When Punched-Out Lesions Are Seen in Multiple Myeloma
Punched-out lytic lesions are characteristic findings in active (symptomatic) multiple myeloma and appear on imaging when patients meet diagnostic criteria for bone disease requiring treatment. These lesions represent areas of osteolytic bone destruction caused by uncoupling of bone remodeling, with increased osteoclast activity and suppressed osteoblast function 1.
Timing and Clinical Context
Punched-out lesions are typically detected at initial diagnosis in symptomatic multiple myeloma patients who meet CRAB criteria (hypercalcemia, renal insufficiency, anemia, and bone lesions) 2. Approximately 79% of patients with multiple myeloma have osteolytic bone disease at presentation 3.
Key Diagnostic Scenarios:
Active/Symptomatic Disease: The presence of one or more osteolytic lesions on skeletal radiography, whole-body CT, or PET-CT fulfills the bone disease criterion for active myeloma requiring treatment 2
Skull Involvement: The skull is a preferential site, showing numerous well-circumscribed, punched-out lytic lesions without reactive bone formation, often described as having a "raindrop" or "Swiss cheese" appearance 4, 1
Detection Threshold: Lytic lesions only become visible on conventional X-ray after more than 50% of trabecular bone has been lost 4
Imaging Modality Considerations
Whole-body low-dose CT (WBLD-CT) is now the recommended standard for detecting lytic bone disease, as it detects up to 60% more relevant findings compared to conventional skeletal surveys 5, 4. However, the classic punched-out appearance is most characteristically described on skull X-rays 4, 1.
Imaging Algorithm:
- First-line: WBLD-CT can detect lesions with less than 5% trabecular bone destruction 1
- Skull-specific: Conventional X-rays remain valuable for skull and rib lesions, which are not as well detected by WBLD-CT or MRI 5, 4
- FDG PET/CT: Has 90% sensitivity for detecting focal lesions >5mm and helps differentiate active from inactive disease 2, 5
Important Clinical Pitfalls
Punched-out lesions persist after treatment, making it difficult to distinguish old inactive lesions from new active ones on conventional imaging 6. This is why:
- Functional imaging (PET/CT) is superior for assessing treatment response and detecting active disease in relapsed settings 6, 7
- Serial imaging every 3 months during active treatment is recommended to monitor for new bone lesions 5
- MRI cannot always differentiate treated bone marrow lesions from viable neoplastic tumors 5
The characteristic appearance is well-defined, round radiolucent defects WITHOUT sclerotic borders or reactive bone formation 4, 1. This distinguishes myeloma from other conditions that typically show reactive bone changes.