Differential Diagnosis for Atlantoaxial Instability

A patient presenting with atlantoaxial instability may have a variety of underlying causes. The differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Rheumatoid Arthritis: This is a common cause of atlantoaxial instability due to the inflammatory nature of the disease, which can lead to erosion of the ligaments and bones in the cervical spine, particularly at the atlantoaxial joint.

• Other Likely Diagnoses

  • Trauma: Acute injuries to the neck can cause atlantoaxial instability, either through fractures or ligamentous injuries.
  • Congenital Conditions: Certain congenital conditions, such as Down syndrome or Klippel-Feil syndrome, can increase the risk of atlantoaxial instability due to anatomical abnormalities.
  • Infectious Diseases: Infections like osteomyelitis or discitis can weaken the spinal structures and lead to instability.
  • Degenerative Conditions: Degenerative changes, such as those seen in osteoarthritis, can also contribute to atlantoaxial instability over time.

• Do Not Miss Diagnoses

  • Odontoid Fracture: Although this might seem like an obvious diagnosis, missing it could be catastrophic. An odontoid fracture can lead to acute instability and requires immediate attention.
  • Spinal Cord Injury: Any condition that compromises the spinal cord, such as a herniated disc or spinal stenosis, in the context of atlantoaxial instability, is critical and must not be missed.
  • Meningitis or Abscess: Infections that involve the meninges or form abscesses near the atlantoaxial joint can present with instability and are medical emergencies.

• Rare Diagnoses

  • Pseudogout: Calcium pyrophosphate deposition disease (CPPD) can rarely cause atlantoaxial instability by depositing crystals in the joint, leading to inflammation and structural damage.
  • Gout: Similar to pseudogout, gout can cause inflammatory arthritis that affects the atlantoaxial joint, although this is less common.
  • Neoplastic Conditions: Tumors, either primary or metastatic, can weaken the bones and ligaments of the cervical spine, leading to instability.
  • Spondyloarthropathies: Conditions like ankylosing spondylitis can lead to atlantoaxial instability, although this is less common compared to other causes.

Each of these diagnoses has a different set of implications for treatment and management, emphasizing the importance of a thorough diagnostic workup for patients presenting with atlantoaxial instability.