Differential Diagnosis for Sacroilitis with HLA-B27 Negative Cause

Single Most Likely Diagnosis

• Osteitis Condensans Ilii: A self-limiting, non-inflammatory condition that can mimic sacroilitis on imaging, often seen in postpartum women or those with a history of trauma. The HLA-B27 negative status and absence of systemic symptoms make this a plausible diagnosis.

Other Likely Diagnoses

• Psoriatic Arthritis: Although often associated with HLA-B27, psoriatic arthritis can occur in HLA-B27 negative individuals. The presence of psoriatic skin lesions or nail changes would support this diagnosis.
• Reactive Arthritis: Typically follows a gastrointestinal or genitourinary infection, and while it's more common in HLA-B27 positive individuals, it can occur in those who are HLA-B27 negative.
• Inflammatory Bowel Disease (IBD)-associated Arthritis: Both Crohn's disease and ulcerative colitis can cause sacroilitis, regardless of HLA-B27 status. A history of gastrointestinal symptoms or a family history of IBD would increase the likelihood of this diagnosis.

Do Not Miss Diagnoses

• Infectious Sacroilitis: Caused by bacteria (e.g., Staphylococcus aureus, Salmonella), fungi, or parasites. This diagnosis is critical to consider due to the potential for severe consequences if left untreated, including sepsis or chronic infection.
• Tuberculous Sacroilitis: A rare but serious condition that requires prompt diagnosis and treatment to prevent long-term disability or spread of the infection.

Rare Diagnoses

• Brucellar Sacroilitis: A zoonotic infection that can cause sacroilitis, more common in individuals who work with animals or consume unpasteurized dairy products.
• Sarcoidosis: A systemic granulomatous disease that can rarely cause sacroilitis, typically in the context of other systemic symptoms or findings.
• Ehlers-Danlos Syndrome: A group of genetic disorders affecting connective tissue, which can lead to sacroilitis due to joint hypermobility and instability.