Early detection of diseases that result in degeneration of nerve cells in the brain and spinal cord as well as damage that might follow trauma (e.g., a concussion) is important for initiation of interventions with the potential to improve patient outcomes.  Direct access to the central nervous system is possible, but it is not practical as part of routine patient evaluation or monitoring. As a result, we have depended in imaging techniques, such as computed tomography and magnetic resonance imaging, for assessment of degenerative changes in the brain.  These methods are valuable, but may not be sufficiently sensitive to detect subtle early changes and they are also expensive to use. Neurofilaments help form the structure of nerve cells and damage to these cells results in release of the molecules that comprise neurofilaments into the cerebrospinal fluid (the watery substance that bathes the brain and the spinal cord) and from there into the blood. Thus, a simple test using a blood sample can detect elevated levels neurofilament proteins, a clear  sign of nerve cell damage.

One particular molecule called neurofilament light chain (NfL) has proven to be very useful for detecting neurodegeneration, monitoring its progression, and evaluating the effects of treatment.  NfL is elevated in patients with a wide range of neurologic diseases, including multiple sclerosis, Alzheimer’s disease, Parkinson disease, as well as in individuals with chronic traumatic encephalopathy (CTE), a neurodegenerative disease caused by repeated head injuries. It is also elevated in the blood of patients with very rare neurodegenerative diseases, such as spinal muscular atrophy and hereditary transthyretin-related amyloidosis. Most important elevations in blood levels of NfL may be detected long before symptoms of neurologic disease become apparent. For example, results from one study of patients being monitored because of high risk for early onset Alzheimer’s disease showed that elevations in NfL occurred 16 years prior to the onset of symptoms.  It has also been demonstrated that effective therapy, for example in patients with multiple sclerosis, lowers blood NfL levels.  Although the technology is not yet fully developed, we may soon see real-time analysis of NfL levels for many individuals ranging from those at risk of developing Alzheimer’s disease to athletes playing sports with high potential for head trauma. Information gained with this blood test may help clinicians identify early evidence of damage and initiate appropriate medical intervention.