Vertebral column

The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs. The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

Chiari I malformation
A Chiari malformation (CM) is a structural defect of the base of the skull and the cerebellum, characterized by a downward displacement of one or both cerebellar tonsils through the foramen magnum (the opening at the base of the skull). This can sometimes lead to non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid(CSF) outflow.

While many clinical criteria consider Chiari malformation to be a differential diagnosis, a Swedish study of 234 ME/CFS patients meeting the Canadian Consensus Criteria found that a substantial proportion of patients had signs on their brain MRIs suggestive of intracranial hypertension: 55% had increased diameter of the optic nerve sheath. In addition 80% had cerebellar tonsillar descent that could potentially cause disruptions to spinal fluid flow, and thus increased intracranial pressure. 13.2% had tonsillar herniations severe enough to be considered a Chiari Malformation.

Craniocervical instability
Craniocervical instability (CCI) is a pathological condition of increased mobility at the craniocervical junction, the area where the skull meets the spine. In CCI the ligamentous connections of the craniocervical junction can be stretched, weakened or ruptured.

CCI usually develops as a result of physical trauma such as a car accident, an inflammatory disease such as rheumatoid arthritis or a congenital disorder such as Down's syndrome. More recently, physicians have reported an increased prevalence of CCI in patients with hereditary disorders of connective tissue such as Ehlers Danlos Syndromes (EDS). There have also been anecdotal reports of patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) who were later diagnosed with CCI,   although no scientific publication on this subject exists. It frequently co-occurs with atlantoaxial instability (AAI).

ME/CFS
Craniocervical instability

Cervical stenosis

Tarlov cysts

Fibromyalgia
Chiari malformation

Ehlers-Danlos Syndrome
Several pathologies of the spine have been associated with Ehlers-Danlos Syndrome. (Link to and reference Henderson et al)

Related

 * Brain
 * Spinal cord