Atlanto-Axial Instability

Question:

Can a person with Down syndrome develop atlanto-axial instability in adulthood? My son is 47. When he was younger, X-ray screenings for atlanto-axial instability were negative. Recently, he has started to hold his head to one side, sit at the table with his head on his hand like it is too heavy, and limp/walk differently. Where should I start for an evaluation? PCP? Neurologist? Down syndrome specialist? Could you recommend where a provider might find information regarding AAI and Down syndrome?

Answer:

​Atlanto-axial instability (AAI), the slippage of the position of the first vertebrae in the neck compared to the position of the second, is more common in people with Down syndrome (DS) than those without DS. It is called AAI because the first vertebrae in the neck (cervical) is the atlas and the second is the axis. This is the joint in the spine that is most likely to develop this slippage or mispositioning. However, this slippage can occur in the positioning of any vertebrae in the cervical spine as well as the thoracic and lumbar part of the spine. The particular concern with AAI or instability anywhere in the spine is that the canal formed by the vertebrae is where the spinal cord sits. If the canal becomes narrowed, the spinal cord can get “pinched” (compressed), and damage to the spinal cord (which can cause neurologic impairments) can occur (see below). The narrowing of the spinal canal is also called spinal stenosis.

As anyone ages, osteophytes (bone spurs), thickening of ligaments, herniation of discs, fractures, tumors, and other conditions can cause narrowing of the spinal canal (even if instability is not present). Fortunately, solid tumors are less common in general in people with DS and, therefore, would be an unusual cause of spinal stenosis. In our experience, we have seen several people with DS with spinal stenosis caused by osteophytes due to arthritis and/or ligamentous thickening.

Per this article by the Cleveland Clinic, neurologic impairments associated with spinal cord compression include:

• Neck pain
• Numbness or tingling in the arm, hand, leg, foot, or anywhere below the point of the nerve compression
• Weakness or clumsiness in the arm, hand, leg, or foot
• Problems with balance
• Loss of function in hands, like having problems writing or buttoning shirts
• Loss of bladder or bowel control (in severe cases)

These symptoms can be seen whether the spinal cord compression is related to instability or one of the other causes. In addition, we have found spinal stenosis or cervical instability in people with DS who presented with:

• Holding their head in unusual positions
• Not wanting to participate in activities

In our experience, the symptoms of weakness, tingling, clumsiness, and loss of hand function can be bilateral (both sides of the body) or unilateral (only one side).

AAI is diagnosed by taking the history from the person with DS and family and doing a physical exam to assess for the above concerns as well as:

• Increased deep tendon reflexes including clonus (a repetitive movement of the feet and/or hands found by extending the wrist or ankle with gentle force)
• Abnormal plantar reflex (big toe goes up with stroking plantar surface of the foot)

Further evaluation for AAI and/or cervical spinal stenosis may include:

• X-rays of the cervical spine, particularly, those done in flexion (with the head tilted forward) and extension (with the head tilted back)
• An MRI of the cervical spine to assess for spinal stenosis and injury to the spinal cord. It is sometimes done in flexion and extension.
• A CT scan of the cervical spine to assess the anatomy of the cervical spine
• Additional testing such as an EMG (electromyogram). This may be done if the diagnosis is not certain based on other testing.

Upon diagnosing AAI, other cervical instability, or spinal stenosis that is causing spinal cord compression, symptoms, and/or spinal injury (as seen on MRI), we refer to an orthopedic spine surgeon and/or a neurosurgeon. We recommend physicians who are experienced in treating people with DS. Recommendations for finding a healthcare provider with experience in treating people with DS can be found here. Depending on the availability of a surgeon in the local community, sometimes a referral to a surgeon in a bigger medical center and/or a university might be indicated. Anesthesiologists and physicians assisting with post-operative care (including intensivists who may be providing care since the person will often spend some time in the Intensive Care Unit after surgery) who are familiar with people with DS can also be invaluable.

The specifics of the surgical techniques, the success rate, complications, and the plan of care in the hospital where the surgery is done are beyond my scope and should be discussed with the surgeon.

Considerations for anesthesia

In the operating room, when a person is intubated (a breathing tube placed in the airway to assist breathing while under anesthesia), one option for placing the breathing tube is extending the neck (tilting the head backwards). When the person’s neck is moved like this to intubate, it can cause the spinal cord to get compressed, particularly when the individual has instability of the cervical spine. There is concern that spinal injury can occur in people with DS whether they have instability or not. Normal lateral cervical x-rays in flexion and extension do not seem to indicate that spinal injury will or will not occur when extending the neck during surgery. The anesthesiologist can avoid the problem by using a scope to visualize the airway rather than bending the neck back to intubate.

More information on AAI for families and healthcare providers

Podcast Episode on AAI

GLOBAL Medical Care Guidelines for Adults with Down Syndrome

Down Syndrome Medical Interest Group (DSMIG-USA)
DSMIG-USA is an organization of healthcare professionals who can support providers with less experience caring for individuals with Down syndrome.