Whole-body MRI boosts certainty of ALS diagnosis, study finds
Assessing muscle swelling from scans improves accuracy
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- Whole-body MRI (WB-MRI) may improve ALS diagnostic certainty.
- WB-MRI assesses muscle swelling (edema) as a marker for lower motor neuron dysfunction.
- This method can reclassify possible/probable ALS cases to definite diagnoses.
Incorporating muscle assessments from whole-body MRIs (WB-MRIs) into the diagnostic process for amyotrophic lateral sclerosis (ALS) may help identify the condition with a greater degree of certainty, according to a study from France.
ALS causes damage to specialized nerve cells called motor neurons. Some criteria for diagnosing ALS require signs of problems with the motor neurons that run from the brain to the spinal cord (upper motor neurons, or UMNs) and those that run from the spinal cord to muscles (lower motor neurons, or LMNs). However, it can be difficult to identify LMN involvement with common diagnostic techniques, reducing the certainty of diagnosis.
The researchers found that assessing muscle swelling (edema) on WB-MRI can improve the detection of LMN dysfunction and increase the certainty of an ALS diagnosis.
“These findings suggest that muscle edema may represent a relevant surrogate marker of LMN involvement for integration into MRI-based diagnostic assessment of ALS,” they wrote.
The study, “Whole-body muscle MRI improves diagnostic certainty in amyotrophic lateral sclerosis,” was published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration.
Complex diagnosis
Diagnosing ALS is often complex because there is no definitive biological marker of the condition. One commonly used diagnostic framework is the Awaji criteria, which classify a case as possible, probable, or definite ALS depending on the amount of evidence. This includes evidence of UMN and LMN dysfunction.
The main method for testing LMN dysfunction is electromyography (EMG), which measures the electrical activity of muscles at rest and with movement. Because the technique is invasive, only a limited number of muscles are assessed, potentially underestimating LMN involvement.
WB-MRI may provide an alternate method for assessing LMN dysfunction. Unlike EMG, which requires separate testing for each muscle, WB-MRI captures data from muscles throughout the body.
The researchers set out to test whether adding WB-MRI to the diagnostic workup improved the diagnostic certainty in 47 people with suspected ALS.
When using only information from a neurological examination and EMG, the team classified 51.1% of cases as possible ALS, 40.4% as probable ALS, and 8.5% as definite ALS based on the Awaji criteria. Over two years of follow-up, no alternative diagnoses emerged for any participants, supporting the ALS diagnosis.
Next, the researchers used WB-MRI data to complement clinical assessments and EMG and repeated the classification process. They considered muscle edema (swelling due to fluid buildup) and fatty infiltration (replacement of muscle cells with fat cells) signs of potential LMN dysfunction.
When edema and fatty infiltration were both required as evidence of LMN problems, the diagnostic certainty increased for about 15% of participants. This included possible cases redefined as probable or definite and probable cases redefined as definite.
When only muscle edema was considered, the diagnostic certainty increased for about one-quarter of cases. After this reclassification, 17% of participants had a definite ALS diagnosis.
“The addition of MRI findings as a surrogate marker of LMN involvement resulted in a shift toward higher diagnostic categories,” they wrote.
Additional analyses showed that edema tended to correlate with signs of LMN problems on EMG. However, it also identified areas of potential LMN dysfunction that EMG did not catch, suggesting that swelling may reflect early patterns of nerve loss in ALS.
In contrast, fatty infiltration had low correlations with EMG findings. This could reflect more advanced muscle involvement, according to the team.
Based on these findings, they concluded that muscle edema is likely a more useful metric in the ALS diagnostic process.
The study had several limitations. For example, WB-MRI analyses relied on clinician judgment rather than quantitative metrics, which could influence results. And while edema could be a marker of LMN dysfunction, it isn’t necessarily specific to ALS.
“Muscle edema should be interpreted cautiously and within the appropriate clinical and electrophysiological context rather than as evidence of disease specificity,” the researchers wrote.
The scientists recommended that future studies attempt to replicate these findings in larger groups of participants from more clinical centers. Further research could also help determine if WB-MRI provides useful information for monitoring ALS progression or predicting prognosis, they said.
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