Differential Diagnosis for Syndesmophytes and Fusion of SI Joint
- Single most likely diagnosis
- Ankylosing Spondylitis (AS): This is the most likely diagnosis due to the presence of syndesmophytes, which are a hallmark of AS, and fusion of the SI joint, which is a common feature of advanced AS. AS is a chronic inflammatory disease that primarily affects the spine and SI joints.
- Other Likely diagnoses
- Psoriatic Arthritis (PsA): PsA can also cause syndesmophytes and SI joint fusion, although it is less common than in AS. The presence of psoriatic skin lesions or nail changes would support this diagnosis.
- Reactive Arthritis: This condition can cause SI joint inflammation and fusion, although syndesmophytes are less common. A history of recent gastrointestinal or genitourinary infection would be consistent with reactive arthritis.
- Enteropathic Arthritis: This condition is associated with inflammatory bowel disease (IBD) and can cause SI joint inflammation and fusion, as well as syndesmophytes.
- Do Not Miss diagnoses
- Infectious Spondylitis: Although less likely, infectious spondylitis (e.g., tuberculous or pyogenic) can cause SI joint destruction and fusion. A history of fever, night sweats, or recent travel to an endemic area would raise suspicion for this diagnosis.
- Osteonecrosis of the SI Joint: This condition can cause SI joint destruction and fusion, although it is less common. A history of corticosteroid use or trauma would support this diagnosis.
- Rare diagnoses
- Spondyloarthritis associated with Inflammatory Bowel Disease (IBD): This condition is rare, but can cause SI joint inflammation and fusion, as well as syndesmophytes.
- Chronic Recurrent Multifocal Osteomyelitis (CRMO): This rare condition can cause SI joint inflammation and fusion, although it is more commonly seen in children and adolescents.
- Ochronotic Arthropathy: This rare condition is caused by alkaptonuria and can lead to SI joint fusion and syndesmophytes, although it is extremely rare.