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eMedicine Specialties > Neurology > Pediatric Neurology
Atlantoaxial Instability in Individuals with Down Syndrome
Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital
Updated: Dec 8, 2008
Introduction
Background
The occiput, the atlas (C1), and the axis (C2) form a functional unit, the occipitocervical articulation, which is characterized by a high degree of mobility and little intrinsic bony stability. Strong ligaments facilitate movement and keep these structures in place. Head rotation occurs primarily at this junction, and the odontoid bone is the axis that allows this rotation.1, 2, 3, 4
The atlanto-occipital joints allow movement in extension and flexion. In flexion, an anterior translation of C1 on C2, which normally does not exceed 3 mm in adults, exists. In children younger than 8 years, this translation can be as wide as 5 mm. In pathological conditions (eg, abnormalities of the odontoid bone or in the ligaments that keep these joints together), this displacement increases and bone structures can pressure the spinal cord, producing clinical symptoms.
Pathophysiology
A wide spectrum of congenital and acquired lesions can result in atlantoaxial instability (AAI).5, 6 In individuals with Down syndrome (DS), the excessive laxity of the posterior transverse ligament, which attaches the odontoid bone to C1, is the most common cause of AAI7, but this has not been proven and not every researcher agrees with this issue.8 Other conditions are known to also present with generalized increased laxity of the ligaments (eg, Marfan syndrome, Ehlers-Danlos syndrome). AAI might be a complication.6 Malformations of the odontoid bone also can be a factor in some cases.9
Frequency
United States
AAI with or without subluxation has been reported in as many as 10-30% of individuals with Down syndrome.10, 11 In most instances, the radiologic findings are not associated with clinical symptoms.12 The condition does not necessarily occur more frequently in the United States, although most cases reported to date have occurred in the United States.
Mortality/Morbidity
The primary complications result from spinal cord compression.
In most cases, signs and symptoms progress slowly. The diagnosis can be made, therefore, before the advanced stages of the disease.
Death is unusual but may occur in cases of acute decompensation as a result of respiratory arrest related to compression of the high cervical spinal cord.13
Several studies have shown that serious complications are indeed rare.14
Race
No racial predisposition is known.
Sex
The role of gender is unclear. Most of the studies suggest a female preponderance10, 11, 15; however, some showed a male preponderance16 and others found no difference between men and women.17
Age
Most cases have been described in children.7, 18
Longitudinal studies of children and adults show a high degree of stability both clinically and radiologically.12, 10
In some individuals with radiologic evidence of AAI at the beginning of the study, radiographic findings normalized in subsequent evaluations.
A negative correlation exists between atlanto-odontoid distance and age.19
Clinical
History
Signs and symptoms often result from mechanical compression of the cervical nerve roots and/or spinal cord.20, 21
In some cases, the vertebral arteries may be distorted.
Degenerative disease of the cervical spine, often seen in adults with Down syndrome, may complicate the clinical picture.22, 23, 18, 24, 17
Many early manifestations are of a subjective nature and difficult to elicit in individuals with mental retardation. In some cases, clinical symptoms must be inferred. For example, changes in behavior, refusal to participate in usual activities, changing hand preference, and urinary incontinence in previously continent individuals can be associated with atlantoaxial instability (AAI).
Root compression at C1 and C2 levels produces pain in the upper cervical spine, the neck, and the occipital area that can extend to the head, eyes, ears, and/or throat.
Constant or intermittent vertebrobasilar insufficiency may produce dizziness, vertigo, tinnitus, diplopia, and/or syncope. Unilateral or bilateral tingling and numbness may be present.
In many instances, infections of the pharynx, the middle ear, and/or the upper respiratory tract precede symptoms of AAI. Clinical deterioration following any of these conditions justifies a complete evaluation.25, 15, 9
Physical
Motor system abnormalities are the most common findings at clinical presentation (primarily gait disorders and weakness).
Progressive spasticity in the legs (characterized by increased muscle tone, muscle weakness, ataxic gait, increased deep tendon reflexes, Babinski sign, and clonus) can be a presenting sign.21, 26, 27
In most instances, the neurologic signs and symptoms progress slowly in a matter of weeks.
Children with Down syndrome are hypotonic, and may remain hypotonic even with compression of the spinal cord.
Babinski sign and clonus in the lower extremities are not seen in healthy children with Down syndrome.
In adults with Down syndrome who develop Alzheimer disease (also characterized by long-tract signs), these signs have less clinical value.
Torticollis may be a presenting sign. The diagnosis of torticollis in a person with Down syndrome indicates AAI until proven otherwise.
Causes
Many genetic and congenital developmental abnormalities affect the craniocervical junction.28, 1, 26, 29, 30, 17
In the case of persons with Down syndrome, congenital absence or laxity of the transverse atlas ligament (which may be associated with congenital anomalies of the odontoid bone) must be considered. This is not proven to cause AAI.15, 7
When this abnormality is present, trivial trauma to the cervical area or acute infections of the nasopharyngeal area also may produce subluxation.9
Lymphatic drainage of this area is the same as that of the cervico-occipital junction, and retrograde infections may play a role in the instability of the craniocervical joint.9 The syndrome has been described after infections or surgical procedures (eg, mastoidectomies, tonsillectomies) in the mastoid, middle ear, and tonsils.15
Some pure cases of AAI are associated with degenerative arthritis or rheumatoid arthritis of the cervical spine.31
Other diagnostic considerations
Any pathology in the upper cervical spine can mimic symptoms of AAI.
Adults with Down syndrome frequently develop Alzheimer disease. This disorder is associated with long-tract signs that may mask or mimic spinal cord compression.10
Hypothyroidism is frequent in individuals with Down syndrome and may play a role in this condition or be a separate cause of behavioral changes.14
Degenerative disease of the cervical spine is common in individuals with Down syndrome.17 Subluxation may occur at multiple levels.19
Posterior atlanto-occipital subluxation with or without AAI has been described, including malformations of the odontoid bone, intervertebral disk abnormalities, and changes at the base of the skull.
Differential Diagnoses
Alzheimer Disease
Spinal Cord Infarction
Alzheimer Disease in Individuals With Down Syndrome
Spinal Epidural Abscess
Ankylosing Spondylitis
Torticollis
Ataxia with Identified Genetic and Biochemical Defects
Vitamin B-12 Associated Neurological Diseases
Mental Retardation
Spinal Cord Hemorrhage
Other Problems to Be Considered
Brainstem syndromesCervical disk syndromes
Workup
Laboratory Studies
No specific lab studies are indicated in atlantoaxial instability (AAI).
Given the high frequency of hypothyroidism in individuals with Down syndrome, a full thyroid workup may be indicated.
Imaging Studies
Neuroimaging studies of the cervical spine are the most important diagnostic tests.12, 32
Lateral radiographs of the cervical spine in 3 positions (flexion, neutral, and extension) are used for screening purposes.6 A conservative approach consists of obtaining cervical radiographs in every child with Down syndrome, usually in early childhood, and always before the child is involved in physical activities.33 However, others do not agree with the need to perform regular radiologic screening evaluation.8, 15
Lateral radiographs of the neck are recommended by the Special Olympics Committee and were endorsed by the AmericanAcademy of Pediatrics34; however, later, the AmericanAcademy of Pediatrics changed its position.34 This resulted in heated arguments among experts in the fields11 and editorial reviews.14 At the present time this issue is not fully resolved. National protocols have not been established and the recommendations regarding screening varies from state to state29 and from country to country. For example, routine screening is not recommended in the United Kingdom.35
A longitudinal, clinical, and radiologic follow-up of 127 adults with Down syndrome in whom periodic cervical radiographs were obtained, showed that the atlanto-odontoid junction remained stable with no significant radiologic changes in most of these individuals. The individuals' average age at the time of the first set of radiographs was 38 years, with a range of 18-67 years, and an average age at the time of the last set of radiographs of 43 years, with a range of 23-67 years. In addition, when radiologic changes were observed, they were of no clinical significance. This study suggests that in the absence of clinical indications, repeat cervical radiographs are not needed in asymptomatic adults with Down syndrome.(AN unpublished information, 2004).
In most individuals with symptomatic AAI, the neurologic signs develop slowly, in a matter of weeks, so a neurologic examination before sport activities might be more predictive of AAI than radiologic screening.15
The usefulness of the lateral cervical radiographs in asymptomatic children have not been fully resolved. Until more evidence-based information is available, the author recommends obtaining lateral cervical radiographs around the age of 4-5 years in asymptomatic children with Down syndrome. Those with radiologic indications of AAI should be closely observed by a clinician expert in the early subtle signs of this condition. In these individuals, the parents should be educated in the early recognition of early signs of complicated AAI.
In cooperative individuals, an open-mouth view of the upper cervical spine can assess the odontoid bone.
Normally, neck flexion shows minimal separation between the odontoid and the atlas (anterior atlanto-odontoid distance [AAOD]). This separation should be less than 3 mm (see Media file 1).11 In children younger than 15 years, up to 4 mm can be considered normal.6, 36, 37 An AAOD between 3-5 mm is borderline, and distances of more than 6 mm are considered suggestive of AAI (see Media files 2-5).
Of asymptomatic children with Down syndrome, 17% have an AAOD greater than 5 mm.
Measures of the posterior atlanto-odontoid distance (PAOD), which better correlate with the neural canal width, might have more clinical relevance than the measurements of the AAOD. Values of PAOD less than 12-13 mm are usually associated with clinical symptoms.
Computed tomography (CT) and magnetic resonance imaging (MRI) are the best neuroradiologic tests to view the various structures of the cervical spine.16 Superior to CT scan for evaluating the spinal cord, MRI should be used when spinal cord compression is suspected. However, CT scans are useful as an adjunct to the MRI for evaluation of bony abnormalities.
These tests are indicated in all patients who show some clinical symptoms suggesting complications of AAI. They are optional in asymptomatic individuals when the cervical spine plain radiograph reveals subluxation of greater than 5 mm. These studies are not indicated for routine screening.
Myelogram is rarely indicated since MRI resolution is sufficient in most clinical situations.
Treatment
Medical Care
Medical (ie, nonsurgical) care is primarily symptomatic to treat pain or discomfort.
A cervical collar and traction can be tried, but if the clinical symptoms do not improve, surgical treatment is indicated.5, 6
A hard cervical collar might be needed after C1-C2 surgical fixation.6
Surgical Care
The preferred surgical option, in the presence of symptoms, is fusion of C1 to C2.6
Other options have been explored but have been less effective.
Surgery is more effective in individuals whose AAI has been diagnosed recently. In those with long-standing symptoms, surgery may prevent further deterioration, but chronic symptoms do not improve significantly.11
Fusion of the cervical spine is not complication free. In some cases, the clinical situation deteriorates after surgery.6
The C1-C2 fusion might lead to instability of the atlanto-occipital joint.38
Consultations
Consider consultation with a neurologist when the symptoms suggest AAI and diagnostic workup is needed. Neurosurgery or orthopedics should be consulted when surgery is being considered.
Red flags
Neck pain
New onset of gait impairment
Torticollis
Any indication of motor difficulties in the upper or lower extremities
Diet
No particular diet is recommended.
Activity
In individuals with radiologic evidence of AAI without clinical signs or symptoms, activities that might produce injury to the cervical spine should be restricted.
Without evidence of subluxation, physical activity restriction is unnecessary.
Symptomatic individuals need full restriction of physical activities until surgery is performed.
[Section on medication removed for purposes of brevity]
Presurgical care
In most instances, these patients do not need emergency surgery. The presurgical care is, in general, not different from the care needed for persons who do not have mental retardation.
Some factors to be considered: Persons with Down syndrome have a higher incidence of congenital cardiac conditions, hepatitis, and hypothyroidism, and should be evaluated for these conditions before surgery. Emotional and behavioral issues could be complicating factors, mostly in the postoperative period. Explaining the inconveniences associated with major surgery to people with developmental disabilities is always difficult.
Postsurgical care
Pain should be expected in the postoperative period. In most instances, because of their mental retardation, patients are not able to verbalize their pain, and behavioral changes might be the only indication of pain.
Companionship at the bedside is important for these patients. The physician should arrange for this companionship. The ideal situation is to have someone at the bedside 24 h/d, preferably persons who know the patient well.
Patients might need to be in bed for many days after the surgery, and deep vein thrombosis (DVT) may be a complication during this period. The caretakers should be instructed in prevention of DVT, such as moving the patient in bed and performing passive exercises of the legs. The rehabilitation should be started as soon as possible. Patients should be encouraged to move, even when in bed.
Complications of the surgery, such as postoperative bleeding in the cervical spine, might result in compression of the upper cervical cord. This could lead to motor paralysis that might be very difficult to diagnose in the early stages. In extreme cases, respiratory depression might be a complication.
In most instances, a cervical collar is used to stabilize the surgical area. Since most of the patients have some degree of mental retardation, implementation of a cervical collar might require some sedation.
Further Outpatient Care
In children who have atlanto-odontoid distance (AAOD) of 3 mm or less, repeating the cervical radiograph is probably unnecessary.
These children need clinical follow-up only.
Neuroimaging should be pursued only if new neurologic signs arise.
No protocol exists for children with AAOD of 3-5 mm.
Clinical follow-up and restricting activities that may traumatize the cervical spine (eg, somersaults, contact sports, trampoline exercises) may be all that is needed.
Consider repeating the cervical radiograph in 1-2 years.
In patients in whom the AAOD is greater than 5 mm, a more complete evaluation with a cervical MRI is recommended. This also applies for children whose PAOD is less than 12 mm.
Individuals with radiologic evidence of AAI but no symptoms should have at least a yearly clinical evaluation. Immediate reevaluation is needed if they present with new symptoms.
Only a small percentage of children with radiologic evidence of AAI will become symptomatic.
The symptoms are often insidious.
Quadriplegia is reported occasionally (but rarely) as an initial symptom.
Clinical deterioration can be observed after minimal trauma or after acute pharyngeal infections.
Inpatient & Outpatient Medications
Analgesics for pain
Transfer
Patients are likely to remain in the hospital for at least 1 week, since sending these patients home is difficult; they might require transfer to a rehabilitation hospital.
The average stay at the rehabilitation hospital is 1 month.
Nursing homes should be avoided since they are usually not equipped for patients with Down syndrome.
Complications
The main complication is spinal cord compression.
Root compression in the cervical area might be associated with posterior neck and occipital pain.
Torticollis may be a sign of subluxation.
Prognosis
AAI does not usually produce clinical symptoms.
In symptomatic individuals, treatment in the acute phase may reverse the symptoms.
In long-standing cases, the surgical procedure is not associated with clinical improvement.
Patient Education
Explain the following to parents and/or legal guardians:
Potential problems that could occur
The need to impose certain limitations and restrictions
The associated ethical issues
Miscellaneous
Medicolegal Pitfalls
The early symptoms of subluxation are often subjective and difficult to elucidate in patients with mental retardation. This may result in a delay of diagnosis.
Suspect atlantoaxial instability (AAI) in an individual with Down syndrome who presents with decreased motor skills or who develops torticollis, a gait disorder, or any form of progressive paralysis.
Although the compression is in the high cervical spine, the first motor symptoms or signs may be discovered in the legs.
Special Concerns
Manipulation of the cervical spine is always dangerous in individuals with Down syndrome (even those who are asymptomatic).
Relaxation during anesthesia might allow extreme movements of the cervical spine. This should be a concern in any person with Down syndrome who needs general anesthesia; however, children with normal radiographic studies of the cervical spine can tolerate flexion and extension of the cervical spine during anesthesia.39
Prior to elective intubations, a cervical spine radiograph series should be performed. Fiberoptic intubation may be desirable in patients with Down syndrome to avoid overmanipulation of the neck.
Emergency intubation of people with Down syndrome should be performed with extreme care and minimal manipulation of the neck, mostly if the condition of the AAI is unknown.
Physical activities that result in trauma to the cervical spine should be avoided.
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Keywords
atlantoaxial instability, Down syndrome, atlantooccipital joints, atlanto-occipital joints, occipitocervical articulation, AAI, DS, brainstem syndrome
Contributor Information and Disclosures
Author
Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's HospitalNorberto Alvarez, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society, and Child Neurology SocietyDisclosure: Nothing to disclose
Medical Editor
Michael J Schneck, MD, Associate Professor, Departments of Neurology and Neurosurgery, Stritch School of Medicine, Loyola University; Associate Director, Stroke Program, Director, Neurology Intensive Care Program, Medical Director, Neurosciences ICU, Loyola University Medical CenterMichael J Schneck, MD is a member of the following medical societies: American Academy of Neurology, American Society of Neuroimaging, Neurocritical Care Society, and Stroke Council of the American Heart AssociationDisclosure: boehringer-ingelheim Honoraria for Speaking and teaching; sanofi/bms Honoraria for Speaking and teaching; pfizer Honoraria for Speaking and teaching; genentech Honoraria for Speaking and teaching; ucb pharma Honoraria for Speaking and teaching; talecris Consulting fee for Other; nmt medical Grant/research funds for Independent contractor; NIH Grant/research funds for Independent contractor; vernalis Grant/research funds for Independent contractor; sanofi Grant/research funds for Independent contractor; boehringer-ingelheim Grant/research funds for Independent contractor; photophera inc Grant/research funds for Independent contractor
Pharmacy Editor
Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicineDisclosure: Nothing to disclose
Managing Editor
Kenneth J Mack, MD, PhD, Senior Associate Consultant, Department of Child and Adolescent Neurology, Mayo ClinicKenneth J Mack, MD, PhD is a member of the following medical societies: American Academy of Neurology, Child Neurology Society, Phi Beta Kappa, and Society for NeuroscienceDisclosure: Nothing to disclose
CME Editor
Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community HospitalMatthew J Baker, MD is a member of the following medical societies: American Academy of NeurologyDisclosure: Nothing to disclose
Chief Editor
Amy Kao, MD, Assistant Professor, Department of Neurology, Division of Pediatrics, Department of Pediatrics, Oregon Health and Science University; Consulting Staff, Shriners Hospital for ChildrenAmy Kao, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, American Epilepsy Society, and Child Neurology SocietyDisclosure: Nothing to disclose
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