Around 1.2 million people in the UK are living with long COVID – a condition where patients still experience symptoms from four weeks to over a year after catching COVID-19.
Some of the symptoms are consistent with what we know about COVID-19. The 39 per cent of long COVID cases that have shortness of breath could be linked to the damage the coronavirus can cause to lungs, while a third of people with long COVID still experience the loss of smell common with COVID-19 infection.
However, the most common long COVID symptom reported is fatigue, which has made some question whether the condition could in fact be the same as chronic fatigue syndrome (CFS).
Also referred to as myalgic encephalomyelitis (ME), CFS is a long-term condition that makes people experience extreme fatigue, particularly after exercise, in addition to problems sleeping, bodily pain and confusion known as brain fog. Scientists still don't know what causes ME/CFS, but many patients' onset of the condition follows infection with a virus or bacteria.
Until now, experts haven't been able to confidently say whether ME/CFS is a part of long COVID. But a new study, by researchers at Icahn School of Medicine at Mount Sinai in New York, has tested 41 patients against ME/CFS diagnostic criteria.
Of the group, 46 per cent had four or more symptoms of ME/CFS and had experienced a substantial impact to their lives as a result of fatigue. A further 13 long COVID patients met the criteria but were excluded on account of having a large BMI or a cardiac disease.
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The team then ran cardiopulmonary exercise tests with the group, to assess how their breathing was affected by activity. Patients were told to pedal on a stationary bicycle until they reached point of exhaustion, while the difficulty was increased by 25 Watts every three minutes.
Nearly all of the patients (36 of 41) showed abnormal breathing – rapid, shallow breathing similar to that of people with asthma – and a majority had chronic hyperventilation after the exercise test.
“Many of these patients reported shortness of breath, and the cardiopulmonary exercise test is often used to determine its underlying cause," explained Dr Donna Mancini, professor in the department of cardiology and lead author of the study.
“These findings suggest that in a subgroup of [long COVID patients], hyperventilation and/or dysfunctional breathing may underlie their symptoms. This is important, as these abnormalities may be addressed with breathing exercises or ‘retraining’,” said Mancini.
Mancini said there could be several subsets of patients with long COVID, including those who have ME/CFS-like symptoms.
This theory is echoed by Dr David Strain, medical advisor to the charity Action for ME, who was not involved in the research but spoke toBBC Science Focusabout its implications.
While Strain believes the study is a promising start, there is one difference in the research's methods compared with typical ME/CFS studies. "One of the key criteria for ME is post-exertional malaise, and we test for that by repeating the [exercise tests] over two consecutive days. Then we are not only looking for the respiratory impairment on day one but also the difference between day one and day two tests."
"It is very likely that a subset of people with long COVID are actually suffering from ME with a known viral trigger, as compared with the 250,000 people who have ME without knowing the original cause. A greater understanding of both conditions will be to the benefit of all, particularly as we start to explore treatment options," said Strain.
