Multiple myeloma is a cancer formed by malignant plasma cells. As these cancerous cells accumulate in the bone marrow, they disrupt normal bone production and can lead to significant skeletal damage. This makes imaging an important part of diagnosing the condition, tracking its progression, and guiding treatment. Understanding the extent of bone involvement is necessary for properly staging the disease and assessing prognosis.
The Role of CT Scans in Diagnosing Multiple Myeloma
For many years, the standard for assessing bone damage in multiple myeloma was a skeletal survey using X-rays. However, X-rays have limitations in their sensitivity, as they can only detect bone damage after a significant amount of bone mineral has been lost. This means smaller or earlier lesions could be missed.
Modern diagnostic guidelines now recommend a low-dose whole-body CT (LDWBCT) scan as the preferred method for the initial evaluation of bone disease. A CT scan uses X-rays and computing to create detailed, cross-sectional images of the body. Its enhanced sensitivity allows it to identify areas of bone destruction much earlier and more accurately than a traditional X-ray.
A whole-body protocol provides a comprehensive survey of the entire skeleton in a single, quick procedure. This complete view is important for accurately staging the disease, as the number and location of bone lesions are factored into risk assessment. By identifying all affected areas, clinicians can better predict the risk of fractures and determine the appropriate therapy.
Interpreting CT Scan Results
The most characteristic finding on a CT scan for multiple myeloma is the presence of lytic lesions. These are areas where the bone has been eroded, creating what are often described as “punched-out” holes. These lesions are a direct result of the myeloma cells disrupting the normal balance of bone breakdown and formation.
Beyond distinct lesions, the scan may reveal more widespread bone thinning, a condition known as osteopenia. This generalized weakening of the skeleton can increase the risk of fractures even without a focal lesion. A CT scan is very effective at detecting these subtle changes in bone density.
A CT scan can also identify a pathologic fracture, which is a break in a bone weakened by the disease, often from minimal or no trauma. The scan can identify not only overt fractures but also small stress fractures or areas of cortical bone erosion that indicate a high risk of a future break. Finally, the scan can visualize soft tissue masses called plasmacytomas, which are collections of myeloma cells that can form adjacent to the bone.
The CT Scan Procedure
Preparation for a low-dose whole-body CT scan is minimal. You will be asked to wear comfortable clothing without metal zippers or buttons and to remove any jewelry, glasses, or metal objects that could interfere with the imaging.
In some cases, a contrast agent may be administered through an intravenous (IV) line. This dye helps to highlight blood vessels and organs, providing a clearer picture of soft tissues. While not always necessary for evaluating bone destruction, it can be useful for identifying plasmacytomas or assessing organ involvement.
During the scan, you will lie on a motorized table that moves through the center of a large, ring-shaped machine. The scanner is open, which helps alleviate feelings of claustrophobia. The procedure is painless, and you will need to remain still while the images are captured, which takes only a few minutes.
Comparison to Other Imaging Techniques
Other imaging modalities provide complementary information. Magnetic resonance imaging (MRI) is particularly effective at visualizing soft tissues. It is the most sensitive method for directly viewing the bone marrow to detect infiltration by myeloma cells, even before bone damage occurs. An MRI is often used to evaluate the spine for nerve or spinal cord compression.
A PET/CT scan combines the anatomical detail of a CT with a functional assessment of metabolic activity. Before the scan, the patient receives an injection of a radioactive tracer that is absorbed by cells with high energy use, such as cancer cells. This allows the PET scan to light up active disease sites, making it valuable for assessing response to treatment.
The conventional X-ray has been largely superseded due to its lower sensitivity. It often cannot detect bone lesions until 30-50% of the bone mineral in a specific area has been lost. While it may still be used in certain situations, LDWBCT, MRI, and PET/CT each offer a more detailed view of the disease to guide patient care.