Why is a PET Scan Necessary in Myeloma?

PET scans, otherwise known as Positron Emission Tomography scans, can be a helpful tool when diagnosing or monitoring multiple myeloma. Many myeloma patients will experience what it's like to receive a PET scan and discuss the results with their healthcare teams. 

What is a PET Scan Used For? Why Would a Doctor Order a PET Scan? 

A PET scan can provide useful information, especially about the presence of active myeloma lesions and areas of bone involvement. PET scans use a radioactive tracer that accumulates in areas of increased metabolic activity, which can be indicative of cancerous growth. This can help in identifying active lesions in bones and other tissues, which is important for assessing the extent of the myeloma and planning treatment strategies.

PET scans can be particularly useful in cases where there is uncertainty about the disease's extent or when the disease is suspected to be more advanced than initially thought. However, it's important to note that while PET scans can provide valuable information, they are usually used in conjunction with other diagnostic tools, such as the CT scan and the MRI, for a comprehensive assessment of your multiple myeloma stage and progression.

John Hopkins Medicine shares,

"PET scans are most often used by oncologists, neurologists, and neurosurgeons (doctors specializing in the treatment and surgery of the brain and nervous system), and cardiologists (heart doctors). However, as advances in PET technologies continue, this procedure is beginning to be used more widely in other areas."

Why Do I Need a PET Scan For Multiple Myeloma?

A PET scan is used in the context of multiple myeloma for several important reasons:

1. Assessment of Active Disease: PET scans can detect areas of increased metabolic activity in the body. In multiple myeloma, these areas correspond to active myeloma lesions in bones and other tissues. Identifying these active lesions is crucial for determining the extent of the disease and planning appropriate treatment strategies.
2. Staging and Treatment Planning: While PET scans are not the primary method for staging multiple myeloma, they can provide additional information to complement other staging methods. By identifying active lesions and areas of bone involvement, PET scans contribute to a more accurate assessment of the disease's stage. This information is essential for determining the appropriate treatment approach and prognosis.
3. Monitoring Response to Treatment: After initiating treatment for multiple myeloma, regular PET scans can be used to monitor how well the treatment is working. A decrease in metabolic activity in previously active lesions on a PET scan indicates a positive response to treatment. This helps doctors gauge the effectiveness of the chosen therapy and make any necessary adjustments to the treatment plan.
4. Detection of Relapse: PET scans can also be used to detect disease relapse or progression. If there is a recurrence of active lesions or new areas of increased metabolic activity, it could indicate that the disease has become more aggressive or resistant to previous treatments. Early detection of relapse allows for prompt intervention and modification of the treatment approach.
5. Localization for Biopsy: In some cases, a PET scan can help guide the selection of biopsy sites. If there are suspicious areas of increased metabolic activity, a biopsy can be performed to confirm the presence of myeloma cells and determine their characteristics.

How Does Multiple Myeloma Show Up On a PET Scan?

The PET Scan allows radiologists and multiple myeloma specialists to see inside the bone marrow, where the actual disease takes place. It's also a useful tool for seeing focal lesions, especially after therapy. If there's an uptake on the nuclear tracer, it still means there is disease activity that might not be seen on an MRI (magnetic resonance imaging). 

What is the Difference Between a CT and a PET Scan?

Commonly, PET and CT (Computed Tomography) scans are performed at the same time.

A CT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body.  CT scans can help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage.

If residual lesions are still present on the PET-CT after therapy, this is a high concern, as it is likely that the focal lesions might indicate a relapse of the disease.

To note, the results of a CT can be negative, but an MRI can still be positive, so both tests (along with the PET scan) are needed for myeloma patients, especially for newly diagnosed and smoldering patients. It's better to be safe than sorry and have the whole picture available to yourself and your treating team. 

Does a PET Scan Tell You The Stage of Myeloma?

A PET scan can provide valuable information about the stage and extent of multiple myeloma. However, a PET scan is typically not used as the primary method for staging multiple myeloma. Instead, it is often used in combination with other imaging techniques and tests to gather a comprehensive understanding of the disease's progression.

Staging in multiple myeloma is commonly done using the International Staging System (ISS) or the Revised International Staging System (R-ISS), both of which take into account factors like serum levels of specific proteins (beta-2 microglobulin and albumin) and chromosomal abnormalities detected through cytogenetic tests.

How Accurate is A PET Scan for Multiple Myeloma?

Like any medical test, the accuracy of a PET scan can vary depending on several factors:

1. Sensitivity and Specificity: Sensitivity refers to the ability of a test to correctly identify true positive cases (i.e., accurately detect the presence of the condition). Specificity refers to the ability of a test to correctly identify true negative cases (i.e., accurately rule out the absence of the condition). The sensitivity and specificity of a PET scan for multiple myeloma can vary, but it generally has a higher sensitivity than traditional imaging methods like X-rays or CT scans, especially for detecting small or subtle lesions.

2. Disease Characteristics: The accuracy of a PET scan may be influenced by the characteristics of the myeloma lesions. Highly active and metabolically active lesions are more likely to be detected on a PET scan. Lesions with lower metabolic activity or those that are not causing significant disruption to the bone structure might be more challenging to detect.

3. Background Activity: PET scans rely on the detection of increased metabolic activity in tissues. Sometimes, non-cancerous conditions or infections can also cause increased metabolic activity, leading to false-positive results. Therefore, it's important for the interpreting physician to consider the context and other clinical information.

4. Combination with Other Imaging: In clinical practice, PET scans are often used in conjunction with other imaging modalities, such as CT scans or MRI scans. Combining multiple imaging techniques can enhance the accuracy of detecting and characterizing lesions.

5. Expert Interpretation: The accuracy of PET scan results can also be influenced by the expertise of the physician interpreting the scan. Experienced professionals, such as radiologists familiar with multiple myeloma and multiple myeloma specialists, are more likely to identify and interpret lesions accurately.

6. Disease Stage: The accuracy of a PET scan might vary based on the stage of the disease. In the very early stages of multiple myeloma, there might be fewer lesions or lower metabolic activity, which could impact the scan's sensitivity.

What Imaging is Needed for Multiple Myeloma?

As stated throughout the article, the typical imaging tests used to diagnose and monitor multiple myeloma are PET scans, CT scans, and MRIs. X-rays can be used, but because they are not as sensitive as the other aforementioned tests, they are rarely used in today's myeloma.

What Conditions Are Mistaken for Myeloma?

Many myeloma patients experience delayed diagnoses due to the fact that multiple myeloma is so similar to many other diseases out there (and some of the symptoms of myeloma could be attributed to growing older- back pain, fatigue, etc.) However, it is also possible that someone mistakenly receives a diagnosis of multiple myeloma while actually having a similar but different diagnosis. 

Here are some conditions that could be mistaken for myeloma: 

• Monoclonal Gammopathy of Undetermined Significance (MGUS) 
• Amyloidosis 
• Waldenström Macroglobulinemia 
• Lymphoma 
• Metastatic cancer 
• Chronic infections 
• Osteoporosis or Osteopenia 
• Other rare hematologic conditions 

A proper diagnosis requires a combination of clinical evaluation, laboratory tests (including blood and urine tests), imaging studies (such as X-rays, CT scans, and MRI scans), and sometimes bone marrow biopsies. A multidisciplinary approach involving hematologists, oncologists, radiologists, and other specialists is often necessary to accurately distinguish multiple myeloma from other conditions and provide appropriate treatment and management.

Imaging in Myeloma Resources 

To learn more about imaging in myeloma, watch the following course in HealthTree University: Unit 14 Imaging in Myeloma

Dr. Jens Hillengass shares his thoughts on imaging in myeloma through this podcast: What You Need to Know About Right Myeloma Imaging 

Looking for a multiple myeloma specialist? Find one here: Myeloma Specialist Directory