What is the appropriate management for a patient with increased signaling on MRI imaging indicative of bone marrow changes, potentially due to traumatic injury or inflammatory conditions such as sacroiliac joint inflammation in axial spondyloarthritis?

Management of Increased MRI Signal with Bone Marrow Changes

Bone marrow edema on MRI is a nonspecific finding that demands immediate clinical correlation to distinguish benign self-limited conditions from serious pathology requiring urgent intervention, including osteonecrosis, insufficiency fractures, inflammatory arthritis, infection, or malignancy. 1

Initial Diagnostic Approach

Essential Imaging Protocol

• Always obtain both STIR (or T2-weighted) and T1-weighted sequences—never interpret STIR hyperintensities in isolation. 2, 3 This combined approach differentiates acute inflammatory changes (bright on STIR, variable on T1) from chronic structural changes (abnormal on T1, variable on STIR).

• For sacroiliac joint evaluation specifically, interrogation using both STIR and T1-weighted images is critical to identify both inflammatory and structural changes of axial spondyloarthritis. 2

Clinical Context Integration

The same MRI finding has vastly different implications depending on patient characteristics: 1, 4

• Deep bone marrow edema extending ≥1 cm from the articular surface is highly specific for pathologic inflammation, found almost exclusively in axial spondyloarthritis. 2 This distinguishes true inflammatory disease from physiologic variants.

• Bone marrow edema in healthy athletes, postpartum patients, or up to 30% of healthy controls may be physiologic and benign. 2, 4

• In middle-aged to elderly patients with acute pain, suspect subchondral insufficiency fracture—MRI detects these before radiographs become abnormal. 1, 4

Critical Differential Diagnoses to Rule Out

High-Priority Conditions Requiring Urgent Action

1. Inflammatory Arthritis (Axial Spondyloarthritis)

• Look for bone marrow edema combined with synovitis and joint effusion—this combination indicates inflammatory disease requiring disease-modifying therapy, not just symptomatic treatment. 1, 4
• The ASAS definition of positive MRI (bone marrow edema alone) has sensitivity 79% and specificity 89% for axial spondyloarthritis. 2
• However, combining erosions and/or bone marrow edema increases both sensitivity (90-92%) and specificity (94-97%) compared to bone marrow edema alone. 2
• Additional highly specific findings (95-98% specificity): subchondral fatty deposition, intra-articular T1 hyperintensity, T2 hyperintense joint fluid, and ankylosis. 2

2. Osteonecrosis

• Bone marrow edema surrounding a focus of necrosis, particularly with joint effusion, increases risk for femoral head collapse. 1
• Use dynamic contrast-enhanced MRI to differentiate: osteonecrosis shows a rim of high plasma flow surrounding a subchondral area without flow, whereas transient bone marrow edema syndrome shows subchondral hyperperfusion. 1
• Osteonecrosis demonstrates overall decreased maximal enhancement compared to transient bone marrow edema or subchondral insufficiency fracture. 1

3. Subchondral Insufficiency Fracture

• Most commonly affects the medial femoral condyle in middle-aged to elderly females. 1, 4
• Can progress to articular collapse requiring arthroplasty if untreated—rule this out early. 1, 4
• MRI identifies these before radiographs show abnormalities. 1, 4

4. Osteomyelitis

• Causes bone marrow edema with increased signal on T2 and STIR sequences. 1
• High bone marrow signal on STIR combined with low signal on T1-weighted images suggests osteomyelitis (sensitivity ~90%, specificity ~85%). 3
• In diabetic patients with Charcot arthropathy, bone marrow edema is difficult to distinguish from superimposed osteomyelitis—delayed multidisciplinary referral leads to significant clinical deterioration. 1, 4
• MRI is exceptional for detecting acute osteomyelitis, though detecting acute changes in chronic post-traumatic osteomyelitis is challenging due to marrow signal heterogeneity from prior trauma or surgery. 2

5. Malignancy

• Consider bone marrow biopsy when diffuse signal alterations are detected incidentally—one retrospective study found clinically important hematological disorders in 47% of patients who underwent biopsy for incidental diffuse bone marrow signal changes. 5

Treatment Algorithm Based on Etiology

For Inflammatory Arthritis (Axial Spondyloarthritis)

• First-line: Physical therapy and NSAIDs, though less than 25% achieve complete symptom control with NSAIDs alone. 6
• Approximately 75% of patients require biologic drugs (anti-TNF agents, anti-IL-17 agents) or JAK inhibitors. 6
• Anti-TNF agents achieve ASAS20 improvement in 58-64% (vs 19-38% placebo), anti-IL-17 agents in 48-61% (vs 18-29% placebo), and JAK inhibitors in 52-56% (vs 26-29% placebo). 6

For Transient Bone Marrow Edema Syndrome

• Iloprost infusion: 50 μg intravenously over 6 hours daily for 5 consecutive days. 4
• This idiopathic, self-limiting condition shows diffuse bone marrow edema throughout the femoral head and neck without the characteristic rim sign of osteonecrosis. 1

For Traumatic/Mechanical Causes

• Protected weight-bearing with immobilization using total contact casting or non-removable knee-high devices for 6-12 weeks. 4
• Custom footwear with specialized insoles after the acute phase to prevent recurrence. 4

Critical Pitfalls to Avoid

1. Do not assume all bone marrow edema is benign. New or increasing edema correlates with pain progression and can lead to joint destruction if the underlying cause is not addressed. 1, 4

2. Do not rely solely on bone marrow edema for diagnosing axial spondyloarthritis. The ASAS MRI criteria have been criticized for decreased specificity when using bone marrow edema as the sole diagnostic criterion, as it can be seen in age-related degenerative changes, postpartum patients, chronic back pain, and athletes. 2

3. Do not ignore structural changes on T1-weighted images. Erosions, sclerosis, fatty deposition, and ankylosis are not accounted for in the ASAS definition of positive MRI but are important findings that should be identified in clinical practice. 2

4. Do not delay diagnosis in diabetic patients. Prompt multidisciplinary referral is essential to prevent significant clinical deterioration in Charcot arthropathy. 1, 4

5. Monitor for progression of subchondral insufficiency fractures, which can progress to articular fragmentation and collapse, particularly in the medial femoral condyle. 1, 4