Abstract
Soon after the outbreak of coronavirus disease 2019 (COVID-19), unexplained sustained
fatigue, cognitive disturbance, and muscle ache/weakness were reported in patients
who had recovered from acute COVID-19 infection. This abnormal condition has been
recognized as “long COVID (postacute sequelae of COVID-19 [PASC])” with a prevalence
estimated to be from 10 to 20% of convalescent patients. Although the pathophysiology
of PASC has been studied, the exact mechanism remains obscure. Microclots in circulation
can represent one of the possible causes of PASC. Although hypercoagulability and
thrombosis are critical mechanisms of acute COVID-19, recent studies have reported
that thromboinflammation continues in some patients, even after the virus has cleared.
Viral spike proteins and RNA can be detected months after patients have recovered,
findings that may be responsible for persistent thromboinflammation and the development
of microclots. Despite this theory, long-term results of anticoagulation, antiplatelet
therapy, and vascular endothelial protection are inconsistent, and could not always
show beneficial treatment effects. In summary, PASC reflects a heterogeneous condition,
and microclots cannot explain all the presenting symptoms. After clarification of
the pathomechanisms of each symptom, a symptom- or biomarker-based stratified approach
should be considered for future studies.
Keywords
long COVID-19 - microclots - SARS-CoV-2 spike protein - coagulation - platelets
