What is the next step in evaluating a patient with a lytic lesion in the right paramedian inferior occipital skull, suspected to be multiple myeloma, metastatic disease, or lymphoproliferative disorder, with stable lesion size and minimal dural thickening on MRI?

Next Step in Evaluation: PET/CT is Recommended

The next step in evaluating this patient with a lytic skull lesion is to obtain PET/CT imaging, as explicitly recommended in the radiology report and strongly supported by current guidelines for suspected multiple myeloma and plasma cell disorders. 1, 2

Rationale for PET/CT as the Next Step

Primary Diagnostic Objectives

PET/CT serves two critical functions in this clinical scenario:

• Systemic disease detection: PET/CT is essential to determine whether this represents a solitary plasmacytoma versus disseminated multiple myeloma, which fundamentally changes prognosis and treatment. 1, 2

• Staging accuracy: In patients with suspected active multiple myeloma with lytic lesions at CT (as in this case), PET/CT should be performed for staging with a grade 1A recommendation. 1

• Sensitivity for focal lesions: PET/CT demonstrates 90% sensitivity for detecting focal myelomatous lesions greater than 5 mm and is superior to conventional radiography in detecting lytic disease. 1, 3, 4

Guideline-Based Recommendations

The 2023 European Association of Nuclear Medicine consensus specifically states that patients with suspected active multiple myeloma with lytic lesions at LDCT should undergo staging using PET/CT (median consensus score 9.0/9.0). 1

Whole-body low-dose CT (WBLD-CT) is the novel standard procedure for diagnosis of lytic disease in multiple myeloma (grade 1A), detecting up to 60% more relevant findings than conventional radiography. 1, 3, 2

Concurrent Essential Workup

Laboratory Evaluation Required Immediately

A complete plasma cell dyscrasia panel must be ordered concurrently:

• Serum protein electrophoresis (SPEP) with immunofixation electrophoresis (SIFE) 1, 2
• Serum free light chain (FLC) assay 1, 2
• Quantitative immunoglobulin levels (IgG, IgA, IgM) 1
• 24-hour urine for total protein with urine protein electrophoresis (UPEP) and urine immunofixation electrophoresis (UIFE) 1, 2
• Complete blood count with differential 1
• Serum creatinine and calcium levels 1

Bone Marrow Evaluation Timing

Bone marrow aspiration and biopsy with flow cytometry should be performed if:

• PET/CT or laboratory findings suggest plasma cell dyscrasia 1, 2
• This is mandatory for diagnosing solitary plasmacytoma versus multiple myeloma 1, 2

Critical diagnostic consideration: Flow cytometry can detect occult bone marrow disease in 49-68% of patients with apparent solitary plasmacytoma, and these patients have significantly higher progression rates to multiple myeloma (71-72% versus 8-12.5%). 2

Critical Pitfalls to Avoid

Biopsy Timing

Never perform internal fixation of a pathological fracture before obtaining a biopsy - this is a critical error that can compromise diagnosis and treatment. 2

Imaging Limitations

• Conventional X-rays should not be relied upon solely, as lytic lesions only become visible after more than 50% of trabecular bone has been lost. 3, 2, 4
• While this patient already has MRI showing the lesion characteristics, MRI depicts bone marrow involvement while CT and PET/CT reveal lytic lesions and metabolic activity. 1, 3

Differential Diagnosis Considerations

The imaging characteristics described (hyperintense T1 and T2 signal with moderate enhancement, no restricted diffusion, minimal dural thickening) are consistent with:

• Multiple myeloma (most common cause of lytic skull lesions in adults) 2
• Solitary plasmacytoma (requires exclusion of systemic disease) 1, 2
• Metastatic disease (PET/CT helps identify primary tumor) 5
• Lymphoproliferative disorder including Langerhans cell histiocytosis (less likely given imaging characteristics) 6

Algorithmic Approach Summary

1. Order PET/CT immediately (as recommended in radiology report) 1, 2
2. Obtain complete plasma cell dyscrasia laboratory panel concurrently 1, 2
3. Perform bone marrow aspiration and biopsy with flow cytometry if imaging or labs suggest plasma cell disorder 1, 2
4. Obtain tissue biopsy of the lesion if diagnosis remains uncertain after above workup, ensuring adequate tissue for histology and molecular testing 2

The presence of more than 1 focal lesion on whole-body imaging would characterize this as symptomatic disease requiring therapy, even without additional visible lytic lesions. 1, 3