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Radiology · Musculoskeletal imaging: early sacroiliitis
Sample itemA 24-year-old man has inflammatory back pain for four months with normal sacroiliac joint radiographs. Which investigation can show the earliest changes of sacroiliitis?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
C. MRI with STIR sequences
MRI with fat-suppressed STIR sequences shows bone marrow oedema, the earliest sign of active sacroiliitis, years before radiographic erosions. Radiographs show later changes such as erosions and sclerosis. Bone scans lack specificity and ultrasound cannot image the deep joint.
Option by option
A. Repeat plain radiograph at six weeks
Repeating the plain film would remain normal until structural damage develops.
B. Ultrasound of the sacroiliac joint
Ultrasound cannot evaluate the deep synovial and cartilaginous joint.
C. MRI with STIR sequences (correct)
Correct. STIR MRI reveals marrow oedema before structural change appears on radiographs.
D. Technetium bone scan with SPECT
Bone scintigraphy is non-specific and poorly sensitive for early sacroiliitis.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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