Post COVID-19 Chronic Fatigue
One of the most common symptoms reported in COVID-19 survivors is fatigue. (20) In a study completed in Dublin, more than half of recovered COVID-19 patients experienced post-viral fatigue syndrome, regardless of the severity of their initial COVID-19 symptoms. (21) Fatigue, along with many other symptoms of Post COVID syndrome, resemble Chronic Fatigue Syndrome, also known as Myalgic Encephalitis (ME), a chronic condition characterized by at least 6 months of fatigue, in addition to other symptoms such as sore throat, headache, muscle pain, joint pain, post-exertional fatigue, sleep disruption, cognitive disturbance (or ‘brain fog’), and secondary anxiety or depression. (22,23)
CFS/ME has long been misunderstood, but recent research suggests viral-mediated neuroinflammation, (24) reduced ability for cells to utilize ATP, a small molecule that provides energy to our cells; (25) and viral-mediated gene up regulation may be play a role in pathogenesis. (26) Many patients diagnosed with CFS/ME report that their illness began following a bout of an acute infectious disease, often mononucleosis or the flu. (27)
Chronic fatigue following a viral infection is not unheard of; studies of SARS-CoV-1 patients reported chronic fatigue for years following infection. (28, 29) Persistent fatigue has also been noted following cases of H1N1, (30) and the West Nile virus. (31) Although this link has been made, the mechanism remains murky.
But CFS/ME may hold the key to understanding Post COVID syndrome, particularly with respect to lymphatic involvement. Lymphatic drainage from the brain occurs via a space surrounding the olfactory nerves, through the cribriform plate, into the nasal mucosa. (32) A proposed component of the pathogenesis of CFS/ME is a disturbance in lymph drainage along this pathway, and subsequent build-up of pro-inflammatory cytokines within the central nervous system.(33, 34) Without adequate drainage, various molecules can accumulate within the brain.
If these molecules are pro-inflammatory, chronic inflammation within the nervous system can ensue, leading to detrimental effects on the nervous system. SARS-CoV-2 is suspected to penetrate the nervous system via the neuro-mucosal interface of olfactory mucosa, which may explain the anosmia (loss of smell) associated with COVID-19. (35) As a result, SARS-CoV-2 may disrupt lymph drainage from the brain, leading to an accumulation of pro-inflammatory cytokines, similar to the proposed mechanism of CFS/ME. (36,37) Inflammation triggered by these cytokines could instigate short-term symptoms, such as fever, as well as long-term symptoms, such as chronic fatigue, altered sleep-wake cycle, and cognitive dysfunction, symptoms characteristic of Post COVID ‘long-haulers’. (36)
Unfortunately, symptoms of CFS/ME patients were initially believed to be psychosomatic when doctors first identified this condition more than 70 years ago, and this stigma remained until fairly recently. The lack of a formalized test to diagnose this condition hindered clinical progress, as diagnosis relied solely on self-reporting of symptoms.
However, research connecting viruses as triggers for CFS/ME has helped begin the process of de-stigmatization. CFS/ME may provide the key to understanding Post COVID Syndrome. In turn, the attention Post COVID syndrome has garnered may finally provide solace for the CFS/ME community that was largely neglected by academia, or worse - told to ’try to exercise’ or go to psychotherapy, in order to feel better.(27, 38)