Long COVID and myalgic encephalomyelitis/ chronic fatigue syndrome (ME/CFS) both seem to impact the oldest parts of the brain in a curiously similar fashion.

Using a high-resolution version of magnetic resonance imaging ( MRI), researchers in Australia have shown the brainstem regions of 10 ME/CFS patients and 8 long COVID patients are significantly larger than those of 10 healthy control subjects.

The brainstem connects the spinal cord to the largest part of the brain, the cerebrum. From the top down, the stem comprises the midbrain, the pons, and the medulla oblongata.

The pons, which is Latin for bridge, is involved in unconscious processes such as sleep and wake cycles as well as the regulation of our breathing rate and pain processing.

The medulla oblongata, meanwhile, connects to the 'little brain' or hindbrain, the cerebellum, via a series of rope-like nerve tracts. The cerebellum rests atop the brain stem and helps coordinate balance and movement.

In the current study, the larger these brainstem regions were in volume, the more likely patients were to complain of breathing difficulties or pain in questionnaires.

"Therefore," researchers from Griffith University write, "brainstem dysfunction may contribute to the respiratory-related symptoms in ME/CFS and long COVID."

This is a small study, but it demonstrates a neurological overlap between ME/CFS and long COVID for what the authors claim is the first time.

The findings could help explain the many shared symptoms between the two conditions, such as brain fog, dizziness, headaches, unrefreshing sleep, shortness of breath, body aches, fatigue after exertion, and heart rate and blood pressure issues.

Ever since scientists reported on the first long COVID patients in 2020, experts and patients alike have pointed out how similar the viral fallout of SARS-CoV-2 is to symptoms of ME/CFS.

Many suspect the two illnesses are related or even triggered by the same factors, which means that research on one could help us understand and treat the other.

Indeed, studies show between 13 and 58 percent of people with long COVID meet the diagnostic requirements for ME/CFS. However, given the lack of consensus on how to diagnose these conditions, such numbers are uncertain.

At this stage, scientists don't know enough about either condition to say anything for sure. And that has less to do with these diseases' 'mysterious' nature and more to do with a sheer lack of research.

Even before COVID-19 came to our attention, the health burden of ME/CFS in the US was estimated to be double that of HIV/ AIDS. Yet even then, it's the most underfunded disease in the US National Institute of Health's books based on its relative harm, receiving 7 percent of the funding it should compared to other similar diseases.

To this day, no one really knows what causes ME/CFS, how to effectively diagnose it, or how to treat it. Many cases can be associated with viral infections or immune dysfunction, while others are of entirely unknown origins.

By comparison, long COVID stems from a known virus, and researchers still don't understand how the pathogen wreaks such havoc on the body and mind.

At this point, experts are coming up with more questions than answers, but some major culprits keep popping up.

The brain and the brainstem, in particular, seem to be the stage for a lot of the action.

Recently, studies have found that even people with mild COVID-19 show significant brain changes, like inflammation. And in autopsy studies, those who died of COVID-19 had brains that looked scarily aged.

An analysis based on data from the UK Biobank suggests the brainstem is often increased in volume in those who have contracted COVID-19.

Since the 1990s, researchers have also used MRIs to study the brains of patients with ME/CFS. Compared to healthy controls, inexplicable changes in the volume of certain brain regions is common, and the brain stem is one of the locations that stands out the most.

The advent of newer technology allows scientists a closer look at this part of the brain than ever before.

In their initial research, scientists in Australia found no significant difference in the brainstem volumes of those with ME/CFS and those with long COVID.

"The brainstem regulates respiratory, cardiovascular, gastrointestinal, and neurological processes, and its impairment can explain the overlapping symptoms of ME/CFS and long COVID," the study's authors conclude.

"​​Such volume increases may reflect edema of inflammatory responses, neurodegeneration, and/or viral invasion," they add.

Further research will be needed to determine which of these pathways is leading the brain stem to swell in size and whether those routes are similar or different among patients with ME/CFS and long COVID.

The study was published in Frontiers in Neuroscience.