What is the next step for a patient with a lytic lesion in the inferior right occipital bone and normal labs?

Next Step: Obtain Whole-Body Low-Dose CT and Complete Myeloma Laboratory Workup

The immediate next step is to obtain whole-body low-dose CT (WBLD-CT) to determine if this is a solitary lesion or part of systemic disease, combined with a complete myeloma laboratory workup including serum protein electrophoresis with immunofixation, serum free light chain assay, and quantitative immunoglobulins. 1, 2

Rationale for Whole-Body Imaging

• WBLD-CT is the grade 1A recommendation for evaluating lytic bone lesions, as it detects 60% more relevant findings than conventional X-rays and provides superior evaluation of cortical bone detail and areas at risk of fracture 1
• Whole-body imaging is mandatory to distinguish between a solitary bone lesion (which has dramatically different management) versus systemic disease such as multiple myeloma 1, 2
• The patient already has adequate local characterization with both CT and MRI of the skull, so the critical missing piece is systemic evaluation 1

Essential Laboratory Workup

Order the following tests immediately to exclude multiple myeloma/plasma cell dyscrasia:

• 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
• Complete blood count (already done—normal) 1
• Serum calcium (already done—normal at 9.0 mg/dL) 1
• Creatinine and albumin (already done—normal) 1
• 24-hour urine for total protein with urine protein electrophoresis (UPEP) and urine immunofixation electrophoresis (UIFE) 1

Why Multiple Myeloma/Solitary Plasmacytoma is the Primary Concern

• Lytic lesions are present in approximately 80-90% of multiple myeloma patients at diagnosis 3, 4
• Multiple myeloma presents as mixed lytic-sclerotic lesions in two-thirds of cases, with preferential replacement of trabecular bone while cortical bone remains partly conserved—exactly matching this patient's imaging showing cortical thinning with an expansile lytic lesion 1, 2
• The skull is a preferential site for myelomatous involvement 4
• Normal CBC does not exclude myeloma, as many patients present with isolated bone disease 1

Bone Marrow Evaluation Timing

• Perform bone marrow aspiration and biopsy with flow cytometry if:

  • WBLD-CT shows additional lesions (confirming systemic disease) 1
  • Laboratory workup reveals monoclonal protein or abnormal free light chain ratio 1
  • WBLD-CT shows only this solitary lesion AND labs are abnormal (to diagnose solitary plasmacytoma) 1, 2

• Flow cytometry is critical because it 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%) 1, 2

• Bone marrow plasmacytosis >10% excludes solitary plasmacytoma and confirms multiple myeloma 1, 2

Alternative Diagnoses to Consider

While multiple myeloma is the primary concern given the imaging characteristics, other possibilities include:

• Metastatic disease: WBLD-CT will identify primary tumor sites if present 1
• Langerhans Cell Histiocytosis: More common in younger patients, but possible 1
• Primary bone tumors (Ewing's sarcoma, hemangioendothelioma): Rare in the occipital bone but reported 5, 6

Critical Pitfalls to Avoid

• Do not proceed directly to biopsy without systemic imaging—if this is multiple myeloma with multiple lesions, the diagnosis and management are entirely different than a solitary lesion 1, 2
• Do not rely on normal CBC and calcium to exclude myeloma—many patients with early or solitary disease have normal routine labs 1
• Do not skip the specialized myeloma labs (SPEP, SIFE, FLC)—these are far more sensitive than routine labs for detecting plasma cell disorders 1, 2
• Do not miss soft tissue extension—the MRI already shows minimal dural thickening near the hypoglossal canal, which requires careful monitoring 1

Summary Algorithm

1. Order WBLD-CT of entire skeleton (grade 1A recommendation) 1
2. Order complete myeloma laboratory panel (SPEP/SIFE, FLC, quantitative Ig, UPEP/UIFE) 1, 2
3. If WBLD-CT shows multiple lesions OR labs are abnormal: Proceed to bone marrow biopsy with flow cytometry 1, 2
4. If WBLD-CT shows only solitary lesion AND labs are normal: Consider PET/CT for further characterization and discuss at multidisciplinary tumor board for biopsy planning 1