Longitudinal analysis of glymphatic function in amyotrophic lateral sclerosis and primary lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of motor neurons in the brain and spinal cord. Accumulation of misfolded proteins is central to the pathogenesis of ALS and the glymphatic system is emerging as a potential therapeutic target to reduce proteinopathy. Using diffusion tensor imaging analysis along the perivascular spaces (DTI-ALPS) to assess glymphatic function, we performed a longitudinal analysis of glymphatic function in ALS and compared it to a disorder in the motor neuron disease spectrum, primary lateral sclerosis (PLS). From a cohort of 45 participants from the Calgary site in the CALSNIC study (Canadian ALS Neuroimaging Consortium), including 18 ALS, 5 PLS and 22 control participants, DTI-ALPS was analysed and correlated to clinical features (age, sex, disease presentation, disease severity and progression rate) and white matter hyperintensity burden. This included longitudinal measurements at three time points, 4 months apart. The DTI-ALPS index was reduced in ALS participants compared with PLS and control participants across all three time points. There was no association with clinical factors; however, the index tended to decline with advancing age. Our study suggests heterogeneity in glymphatic dysfunction in motor neuron diseases that may be related to the underlying pathogenesis.