Contrast-enhanced ultrasound-guided biopsy and perfusion monitoring for bladder involvement in relapsed multiple myeloma: a case report.

OBJECTIVE: Extramedullary involvement of the urinary bladder by plasma cell myeloma is extremely rare. This report presents a case to explore the clinical application value of contrast-enhanced ultrasound (CEUS) in the diagnosis and therapeutic monitoring of this condition. METHODS: A 54-year-old man with high-risk multiple myeloma (IgAλ type, R-ISS stage II, 1q21 amplification) developed newly-onset urinary frequency during systemic therapy. Grayscale ultrasound, color Doppler ultrasound, and CEUS were performed, followed by CEUS-guided percutaneous biopsy. After pathological confirmation, salvage therapy was administered, and follow-up CEUS was performed to evaluate treatment response. RESULTS: Grayscale ultrasound showed diffuse thickening of the bladder wall (maximum thickness approximately 2.5 cm) with abundant color Doppler flow signals. CEUS observed a perfusion pattern of "rapid arterial uptake, slow washout, and hyperenhancement": the muscular layer demonstrated early enhancement at 11 seconds with centrifugal (serosal-to-mucosal) filling, and marked contrast agent retention was observed during the venous phase. CEUS-guided biopsy and subsequent immunohistochemistry confirmed monoclonal plasma cell myeloma infiltration of the bladder (strongly positive for CD38, kappa-negative, lambda-positive). Follow-up CEUS after salvage therapy demonstrated a reduction in bladder wall thickness to 0.72 cm with delayed arterial enhancement. CONCLUSION: CEUS-guided transabdominal biopsy targeting the muscular layer may be considered in patients with suspected bladder plasmacytoma and high-risk features for transurethral resection to avoid false negatives from mucosal sampling. Furthermore, CEUS provides a nephrotoxicity-free modality for monitoring treatment response.