Researchers have found that people with Parkinson’s disease (PD) have lower levels of a certain protein in their blood than people with similar diseases. The results suggest that testing for the protein might help doctors to accurately differentiate between PD and similar diseases early on. The study appears in the February 8 online edition of Neurology.
Because there are no definitive diagnostic tests for Parkinson's, the diagnosis can be unclear especially early on in the disease. When diagnosis is uncertain, some people may be diagnosed with “parkinsonism," which refers to a category of diseases, including Parkinson's, that cause slowness of movement, stiffness and rest tremor. Other diseases in the category include multiple system atrophy (MSA), progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD).
Earlier studies found that a spinal fluid test may help distinguish PD from these other diseases, but this test is difficult to do during a routine visit to the doctor.
For the new research, scientists led by Oskar Hansson, M.D., Ph.D., at Lund University in Sweden, developed a blood test for a protein called neurofilament light chain protein (NfL) — the same protein detected by earlier spinal fluid tests. Then they used it to analyze blood samples from 244 people with PD, 88 with MSA, 70 with PSP, 23 with CBD and 79 healthy individuals. Most study participants had been living with their diseases for four to six years, but a subset had been diagnosed within the previous three years. Study participants included those from hospitals in Sweden and in London, UK.
- Blood levels of NfL protein were generally lower in people with PD and in healthy individuals than in people with other Parkinsonian disorders.
- This result held both for those recently diagnosed and those who had been living with their disease for four to six years.
- The test for NfL could not distinguish between MSA, PSP and CBD.
What Does It Mean?
Distinguishing between Parkinson’s and Parkinson’s Plus Syndromes can be difficult, especially in the early stages of disease. When doctors are unsure if the symptoms of rigidity, slowness of movements and tremor are classic PD or a Parkinson’s Plus syndrome, they may diagnose a person with “parkinsonism.” Over time, as symptoms progress, the diagnosis will become clearer.
The current study suggests that in cases of uncertainty, blood levels of NfL may help the doctor determine if a person is living with PD or a PD plus syndrome. It’s important to note that levels of blood NfL were similar between people with PD and controls, which means this blood test isn’t useful for diagnosing Parkinson’s disease overall, but simply for differentiating it from similar diseases.
In addition, having an accurate blood test could help to improve clinical trials. It’s thought that some promising clinical trials fail because participants are incorrectly diagnosed. A blood test would solve this issue.
Lastly, if we are able to develop drugs to slow or stop PD, a simple test to distinguish PD from parkinsonisms would help identify people who would benefit from disease-specific treatments. It’s important to note that this blood test studied was only for those living with parkinsonisms. The search is still on for a simple blood test or biomarker that can distinguish people with PD from healthy individuals.
Hansson O, Janelidze S, Hall S, et al. (2017). Blood-Based NfL: A Biomarker for Differential Diagnosis of Parkinsonian Disorder. Neurology 88: 1-8
Alves G, Bonanni L. (2017). Neurofilament Light: A Heavyweight Diagnostic Biomarker in Neurodegenerative Parkinsonism? Neurology 88: 1-2