on behalf of the Scientific Panel on Clinical neurophysiology