Magnetic resonance imaging (MRI) is a powerful imaging technique for visualizing the muscles, organs, brain, and spinal cord — but is it useful for detecting spinal muscular atrophy (SMA)?
While the gold standard SMA diagnostic tool is genetic testing, your doctor or neurologist (a brain and spinal cord specialist) may order an MRI scan to help with diagnosis or SMA treatment plans. This article will break down what MRI is, how it works, and when it may be used with SMA.
MRI is an imaging technique that uses extremely powerful magnets to create detailed 3D images of your body’s tissues. The magnets create a strong magnetic field that interacts with the atoms in your body. The MRI machine reads these interactions and produces pictures that your doctor reviews and analyzes.
During the scan, you’ll lie completely still on a scan table. The table will move into the MRI machine, which is shaped like a giant tube. The machine can be very loud inside the tube, so you’ll be given headphones to block the noise or listen to music.
In some cases, your doctor may use a contrast agent, like gadolinium, given intravenously (through an IV) as part of the MRI scan. This special dye can make MRI images brighter, helping your doctor better see your tissues.
MRI scans are a great tool for looking at your muscles, brain, and spinal cord, while other imaging techniques like X-rays and CT scans are better for visualizing your bones. Unlike X-rays, the MRI machine doesn’t produce any radiation.
However, the magnetic field it makes is strong enough to pull any metal object in the room to it — including metal implants and even wheelchairs. Be sure to let your doctor know if you have any metal in your body before an MRI. If this metal is not safe for an MRI machine, your doctor will use a different imaging technique.
MRI is an extremely useful tool for diagnosing several health conditions, but is it useful for people with SMA? Doctors and researchers are finding MRI may be helpful along with other tests used to diagnose SMA, as it can rule out other conditions. MRI scans can also help with tracking SMA treatment progress.
SMA is a neuromuscular disease that causes nerve degeneration and muscle weakness. Specifically, it affects the motor neurons or nerve cells in the spinal cord. While an MRI scan isn’t always part of diagnosing SMA, doctors and researchers have performed imaging studies to figure out what happens in the body with this disease.
They’ve found that SMA causes degeneration in the anterior horn of the spinal cord. This area contains motor neurons and is responsible for sending electrical signals out to the skeletal muscles. Without signals from the spinal cord, the muscles can’t move and begin wasting away — known as muscle atrophy.
In the past, spinal cord degeneration was usually only discovered during an autopsy examination. More recently, however, doctors and researchers have suggested that MRI scans may be useful for visualizing and diagnosing SMA.
Most SMA cases are caused by changes or mutations in the survival motor neuron 1 (SMN1) gene. Specifically, this is a deletion or missing portion of chromosome 5. This gene provides instructions for making the SMN protein. Motor neurons need this protein to function properly — without it, muscle wasting occurs. Genetic testing for SMA looks for mutations in the SMN1 gene to confirm a diagnosis.
However, some rare forms of SMA aren’t caused by SMN1 mutations. In this case, a muscle MRI can help point doctors in the right direction. Researchers have found that MRI scans from people with SMA who have SMN1 mutations and those who don’t look very similar. The results from a muscle MRI can help make a final diagnosis.
Many motor neuron diseases share similar symptoms and can be difficult to tell apart. MRI may be one tool the doctor uses to help diagnose SMA and rule out other conditions like muscular dystrophy or amyotrophic lateral sclerosis.
An MRI scan can also be a useful tool for guiding a muscle biopsy. If your doctor needs to take a sample of your muscle tissue, they can use MRI to find the best place to take it.
Weakened muscles from SMA can put extra pressure on joints, including the sacroiliac (SI) joints. These joints connect the spine and the hip bones. People with SMA are at a higher risk of developing SI joint dysfunction, impairment, and inflammation, which causes pain and mobility issues.
SI joint dysfunction is difficult to diagnose because it shares symptoms with other conditions that cause hip and lower back pain. Your doctor can perform a physical exam and some mobility tests during the diagnostic process.
MRI may be useful for finding the cause of lower back pain. It can provide detailed images of your muscles and joints, helping your doctor make a diagnosis. An MRI scan will show if you have sacroiliitis (inflammation) or other SI joint issues.
In the last decade, the U.S. Food and Drug Administration (FDA) has approved three new therapies for the treatment of spinal muscular atrophy:
Doctors and researchers determine whether an SMA treatment works by tracking changes in motor function, mobility, and the ability to reach developmental milestones. Examples include the six-minute walk test and the Hammersmith Functional Motor Scale Expanded, which may help a care team better identify abnormalities.
MRI scans can also give an inside look into what’s happening to a person’s nerve cells and muscles while they’re being treated. In SMA, muscle tissue wastes away and is replaced with fat — especially in the arms. A spine and muscle MRI can give doctors a closer look at whether SMA treatments are effective.
One small study followed three adults who were diagnosed with SMA type 3. They were treated with nusinersen and then had MRI scans taken of their thigh muscles and cervical spinal cord (the neck area). This study showed that MRI scans may be helpful for seeing small changes in the body during treatment.
While the concept is promising, larger studies with more participants — like clinical trials — are needed to confirm whether this is effective.
On mySMAteam, the social network for people with SMA and their loved ones, more than 2,300 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.
Have you had an MRI scan? How was the process for you? Share your experience in the comments below, or start a conversation by posting on your Activities page.