American Board of Internal Medicine (ABIM) Certification Practice Exam

What imaging modality should be used to evaluate for osteonecrosis in lupus patients when plain radiographs are normal?

1. CT scan

2. Ultrasound

3. MRI

4. X-ray

The correct answer is: MRI

MRI is the preferred imaging modality for evaluating osteonecrosis, especially in patients with systemic lupus erythematosus (SLE) when plain radiographs are normal. This is because MRI is highly sensitive in detecting early changes due to osteonecrosis, including bone marrow edema and microfractures, which may not be visible on plain X-rays until later stages of the disease when structural changes have occurred. Osteonecrosis in lupus patients is a significant concern, often related to corticosteroid use or disease-related vascular complications. Since the condition can develop insidiously and go unnoticed in its early stages, MRI can identify abnormalities much sooner than other imaging modalities. While CT scans can also provide detailed images of bones, they are less sensitive than MRI for detecting early osteonecrosis. Ultrasound does not offer the same level of detail for evaluating bone structures and is mainly used for soft tissue assessment. Plain X-rays, while useful in assessing joint and bone structure, often miss early signs of osteonecrosis, which is why they are inadequate when normal. In summary, the superior sensitivity and ability to visualize early pathological changes in bone marrow make MRI the best choice for evaluating osteonecrosis in lupus patients when other imaging findings are unremarkable.