"A new blood test may be as accurate as a test requiring a painful spinal tap for differentiating Parkinsons disease from similar disorders according to a study httpneurology.orglookupdoi.WNL. published Wednesday in Neurology the medical journal of the American Academy of Neurology. Parkinsons 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 Parkinsons disease are called atypical parkinsonism disorders.  Many doctors cannot tell whether a patient has Parkinsons disease or atypical parkinsonism.  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 said Dr. Oskar Hansson lead author of the new study a neurologist and an associate professor at Lund University in Sweden.  Nonspecialists do not really know exactly what questions to ask the patient and the special signs to look for Hansson wrote in an email. Yet patients with atypical disorders usually have a much worse prognosis with faster disease progression with more disabling symptoms than Parkinsons patients so early identification is crucial.  The correct diagnosis is also key to treatment since most patients with atypical parkinsonism disorders do not respond well to dopaminetargeting medications that are usually prescribed for Parkinsons patients Hansson said.  Validating a new biomarker 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. When validating a new biomarker for disease one should always analyze at least two different groups of patients and controls to make sure that the results are reproducible said Hansson who added that participants should also include both early and latestage patients established at different clinics. All told a total of  people with Parkinsons and  healthy volunteers serving as a comparison group participated in Hanssons study along with  patients with atypical parkinsonism disorders.  Of these  patients had multiple system atrophy which impairs the bodys 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  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 Parkinsons 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  and a specificity of  while in the United Kingdom sensitivity was  and specificity . For earlystage study participants generally sensitivity was  and specificity was . Overall the blood test showed equal accuracy as the spinal fluid test when diagnosing Parkinsons or an atypical parkinsonism disorder in both early and later stages of disease.  Hansson imagines that bloodbased tests will be used in the future in the diagnostic workup of patients with parkinsonism by most doctors who are not very specialized with these movement disorders. He also believes the test will be used by specialists for Parkinsons patients who do not exhibit a very typical symptomatology or do not respond as expected to treatment.  Misdiagnosis is common The prevalence of Parkinsons in the general population increases from about  at age  to  by age  according to the Centers for Disease Control and Prevention https_view.htm. Atypical parkinsonism disorders are not as common as Parkinsons disease said Dr. Jeff Bronstein a professor of neurology and director of movement disorders at David Geffen School of Medicine at UCLA. He was not involved in the new study. Usually patients are first diagnosed with Parkinsons and only later do their doctors discover that they have one of the more rare neurodegenerative atypical parkinsonism disorders which are most likely to affect people in their s and s and represent approximately  to  of all cases originally diagnosed as Parkinsons httpjournals.plos.orgplosonearticleid.journal.pone.. Though atypical parkinsonism conditions look very similar to Parkinsons at first they have a different underlying molecular cause according to Bronstein and so it is important to recognize them early in order to treat them properly. Diseasespecific therapies are now in trials so accurate diagnosis is essential in determining if these new treatments work he said. According to Dr. Paul Wright chairman of neurology at North Shore University Hospital in Manhasset New York and Long Island Jewish Medical Center in New Hyde Park New York the importance of this study is that it brings to light that there are new biomarker tests that can delineate between these neurological diseases. A lot of time people come in and say they or a family member has a tremor and they believe its Parkinsons disease said Wright who also was not involved in the study. This early assumption may impede diagnosis of a less recognized atypical parkinsonism condition.  Or a patient has horrible blood pressure fluctuations Wright said and no obvious tremor or rigidity symptoms so a doctor suspects a heart condition. Instead the cause is multiple system atrophy a neurodegenerative disease. Though other symptoms will show up eventually and help in diagnosing the patient in the meantime the patient will be receiving the wrong medicines. An accurate blood test then would be good news in these situations. Its a lot more reassuring to a patient to say were just going to take a blood test to check for a few things  Wright said. Its much easier and less anxietyprovoking for patients than taking a spinal tap. Up until now many diseases have been diagnosed based on symptoms with patients asking How do you know I have this Meanwhile doctors are not always correct Wright said. This is true even of Parkinsons which is diagnosed based on symptoms a patients history neurological exams a patients response to medicine and in some cases brain imaging tests.  Still Wright is hopeful and believes a biomarker test for Parkinsons will be down the line. ... In general researchers are looking for biomarkers of disease.  Specialists and subspecialists are available only in big cities Wright said and access to a simple blood test would enable a correct diagnosis in a primary care office. We always assume theres luxury Wright said. But thats not really whats real in most of the country."