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Unfortunately, there are a group of Chiarians (people with Chiari) that also suffer from related conditions. The experts have just recently found these connections, and research is ongoing. For these lucky people, treatment becomes much more complicated and ongoing.

The group of related conditions includes:

Ehlers-Danlos Syndrome (EDS)
Tethered Cord Syndrome (TCS)
and for an even luckier few,
Postural Orthostatic Tachycardia Syndrome (POTS)

The doctors at The Chiari Institute in Manhasset, New York have reported a subset of patients that suffer from these related conditions.

Ehlers-Danlos Syndrome is a disorder of the connective tissues, which are tissues that support the skin, bones, blood vessels, and other organs. Defects of connective tissue result in hypermobile joints and fragile skin. On its own, EDS can range from very mild to life-threatening symptoms. When connected to Chiari, the most worrisome complication is Cranio-Cervical Instability. This means that the occipito-atlantal joint is hypermobile, or that the head is wobbly on the spine. Patients with Chiari and EDS tend to have difficulty sitting up, because certain brain structures tend to slide and sag upon upright posture. Also, the odontoid bone at the top of the spine tends to poke into the brainstem. The symptoms of this instability are therefore worsened by sitting up, and relieved by lying down. Symptoms include nausea, difficulty swallowing, difficulty supporting the head, and quite a few other "brainstem" symptoms.

Cranio-Cervical Instability is treated with a surgery called a Cranio-Cervical Fusion. The procedure involves precisely extracting the skull and positioning the head on the neck, then fusing the first four vertebrae to the bottom of the skull and implanting two metal rods with bolts and screws around the skull to create more stability for the head and neck.

Many Chiari/EDS patients develop a related syndrome called dysautonomia or POTS. POTS stands for:

Postural (meaning related to posture)
Orthostatic (meaning standing)
Tachycardia (meaning fast heartrate)
Syndrome (meaning a collection of symptoms).

POTS is a syndrome caused by dysregulation of the autonomic nervous system. In chiari/EDS patients, this is thought to be a result of brainstem dysregulation. The functions of the autonomic nervous system include heartrate, blood pressure, temperature control, pupil dilation, digestion, and many more "automatic" body functions. So dysregulation can lead to problems with any of these. The distinguishing feature of POTS is a rise in heartrate of at least 30 beats per minute upon standing. People with POTS tend to get out of breath and tired very easily, because their bodies are working so hard just to keep their brain oxygenated.

Even more recently, doctors have noted a connection between Chiari, EDS, and Tethered Cord Syndrome (TCS).

Tethered Cord Syndrome is a condition where the spinal cord forms attachments that limit the movement of the spinal cord within the spinal column. This causes a downward stretching of the spinal cord.

Recently, a new form of TCS has been recognized. It is called Occult Tight Filum Terminale. The filum terminale is like a thin elastic band, about 8 inches long. It extends from the bottom of the spinal cord to the tip of the tail bone. When the filum is fat-filled, fibrous and tight, it will not allow the spinal cord to move up and down within the spinal column, and so the spinal cord and the nerves end up being stretched instead of the filum. In most people this causes nerve damage.

Tethered spinal cord syndrome may go undiagnosed until adulthood, when sensory and motor problems and loss of bowel and bladder control emerge. This delayed presentation of symptoms is related to the degree of strain placed on the spinal cord over time.

To treat this problem, the spinal cord needs to be "detethered". The operation to fix this is called a Section Filum Terminale. In this surgery, the spinal cord is separated from the tailbone by clipping the filum terminale, This allows the spinal cord to hang freely within the spinal column.