NEFL and Alzheimer disease: Neurosurgeons often pay close attention to serum NfL levels because they reflect the activity of certain neurological diseases, including Alzheimer’s disease, stroke, small vessel disease, and head trauma (19, 33, 34) used intraepidermal nerve fiber density quantification to evaluate the occurrence and progression of peripheral neurotoxicity and reported that serum NfL levels are correlated with the severity of structural and functional changes in axons (35).