Are lytic lesions the same as myelomatous lesions?

Are Lytic Lesions the Same as Myelomatous Lesions?

No, lytic lesions and myelomatous lesions are not the same—lytic lesions refer specifically to areas of bone destruction visible on imaging, while myelomatous lesions encompass a broader spectrum of disease manifestations including both bone marrow infiltration and osteolytic bone destruction.

Key Distinctions

Lytic Lesions

• Lytic lesions are areas of bone destruction that appear as "punched-out" osteolytic defects on imaging, characterized by well-defined, round radiolucent areas without sclerotic borders, often described as having a "raindrop" or "Swiss cheese" appearance 1
• These lesions only become visible on conventional X-ray after more than 50% of trabecular bone has been lost 2, 1
• Lytic lesions are present in approximately 80-90% of multiple myeloma patients at diagnosis and result from increased osteoclastic activity with suppressed osteoblastic function 2

Myelomatous Lesions (Broader Category)

• Myelomatous lesions include both bone marrow infiltration by plasma cells AND resulting bone destruction 2
• MRI depicts bone marrow involvement (focal lesions representing localized plasma cell infiltration), while CT and skeletal surveys reveal lytic lesions (actual bone destruction) 2
• Not all focal lesions seen on MRI showing bone marrow infiltration will have corresponding osteolytic destruction—in one study, only 59.3% of focal lesions in the axial skeleton on MRI had corresponding bone destruction on CT 3

Clinical Implications

Why This Distinction Matters

• A patient can have myelomatous bone marrow involvement without lytic bone destruction 2
• In asymptomatic patients with no lytic disease on WBLD-CT, whole-body MRI must be performed, and the presence of more than 1 focal lesion characterizes the patient as having symptomatic disease requiring therapy, even without visible lytic lesions 2
• This explains why imaging algorithms now incorporate both modalities: WBLD-CT for detecting lytic bone destruction and MRI for detecting earlier bone marrow infiltration 2

Imaging Algorithm

• WBLD-CT is the standard procedure for diagnosing lytic disease (grade 1A recommendation), detecting up to 60% more relevant findings than conventional radiography 2, 4
• MRI is essential for detecting bone marrow involvement before lytic destruction occurs, particularly in asymptomatic patients 2, 5
• PET/CT is useful for defining complete response and disease progression, with 90% sensitivity for detecting focal lesions greater than 5 mm 1, 4

Common Pitfalls

Terminology Confusion

• Clinicians sometimes use "myelomatous lesions" and "lytic lesions" interchangeably, but this is imprecise 2
• Lytic bone disease can be diffuse and may be confused with benign osteoporosis—the presence of discrete lytic lesions is characteristic of myeloma, while ordinary osteoporosis shows diffuse bone loss without focal destructive lesions 2, 5

Diagnostic Considerations

• Other plasma cell dyscrasias (such as Waldenstrom's macroglobulinemia) can rarely present with lytic lesions, though this is uncommon 6
• Bone metastases from solid tumors can coexist with multiple myeloma in the same patient, making differentiation challenging 7
• Neither morphological characteristics nor texture features can reliably predict which focal lesions on MRI will develop corresponding bone destruction on CT 3