Researchers at the Sant Pau Research Institute in Barcelona have identified early microscopic white matter abnormalities in Alzheimer’s disease patients using a specialized neuroimaging metric called peak width of skeletonized mean diffusivity, or PSMD. According to a study published in the journal Alzheimer’s & Dementia, this advanced diffusion magnetic resonance imaging tool detects subtle structural brain changes approximately 15 years before clinical dementia symptoms typically emerge in high-risk populations like adults with Down syndrome.
Detecting Early Microscopic White Matter Changes Via PSMD
Traditional Alzheimer’s research has largely focused on gray matter, where neuronal cell bodies reside and hallmark lesions accumulate. However, findings from the Sant Pau Research Institute indicate that white matter tracts undergo alterations long before conventional MRI scans reveal tissue damage. According to Dr. Alexandre Bejanin, head of the Neuroimaging of Aging and Neurodegenerative Diseases research group at IR Sant Pau and corresponding author of the study, white matter is altered early in the disease process and provides critical information regarding progression.
The research team analyzed 496 participants drawn from two distinct Sant Pau cohorts: the Down-Alzheimer Barcelona Neuroimaging Initiative and the Sant Pau Initiative on Neurodegeneration. The sample comprised 150 cognitively healthy individuals, 118 patients with sporadic Alzheimer’s disease, and 228 adults with Down syndrome. By utilizing diffusion magnetic resonance imaging, the investigators measured the randomized movement of water molecules through brain tissue to calculate PSMD values.
Did you know? PSMD isolates white matter tracts to generate a single summary value per individual. This streamlines data calculation and makes the metric practical for research settings, clinical trials, and future diagnostic protocols, according to study lead author Dr. Alejandra Morcillo-Nieto.
Down Syndrome as a Predictable Genetic Model for Alzheimer’s
Adults with Down syndrome provide a unique window into the preclinical phases of neurodegeneration. Trisomy 21 involves an extra copy of the amyloid precursor protein gene, which drives excess beta-amyloid production. Consequently, individuals with Down syndrome face a very high lifetime risk of developing Alzheimer’s disease alongside early cerebral amyloid angiopathy, a vascular condition driven by amyloid deposits in brain blood vessels.
“Down syndrome offers us a unique opportunity to study the earliest stages of Alzheimer’s disease because its biological progression is more predictable,” Dr. Bejanin notes. Within this cohort, PSMD values began showing notable deviations compared to control groups at approximately age 38. This shift occurs roughly 15 years prior to the typical clinical onset of Alzheimer’s dementia.
Multifactorial Origins of White Matter Damage
To uncover the biological drivers behind these microstructural shifts, the research team compared PSMD metrics against several cerebrospinal fluid biomarkers. The most consistent correlation emerged with neurofilament light chain, a protein released directly into fluid when axonal damage occurs. Additional associations linked PSMD with traditional Alzheimer’s indicators such as beta-amyloid, tau proteins, and markers reflecting glial activation and neuroinflammation.
According to Dr. Morcillo-Nieto, white matter destruction stems from an intricate web of biological pathways rather than a solitary trigger. Alzheimer’s pathology, cerebral amyloid angiopathy, and small vessel disease interact continuously. While the study effectively links elevated PSMD values to poorer cognitive performance across both sporadic cases and Down syndrome cohorts, researchers emphasize that longitudinal studies are necessary to confirm whether these white matter shifts directly predict subsequent clinical decline.
Frequently Asked Questions
What is PSMD in neuroimaging?
PSMD stands for peak width of skeletonized mean diffusivity. It is a diffusion MRI metric that analyzes water molecule movement to detect microscopic damage within the brain’s white matter tracts before conventional scans show visible lesions.
Why is Down syndrome studied in Alzheimer’s research?
Trisomy 21 includes an extra copy of the APP gene, leading to accelerated beta-amyloid accumulation. This predictable trajectory allows scientists to observe early biomarker changes decades before symptom onset.
Can PSMD diagnose Alzheimer’s disease on its own?
No. Researchers view PSMD as a complementary biomarker rather than a standalone diagnostic test, designed to help clinicians monitor white matter integrity alongside established disease markers.
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