According to a study published recently in the medical journal of the American Academy of Neurology, a new blood test may be as accurate as a test requiring the usual painful spinal tap for differentiating Parkinson’s disease from similar disorders.
Parkinson’s disease is a neurological disorder that can cause tremors, stiffness, slowness of movement, trouble balancing, problems walking and difficulty coordinating movement. Less obvious symptoms include depression, insomnia, anxiety, fatigue and constipation.
Neurological disorders that mimic the symptoms of Parkinson’s disease are called atypical parkinsonism disorders.
Dr. Oskar Hansson, lead author of the new study, a neurologist and an associate professor at Lund University in Sweden says over the years, many doctors find it hard to tell whether a patient has Parkinson’s disease or atypical parkinsonism.
In his words:
‘This can be very challenging, especially during the early stages of the diseases and if the responsible doctor is not a neurologist specialized in movement disorders, non-specialists “do not really know exactly what questions to ask the patient and the special signs to look for,”. Yet patients with atypical disorders” usually have a much worse prognosis, with faster disease progression, (with) more disabling symptoms” than Parkinson’s patients, so early identification is crucial.
Hansson and his colleagues developed a blood test that is, essentially, a variation on an existing test capable of detecting neurofilament light chain protein in spinal fluid. This protein is a component of nerve cells, and when these cells die, it can be detected in both spinal fluid and blood. Because spinal fluid is not easily obtained by a primary care doctor, this diagnostic test is not very useful, so Hansson developed a blood test and investigated its accuracy in the new study.
A total of 244 people with Parkinson’s and 79 healthy volunteers serving as a comparison group participated in Hansson’s study, along with 181 patients with atypical parkinsonism disorders.
Of these, 88 patients had multiple system atrophy, which impairs the body’s involuntary functions such as heart rate, blood pressure and digestion. Seventy patients had progressive supranuclear palsy, which affects movement, walking, balance, speech, swallowing, vision, mood and thinking. And 23 patients had corticobasal degeneration, which causes decreased movement on one side of the body, muscle rigidity, tremor and a disconnection between thought and action.
Testing these participants, the researchers found that nerve protein levels ranged higher in people with atypical parkinsonism and lower in patients with Parkinson’s disease as well as the healthy volunteers. However, the test cannot distinguish between the different atypical disorders, which doctors must rely on symptoms to diagnose.
Blood test accuracy is defined based on sensitivity, the percentage of positives that are correctly identified, and specificity, the percentage of negatives that are correctly identified. In Sweden, the blood test had a sensitivity of 82% and a specificity of 91%, while in the United Kingdom, sensitivity was 80% and specificity 90%. For early-stage study participants, generally, sensitivity was 70% and specificity was 80%.
Overall, the blood test showed equal accuracy as the spinal fluid test when diagnosing Parkinson’s or an atypical parkinsonism disorder, in both early and later stages of disease.