Brainstem

The brainstem includes the midbrain, pons, and medulla oblongata, and is structurally contiguous with the spinal cord. It connects the brain to the motor and sensory functions of the peripheral nervous system and plays an important role in the autonomic nervous system, including regulation of heart rate, respiratory function, consciousness, sleep/wake cycle, and digestion.

Brainstem compression & deformation
Brainstem deformation, which can include compression, stretching or changing of shape, can occur as a result of Chiari malformation, craniocervical instability, syringomyelia, and cervical spinal stenosis.

Evidence
Mechanical brainstem compression can be directly responsible for dysautonomia and fatigue. Several research studies have shown that when patients had a fusion surgery to correct their brainstem compression, their symptoms of brainstem compression significantly improved or resolved completely.

There are anecdotal accounts of all ME/CFS symptoms, including postural orthostatic tachycardia syndrome (POTS) and fatigue, going away after a craniocervical fusion to correct the brainstem compression.

As the brainstem is central to regulating the autonomic nervous system (ANS), it is perhaps unsurprising that dysautonomia (such as POTS) can be alleviated by correcting brainstem compression.

Diagnosis
Brainstem compression is diagnosed via dynamic imaging, such as flexion and extension MRI s and rotational CT scans. The most common measurements used to diagnose and quantify brainstem compression are the Clivo-Axial Angle, the Grabb-Oakes Measurement, and the Basion-Dens Interval.

Treatment
A cervical collar can be tried to see if it helps alleviate the neurological symptoms (even if only partially). However, a cervical collar is not an actual treatment for CCI. The standard treatment to correct brainstem compression is a craniocervical fusion surgery, performed by a CCI-literate neurosurgeon.

ME/CFS
A 1995 study found hypoperfusion (reduced blood flow) to the brainstem in patients with ME/CFS. In 2011, a study of brain involvement in CFS found "a strong correlation" brainstem gray matter volume and pulse pressure, "suggesting impaired cerebrovascular autoregulation."

A 2014 Japanese PET study looked at neuroinflammation in 9 patients with ME/CFS and 10 controls. They measured a protein expressed by activated microglia, and found that values in the cingulate cortex, hippocampus, amygdala, thalamus and parts of the brainstem, namely the midbrain, and pons, were 45%–199% higher in ME/CFS patients than in healthy controls. The values in the amygdala, thalamus, and midbrain positively correlated with cognitive impairment score, the values in the cingulate cortex and thalamus positively correlated with pain score, and the value in the hippocampus positively correlated with depression score.