Muscle disease in severe COVID-19 patients: a microangiopathic myopathy.

Patients surviving coronavirus disease of 2019 (COVID-19) often complain of skeletal muscle weakness that may be very limiting and long-lasting. There are almost no studies on the skeletal muscle of these patients, and electron microscopic data are scarce. We assessed the ultrastructural changes in the quadriceps of eight patients with COVID-19 and found a combination of features different from those reported in corticosteroid myopathy and acute relaxant-steroid myopathy. The most remarkable and constant changes involved the endothelial cells and consisted of massive amounts of pinocytotic vesicles, degenerative changes, platelet aggregates and, most characteristic of all, an increase in the external lamina thickness that seems to stem from reduplication due to successive bouts of endothelial cell damage and subsequent regeneration. Viral particles were not found in any of the cases. This distinct and quite common set of alterations defines the myopathy associated with infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This association seems to be the result of an inflammatory process that would arise in infected cells but could damage non-infected endomysial blood vessels, thus resulting in persistent changes of the microvasculature that would be related to long-standing myopathic clinical features.