NEFL and Alzheimer disease: A marker of subcortical large‐caliber axonal degeneration (Hoffman et al, 1987; Norgren et al, 2003), CSF levels of NfL are elevated in AD and ever more so in ALS, FTD, and atypical parkinsonian disorders (i.e., PSP, MSA, and CBD) (Khalil et al, 2018) and after acute brain injury (e.g., stroke, traumatic brain injury or cardiac arrest).