What does a decrease in signal intensity of the myelomatous lesion and a decrease in the number of lesions, with no abnormal leptomeningeal enhancement, indicate in terms of treatment response for a patient with multiple myeloma?

Treatment Response Assessment in Multiple Myeloma

A decrease in signal intensity and number of myelomatous lesions on imaging, with no abnormal leptomeningeal enhancement, indicates a favorable treatment response and should prompt continued monitoring with the current therapeutic regimen.

Imaging-Based Response Assessment

Modern imaging modalities are essential for evaluating treatment response in multiple myeloma, with MRI and PET/CT providing superior sensitivity compared to conventional methods. 1

Standard Imaging Approach

• Whole-body low-dose CT (WBCT) is the preferred method for routine bone surveillance and monitoring treatment response, as it detects up to 60% more relevant findings than skeletal surveys and leads to treatment changes in up to 20% of patients 1

• MRI and FDG-PET/CT serve as valuable alternatives for baseline assessment and response monitoring, particularly in nonsecretory or oligosecretory myeloma where traditional markers are unreliable 1

• Response assessment should occur with each treatment cycle during active therapy, with frequency reduced to every 3 months once best response is achieved or during maintenance therapy 1

Interpreting Decreased Lesion Burden

The findings you describe—decreased signal intensity and reduced number of lesions—represent objective radiographic improvement that correlates with treatment efficacy.

What This Means Clinically

• Decreased signal intensity on MRI indicates reduced metabolic activity and tumor burden within previously identified myelomatous lesions 2

• A reduction in the number of visible lesions suggests effective cytoreduction and disease control with current therapy 1

• These imaging improvements should be correlated with biochemical markers (serum/urine M-protein and free light chains) to comprehensively assess depth of response 1

Significance of Absent Leptomeningeal Enhancement

The absence of abnormal leptomeningeal enhancement is particularly reassuring, as leptomeningeal myelomatosis represents a rare but devastating complication with extremely poor prognosis.

Clinical Context

• Leptomeningeal involvement occurs in less than 1% of multiple myeloma patients but carries a median survival of only 2 months from diagnosis 3, 4

• Contrast-enhanced brain MRI showing no leptomeningeal enhancement effectively excludes central nervous system involvement, which would manifest as nodular enhancement of the pia mater extending into subarachnoid spaces 3

• This finding is critical because leptomeningeal disease has a 6-month neurologic progression-free survival rate of only 7% and responds poorly to treatment 4

Clinical Action Plan

Based on these favorable imaging findings, the recommended approach is:

Immediate Management

• Continue current anti-myeloma therapy without modification, as the imaging demonstrates objective response 1, 5

• Obtain concurrent biochemical assessment (serum/urine electrophoresis, free light chains) to confirm concordance between radiographic and laboratory response 1

• Document the depth of response using International Myeloma Working Group criteria, which requires correlation of imaging with bone marrow assessment for complete response determination 5, 6

Ongoing Monitoring

• Repeat imaging at 3-month intervals once plateau response is achieved to monitor for disease progression 1

• Maintain vigilance for new neurologic symptoms that could indicate late leptomeningeal involvement, though current imaging excludes this complication 3

• Consider less frequent imaging (every 3-6 months) if patient achieves very good partial response or better and remains on maintenance therapy 1

Common Pitfalls to Avoid

Several important caveats warrant attention when interpreting these findings:

• Do not rely solely on imaging for response assessment—biochemical markers remain the standard for quantifying treatment response and must show concordant improvement 1

• Skull and rib lesions may not be well detected by WBCT or MRI compared to focused X-rays, so consider supplemental imaging if these areas are clinically concerning 1

• MRI can occasionally show nonspecific lesions and may overestimate disease extent, so correlation with clinical and laboratory findings is essential 1

• In patients with oligosecretory or nonsecretory myeloma, imaging becomes even more critical as biochemical markers are unreliable for monitoring 1