A 55-year-old woman with rheumatoid arthritis on methotrexate and hydroxychloroquine presents with bilateral lower limb weakness, loss of sensation below T6, and bladder dysfunction developing over 2 days. MRI spine shows cervical cord compression at C3–C4. Neurological examination reveals hyperreflexia. What is the most likely structural cause of her myelopathy?

• A Methotrexate-induced spinal cord toxicity
• B Rheumatoid pannus causing atlantoaxial subluxation ✓
• C Transverse myelitis from associated lupus
• D Pathological fracture from osteoporosis

Explanation

Atlantoaxial subluxation (C1–C2 instability) is the most dreaded cervical spine complication of rheumatoid arthritis, caused by synovitis and pannus formation eroding the transverse ligament of the atlas and the dens. It results in anterior subluxation of C1 on C2, compressing the cervical spinal cord and causing myelopathy. All RA patients should have pre-operative lateral flexion-extension cervical X-rays to screen for this. The absence of odontoid peg visualized on imaging is a key radiological clue. Surgical stabilization is required.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.