eMedicine Specialties > Neurology > Pediatric Neurology

Atlantoaxial Instability in Individuals with Down Syndrome

Author: Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital
Contributor Information and Disclosures

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.

More on Atlantoaxial Instability in Individuals with Down Syndrome

Overview: Atlantoaxial Instability in Individuals with Down Syndrome
Differential Diagnoses & Workup: Atlantoaxial Instability in Individuals with Down Syndrome
Treatment & Medication: Atlantoaxial Instability in Individuals with Down Syndrome
Follow-up: Atlantoaxial Instability in Individuals with Down Syndrome
Multimedia: Atlantoaxial Instability in Individuals with Down Syndrome
References
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References

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Further Reading

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Keywords

atlantoaxial instability, Down syndrome, atlantooccipital joints, atlanto-occipital joints, occipitocervical articulation, AAI, DS, brainstem syndrome

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Contributor Information and Disclosures

Author

Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital
Norberto Alvarez, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society, and Child Neurology Society
Disclosure: 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 Center
Michael 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 Association
Disclosure: boehringer-ingelheim Honoraria Speaking and teaching; sanofi/bms Honoraria Speaking and teaching; pfizer Honoraria Speaking and teaching; genentech Honoraria Speaking and teaching; ucb pharma Honoraria Speaking and teaching; talecris Consulting fee Other; nmt medical  Independent contractor; NIH Grant/research funds Independent contractor; vernalis Grant/research funds Independent contractor; sanofi Grant/research funds Independent contractor

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Kenneth J Mack, MD, PhD, Senior Associate Consultant, Department of Child and Adolescent Neurology, Mayo Clinic
Kenneth 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 Neuroscience
Disclosure: Nothing to disclose.

CME Editor

Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital
Matthew J Baker, MD is a member of the following medical societies: American Academy of Neurology
Disclosure: 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 Children
Amy Kao, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Pediatrics, American Epilepsy Society, and Child Neurology Society
Disclosure: Nothing to disclose.

 
 
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