Subclinical myopathic changes in COVID-19

Coronavirus disease 2019 (COVID-19) is associated to neuromuscular symptoms in up to 10.7% of hospitalized patients. Nevertheless, the extent of muscular involvement in infected subjects with no signs of myopathy has never been assessed with neurophysiological investigations.

Over a 3-week period - from April 30 through May 20, 2020 - a total of 70 patients were hospitalized in the Internal Medicine Ward of the Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico in Milan, Italy. After excluding patients who underwent invasive ventilation and steroid treatment, 12 patients were evaluated. Nerve conduction studies (NCS) included the analysis of conduction velocity, amplitude, and latency for bilateral motor tibial, ulnar nerves, and sensory sural and radial nerves. Unilateral concentric-needle electromyography (EMG) was performed evaluating at least 4 areas of 8 selected muscles. For each muscle, spontaneous activity at rest, morphology, and recruitment of motor unit action potentials (MUAPs) were evaluated.

While nerve conduction studies were unremarkable, needle electromyography showed myopathic changes in 6 out of 12 subjects. All patients were asymptomatic for muscular involvement. Clinical features and laboratory findings did not show relevant differences between patients with and without myopathic changes.

Our data show that in SARS-CoV-2 infection muscular involvement can occur despite the absence of clinical signs or symptoms and should be considered part of the disease spectrum. The application of muscle biopsy to unravel the mechanisms of myofiber damage on tissue specimens could help to clarify the pathogenesis and the treatment response of coronavirus-mediated injury.