MRI scan of waste system in brain may track NMOSD severity, progression
Study: Lower values of imaging marker associated with greater disability
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A specialized MRI measure used as a proxy of the brain’s waste-clearing system may help monitor disease severity and progression in people with neuromyelitis optica spectrum disorder (NMOSD), according to a new study.
NMOSD patients had significantly lower values of the imaging marker, called diffusion tensor imaging (DTI) analysis along the perivascular space (DTI-ALPS) index, compared with healthy individuals. Also, lower DTI-ALPS index values were significantly associated with greater disability and longer disease duration in people with NMOSD.
“This study demonstrates that the DTI-ALPS index is a sensitive and clinically relevant exploratory marker,” and highlights “the potential of this metric to track the cumulative impact of NMOSD-specific [damage],” researchers wrote.
The study, “Evaluation of the DTI-ALPS index in neuromyelitis optica spectrum disorder: a cross-sectional study of its correlation with disease duration and disability,” was published in Neuroradiology.
MRI scans essential for diagnosing NMOSD
NMOSD is a neurodegenerative condition characterized by inflammation and damage to the spinal cord and the optic nerves, which carry signals between the eyes and the brain. It is typically marked by relapses, or sudden periods of new or worsening symptoms.
Most patients have self-reactive antibodies that target aquaporin-4 (AQP4), a water-channel protein highly present in neuron-supporting cells called astrocytes that helps maintain fluid balance in the brain and spinal cord.
MRI scans help visualize abnormalities in the brain, optic nerves, and spinal cord. They are essential for diagnosing NMOSD and differentiating it from multiple sclerosis (MS), another neurodegenerative condition marked by inflammatory attacks on certain parts of the brain and spinal cord.
DTI, an MRI imaging technique that measures the movement of water molecules in tissue, has “emerged as a valuable tool for studying microstructural changes in the brain and spinal cord in patients with NMOSD,” the researchers wrote. It “is used to detect subtle alterations in areas that may appear normal on conventional MRI, thus enhancing the ability to diagnose and monitor the disease at an earlier stage.”
DTI-ALPS, which tracks water movement along fluid-filled spaces surrounding blood vessels that serve as drainage pathways, has been mainly used as an indirect way of evaluating the function of the glymphatic system, the brain’s waste-clearance system.
“Given that AQP4 water channels are the primary facilitators of glymphatic flow, their disruption in NMOSD may lead to ‘glymphatic failure’ —a [disease-associated] state increasingly recognized as a final common pathway for cumulative tissue injury and neurodegeneration in several [brain and spinal cord] disorders,” the researchers wrote.
NMOSD patients had much lower DTI-ALPS values than healthy controls
In this study, a team of researchers in Brazil set out to evaluate the utility of the DTI-ALPS index as an imaging marker for assessing clinical disability and disease progression in people with NMOSD.
To do so, they analyzed DTI-ALPS data from 21 NMOSD patients (most with anti-AQP4 antibodies), 34 age- and sex-matched healthy controls, and 42 individuals with relapsing-remitting MS (RRMS), a specific type of MS also marked by relapses.
Results demonstrated that people with NMOSD had significantly lower DTI-ALPS values compared with healthy controls — “a finding mirrored in the MS group,” the team wrote. However, no significant differences were observed between the NMOSD and RRMS groups.
[These results] indicate that DTI-ALPS can serve as a sensitive group-level imaging marker for NMOSD-related tissue alteration.
In the NMOSD group, lower DTI-ALPS values were significantly associated with more severe disease, as assessed by the Expanded Disability Status Scale, “suggesting that DTI-ALPS decline mirrors cumulative neurodegeneration in this group,” the researchers wrote.
Similarly, lower index values were significantly associated with a longer disease duration of more than five years in people with NMOSD.
However, no such associations were observed in people with RRMS, “indicating that this specific imaging marker tracks with different disability drivers in NMOSD versus RRMS,” the team wrote.
These differences may reflect the distinct biology of NMOSD, in which damage to AQP4-positive astrocytes could have a greater impact on fluid movement around brain blood vessels.
These results “indicate that DTI-ALPS can serve as a sensitive group-level imaging marker for NMOSD-related tissue alteration,” the team wrote. “Practically, ALPS is relatively simple to compute from a standard DTI acquisition and could be integrated into … MRI protocols as a complementary metric.”
However, the researchers noted that “the application of the DTI-ALPS index in NMOSD diagnosis is still in its early stages” and should currently be considered an exploratory marker rather than a diagnostic test.
“Future longitudinal studies, tracking the same patients over multiple years, are required to confirm whether the DTI-ALPS index can serve as a predictive marker for clinical worsening,” they concluded.
