Differential Diagnosis for Bilateral Sacroillitis and Quantiferon Positive
Single Most Likely Diagnosis
- Ankylosing Spondylitis (AS): This is the most likely diagnosis given the presence of bilateral sacroillitis, which is a hallmark of AS. The Quantiferon positive result suggests latent tuberculosis infection, but this can be seen in AS patients, especially if they are from endemic areas or have been exposed to TB. AS is a type of spondyloarthritis that primarily affects the spine and sacroiliac joints.
Other Likely Diagnoses
- Reactive Arthritis: This condition can also present with sacroillitis and is often triggered by a bacterial infection. A Quantiferon positive result could be incidental, but it's essential to consider reactive arthritis, especially if there's a history of recent infection.
- Psoriatic Arthritis: Although less commonly associated with bilateral sacroillitis compared to AS, psoriatic arthritis can present with sacroiliac joint involvement and should be considered, especially in patients with psoriasis or a family history of psoriasis.
- Enteropathic Arthritis: Associated with inflammatory bowel diseases like Crohn's disease and ulcerative colitis, enteropathic arthritis can cause sacroillitis. The Quantiferon positive result would need to be considered in the context of the patient's overall clinical picture.
Do Not Miss Diagnoses
- Tuberculosis (TB) of the Sacroiliac Joint: Although less common, TB can infect the sacroiliac joints, causing sacroillitis. Given the Quantiferon positive result, it's crucial to rule out active TB, especially if the patient has risk factors for TB or symptoms suggestive of active infection.
- Sarcoidosis: This systemic disease can cause sacroillitis and might also result in a false-positive Quantiferon test due to its impact on the immune system. Sarcoidosis affecting the musculoskeletal system is less common but should be considered to avoid missing this diagnosis.
Rare Diagnoses
- Brucellosis: This zoonotic infection can cause sacroillitis among other symptoms. It's rare in many parts of the world but should be considered in patients with exposure history (e.g., contact with infected animals).
- Osteonecrosis of the Sacroiliac Joint: Although not typically associated with a Quantiferon positive result, osteonecrosis can cause sacroiliac joint pain and might mimic sacroillitis in imaging studies. It's a rare condition but should be considered in the differential diagnosis, especially in patients with risk factors for osteonecrosis.