Axonal injury within language network in primary progressive aphasia

Area of Science:

• Neuroimaging
• Neurology
• Biochemistry

Background:

• Primary progressive aphasia (PPA) involves progressive language impairment due to left hemisphere pathology.
• Understanding the neurobiological underpinnings of PPA is crucial for diagnosis and treatment.

Purpose of the Study:

• To investigate axonal fiber integrity in perisylvian language areas in PPA using in vivo proton magnetic resonance spectroscopy (1H-MRS).
• To differentiate PPA from Alzheimer's disease (AD) based on brain metabolite profiles.

Main Methods:

• 1H-MRS was employed to measure brain metabolites (NAA, mI, choline, creatine) in the superior longitudinal fasciculus (SLF) of PPA patients, AD subjects, and controls.
• Metabolite ratios (NAA/Cr, mI/Cr, choline/Cr) were analyzed bilaterally within the SLF, a key language pathway.

Main Results:

• PPA patients exhibited an asymmetrical reduction in the N-acetylaspartate to creatine (NAA/Cr) ratio, predominantly on the left side, compared to AD and controls.
• An increased myoinositol to creatine (mI/Cr) ratio was observed bilaterally in the PPA group versus controls.
• No significant differences in the choline to creatine (choline/Cr) ratio were found among the groups.

Conclusions:

• The findings suggest asymmetrical, focal axonal injury within the language network in PPA.
• 1H-MRS metabolite ratios, particularly NAA/Cr, show potential as a biomarker to distinguish PPA from AD.