A 22-year-old woman complains of unilateral low back and buttock pain for 4 months with a limp. There is tenderness over the left sacroiliac joint and the FABER test reproduces her pain. MRI shows erosions of both the sacral and iliac surfaces of the left sacroiliac joint with a small adjacent soft tissue collection. The most likely diagnosis is:

• A Tuberculous sacroiliitis ✓
• B Ankylosing spondylitis
• C Acute pyogenic sacroiliitis
• D Osteitis condensans ilii

Explanation

Unilateral sacroiliac joint involvement with erosions of both articular surfaces, an indolent course over months, and an adjacent soft tissue collection is typical of tuberculosis, which reaches the joint by contiguous spread from the adjacent ilium or sacrum. Ankylosing spondylitis produces bilateral symmetric sacroiliitis with subchondral sclerosis rather than collections. Pyogenic sacroiliitis presents acutely with high fever and severe pain over days to weeks, inconsistent with this 4-month history.

Reference: Tuli's Tuberculosis of the Skeletal System, 5th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.