Lenalidomide is the Most Likely Culprit
Lenalidomide (option b) is the drug most likely responsible for unilateral leg swelling in this multiple myeloma patient, as it carries a well-established risk of venous thromboembolism (VTE), which commonly presents as unilateral leg swelling from deep venous thrombosis (DVT).
Rationale Based on Thrombotic Risk
Lenalidomide and VTE Risk
- Lenalidomide, particularly when combined with dexamethasone, significantly increases the risk of venous thromboembolism 1, 2.
- The incidence of DVT is low with single-agent lenalidomide or lenalidomide plus low-dose dexamethasone, but risk rises substantially when combined with high-dose dexamethasone 1.
- All immunomodulatory drugs (IMiDs), including lenalidomide, share the potential adverse effect of thrombosis, and prophylactic anticoagulation is recommended unless contraindicated 2.
- Unilateral leg swelling is a classic presentation of DVT, which is the most common manifestation of VTE in patients receiving lenalidomide-based therapy 1.
Comparison with Other Agents
Bortezomib:
- The primary toxicities of bortezomib are peripheral neuropathy (not leg swelling), thrombocytopenia, neutropenia, and gastrointestinal adverse events 2, 3.
- Bortezomib does not carry a significant thrombotic risk 2, 1.
Melphalan:
- Melphalan's main toxicities are hematologic (bone marrow suppression), gastrointestinal toxicity, and pulmonary toxicity 4.
- There is no established association between melphalan and venous thromboembolism 4.
Cyclophosphamide:
- Cyclophosphamide is associated with myelosuppression, hemorrhagic cystitis, and gastrointestinal effects 5.
- It does not have a notable thrombotic risk profile 3, 1.
Clinical Management Implications
Immediate Evaluation Required
- Unilateral leg swelling in a patient on lenalidomide and dexamethasone should prompt immediate evaluation for DVT with Doppler ultrasound 1.
- This is a potentially life-threatening complication that can lead to pulmonary embolism if untreated 2.
Thromboprophylaxis Considerations
- NCCN guidelines specifically recommend appropriate thromboprophylaxis for patients receiving lenalidomide-based therapy 1.
- Aspirin may be adequate for average-risk patients, but low-molecular-weight heparin or oral vitamin K antagonists may be needed for higher-risk patients 2.
- The combination of lenalidomide with dexamethasone (especially high-dose) places patients at higher risk, necessitating more aggressive thromboprophylaxis 1.
Common Pitfall to Avoid
A critical error would be attributing the leg swelling to peripheral neuropathy from bortezomib, as neuropathy presents with sensory changes, pain, and weakness—not unilateral swelling 2, 3. The unilateral nature of the swelling strongly suggests a vascular etiology (DVT) rather than a neurologic or systemic process 1.