Sacroilitis Differential Diagnosis

The differential diagnosis for sacroilitis can be organized into the following categories:

• Single Most Likely Diagnosis

  • Ankylosing Spondylitis (AS): This is a form of arthritis that primarily affects the spine, although other joints can also be involved. It causes inflammation of the spinal joints (vertebrae) that can lead to severe, chronic pain and discomfort. Sacroilitis is a hallmark of AS, making it the single most likely diagnosis for patients presenting with sacroilitis symptoms.

• Other Likely Diagnoses

  • Psoriatic Arthritis (PsA): This condition occurs in some people with psoriasis, causing joint pain, stiffness, and swelling. Sacroilitis can be a feature of PsA, especially in those with significant axial involvement.
  • Reactive Arthritis: Previously known as Reiter's syndrome, this form of arthritis occurs as a reaction to an infection elsewhere in the body, often in the gastrointestinal tract or the urinary tract. It can cause sacroilitis among other symptoms like conjunctivitis and urethritis.
  • Enteropathic Arthritis: Associated with inflammatory bowel diseases like Crohn's disease and ulcerative colitis, this condition can lead to sacroilitis due to the systemic inflammation affecting the sacroiliac joints.

• Do Not Miss Diagnoses

  • Infectious Sacroilitis: Caused by bacterial, fungal, or parasitic infections, this condition can lead to severe complications if not promptly treated. It's crucial to consider this diagnosis, especially in patients with risk factors for infections or those who are immunocompromised.
  • Osteonecrosis of the Sacrum: Although rare, this condition involves the death of bone tissue due to a lack of blood supply and can mimic sacroilitis in its presentation. It's a critical diagnosis not to miss due to its potential for significant morbidity.
  • Sacral Insufficiency Fracture: Often occurring in patients with osteoporosis or those on long-term corticosteroid therapy, these fractures can present with sacroilitis-like symptoms and are essential to diagnose to prevent further bone weakening and potential neurological complications.

• Rare Diagnoses

  • Brucellosis: A zoonotic infection that can cause sacroilitis among other systemic symptoms. It's rare in many parts of the world but should be considered in individuals with exposure to infected animals or their products.
  • Sarcoidosis: A condition characterized by the growth of granulomas (inflammatory cells) in various parts of the body, which can rarely affect the sacroiliac joints and mimic sacroilitis.
  • Eosinophilic Granuloma: Part of the spectrum of Langerhans cell histiocytosis, this condition can rarely involve the sacrum and present with sacroilitis-like symptoms.