NEFL and Alzheimer disease: This result may have been influenced by the short follow-up time used to define stable MCI (2 years), which may be too abbreviated to verify the benign nature of the so-called stable condition. The finding that plasma NFL concentrations were increased already in prodromal AD is promising because it may render plasma NFL more useful in drug development, which is largely focused on this early stage of AD, as well as in clinical practice because patients with MCI increasingly seek medical evaluation.