What are the typical radiological findings in chronic recurrent multifocal osteomyelitis (CRMO)?

Radiological Findings in CRMO

CRMO demonstrates characteristic multifocal bone lesions with a predilection for metaphyseal regions of long bones (particularly tibia and femur), clavicles, and spine, appearing as mixed lytic-sclerotic lesions with hyperostosis and periosteal reaction on radiographs, while whole-body MRI reveals the full extent of disease including subclinical lesions.

Key Imaging Characteristics by Modality

Plain Radiography

The initial imaging findings on plain radiographs include 1, 2:

• Mixed lytic and sclerotic lesions (most common appearance)
• Hyperostosis or periosteal thickening - particularly prominent in long bones
• Metaphyseal or juxta-physeal location in long bones
• Bone sclerosis with areas of destruction in chronic cases

Important caveat: Plain radiography lacks sensitivity early in disease and may be completely normal initially, but remains essential for initial screening and monitoring lesion progression 3.

MRI Findings (Preferred Modality)

MRI, particularly whole-body MRI with sagittal spinal images, should be the primary imaging modality 4. Key findings include 5:

Long bone involvement (65% metaphyseal, 35% epiphyseal):

• Distal metaphyseal lesions (42% of metaphyseal lesions)
• Peri-physeal involvement (173 lesions in one study)
• Metaphyseal lesions tend to be extensive (75%), while epiphyseal lesions are minimal (60%)
• Bone marrow edema on STIR/T2-weighted sequences
• Soft-tissue edema surrounding affected bones

Critical advantage: Whole-body MRI identifies subclinical lesions not apparent on clinical examination, which is essential since 89% of patients have multifocal involvement 5.

Anatomical Distribution Patterns

Most Common Sites (in descending order) 5, 3:

1. Tibia - 68% of patients, 29% of all lesions
2. Clavicle - 38% of patients
3. Spine - 19-25% of patients
4. Feet - 25% of lesions
5. Femur - 12.5% of lesions
6. Ribs - 16.7% of lesions
7. Pelvis, mandible, sternum (less common)

Two Distinct Phenotypic Patterns 5:

Pattern 1: "Tibio-appendicular multi-focal pattern" (54% of cases)

• Tibial involvement present
• NO clavicular involvement
• Multiple additional lesions
• Mean 8.6 lesions per patient

Pattern 2: "Claviculo-spinal pauci-focal pattern" (24% of cases)

• Clavicular lesions present
• NO tibial involvement
• Few additional lesions, mainly spine
• Fewer total lesions

Only 14% have synchronous clavicle AND tibia involvement - this is an important diagnostic clue 5.

Bilateral and Symmetric Disease

Bilateral involvement is characteristic 5:

• Fibulas: 80% bilateral
• Tibias: 68% bilateral
• Foot phalanges: 67% bilateral
• 93% of bilateral disease shows symmetry
• 66% of symmetric tibial lesions are of equal severity bilaterally

This bilateral symmetric pattern is highly suggestive of CRMO and helps differentiate it from infectious osteomyelitis or malignancy.

Nuclear Medicine Findings

Bone Scintigraphy 6:

• Useful for detecting multifocal involvement and extent of disease
• Shows increased uptake at affected sites
• Particularly valuable for identifying clinically silent lesions
• Can detect disease when radiographs are normal

Alternative nuclear imaging 4: [99mTc]Tc-HDP SPECT/CT or PET/CT with bone-seeking radiotracers are reasonable alternatives when MRI is contraindicated.

Vertebral Involvement

Vertebral lesions require special attention 1:

• Often multifocal in spine
• Can lead to vertebral collapse requiring long-term monitoring
• Sagittal spinal imaging is essential on whole-body MRI 4
• 19-25% of patients have spinal involvement 5, 3

Diagnostic Imaging Algorithm

Step 1: Plain radiographs of symptomatic area (initial screening)

Step 2: Whole-body MRI with sagittal spinal images (preferred) 4 to:

• Map all active lesions (including subclinical)
• Assess disease extent
• Identify characteristic distribution patterns
• Evaluate for bilateral symmetric involvement

Alternative to Step 2: If MRI contraindicated, use [99mTc]Tc-HDP SPECT/CT, PET/CT with bone-seeking radiotracer, or bone scintigraphy 4

Step 3: Targeted MRI of specific regions for detailed evaluation of individual lesions

Critical Diagnostic Pitfalls

1. Do NOT rely solely on radiographs - they miss early disease and underestimate extent 3

2. Unifocal presentation occurs in 11% 5 - absence of multifocal disease does not exclude CRMO; whole-body imaging may reveal additional subclinical lesions

3. Mimics malignancy radiologically 7 - the combination of destructive bone lesion, periosteal reaction, and soft tissue involvement can appear identical to Ewing's sarcoma or osteosarcoma

4. Avoid routine bone biopsies 4 - reserve for cases with inconclusive imaging or suspicion of malignancy/infectious osteomyelitis

5. CT generally avoided due to radiation exposure in pediatric population 3, though it can show periosteal reaction, trabecular coarsening, and cortical erosions 8

The recognition of these characteristic imaging patterns—particularly the bilateral symmetric metaphyseal involvement of long bones, the two distinct phenotypic patterns, and the multifocal nature revealed by whole-body MRI—allows confident diagnosis in the appropriate clinical setting without unnecessary biopsies or prolonged antibiotic treatment 2.