For survivors of severe COVID-19, overcoming the virus is just the beginning of an uncharted recovery path. As the number of confirmed COVID-19 cases exceeds 27 million globally and 6 million in the US, the number of patients who experience persistent symptoms during recovery is rapidly growing. In COVID-19 patients, common acute symptoms include cough, fever, dyspnea, musculoskeletal symptoms (myalgia, joint pain, fatigue), gastrointestinal symptoms, and anosmia/dysgeusia . Clinicians and researchers have focused on the acute phase of COVID-19, but continued monitoring and treating of persistent symptoms is urgently needed. Recent studies assessed persistent symptoms in patients who were discharged from the hospital after recovering from COVID-19. None of the patients had a fever or any of the other signs or symptoms associated with acute illness. Nevertheless, decreased quality of life was observed in 44.1% and fatigue was reported by 53.1% and 71% of patients. Furthermore, persistent fatigue following COVID-19 infection is common and independent of severity of initial infection (hospitalized and non-hospitalized patients). In addition to the characteristic laboratory findings and lung computed tomography (CT) abnormalities, it has been recently reported that patients with COVID-19 also have neurological manifestations. Wu et al. [2020] found that viral infections have detrimental impacts on neurological functions and can even cause severe neurological damage. Their study showed that coronaviruses (CoV), especially severe acute respiratory syndrome CoV 2 (SARS-CoV-2), exhibited neurotropic properties and may cause neurological diseases with severe fatigue symptoms. Another recent case report has also indicated reduced glucose uptake ([18F]flurodeoxyglucose (FDG); measured with positron emission tomography (PET)) in diverse brain areas [9], which may contribute to these neurological manifestations. Therefore, there is a critical need to develop inexpensive, effective, and rapid treatments for the persistent fatigue experienced by recovered COVID-19 patients. Without such treatments, these patients will continue to experience fatiguing symptoms that significantly reduce their quality of life. One possible treatment modality is transcranial direct current stimulation (tDCS) [10]. tDCS uses weak currents applied to the scalp to alter the excitability of cortical neurons by changing their spontaneous firing rate. It also has a favorable safety profile and only transient adverse side effects. Studies in patients with neurological disorders have shown that tDCS over the primary motor and/or sensory cortex (M1/S1) consistently and significantly improves fatigue. M1 tDCS represents an easy, cost-effective candidate for treating persistent fatigue in recovered COVID-19 patients.
The objective of this study is to investigate the short- and long-term effects of multiple sessions of 4 mA M1 tDCS on fatigue and brain activity in recovered COVID-19 patients using established measures of perception of fatigue, performance fatigability, and cerebral glucose uptake. Our central hypothesis is that tDCS will improve fatigue short- and long-term, and thus will improve quality of life (QOL) in recovered COVID-19 patients and that these changes will be associated with alterations in brain activity.