Crowned Dens Syndrome Mimicking Atlantoaxial Infection in a Patient With Systemic Sclerosis: A Case Report.

Crowned dens syndrome (CDS), caused by calcium pyrophosphate or hydroxyapatite deposition around the odontoid process, is an under-recognized cause of acute severe neck pain and headache. It can closely mimic septic arthritis, osteomyelitis, giant cell arteritis (GCA), polymyalgia rheumatica (PMR), or cervical spondylitis. We report a case of CDS in a patient with diffuse systemic sclerosis initially managed for presumed infection. A 55-year-old man with diffuse cutaneous systemic sclerosis on mycophenolate mofetil and methotrexate presented with severe throbbing headache, facial tenderness, and diffuse pain. CT/CTA of the head and neck were negative for vascular events; MRI revealed inflammatory changes at the atlantoaxial and atlanto-occipital joints concerning for septic arthritis/osteomyelitis with abscess formation. Broad-spectrum antibiotics were initiated. The patient's symptoms persisted despite antibiotics, prompting repeat imaging. CT demonstrated calcifications surrounding the odontoid process, raising suspicion for CDS. Colchicine and low-dose prednisone were introduced while antibiotics were continued, given ongoing concern for occult infection in an immunosuppressed host. Within 1 week, the patient experienced near-complete resolution of pain. At follow-up, he remained symptom-free, allowing reintroduction of methotrexate while mycophenolate was held. CDS should be considered in the differential diagnosis of severe headache and neck pain in rheumatology patients, particularly when imaging shows craniocervical inflammation and calcifications. CT of the odontoid is diagnostic, but MRI findings may mimic infection. Awareness of CDS is critical to avoid misdiagnosis, unnecessary procedures, or prolonged inappropriate therapy. Prompt recognition and anti-inflammatory treatment can be rapidly effective and permit safe reintroduction of disease-modifying therapy.