Researchers have discovered a biomarker in cerebrospinal fluid that should help improve diagnosis of Parkinson's disease and dementia with Lewy bodies and distinguish that from other forms of dementia.

An enzyme called DOPA decarboxylase, which plays a crucial role in the production of dopamine in the brain, is present in cerebrospinal fluid at significantly higher concentrations in patients with Parkinson's disease and Lewy body dementia, the researchers found.

This difference is clearly measurable compared with patients suffering from more common Alzheimer's disease, making the test highly specific, the researchers said.

"The importance of this discovery for clinical practice is considerable, as dementia with Lewy bodies is often difficult to diagnose correctly at present,” study leader Dr. Sebastiaan Engelborghs of Vrije Universiteit Brussel said in a statement.

“Because of the strong overlap of symptoms with other forms of dementia, patients are regularly misdiagnosed," he added. "The new measurement method provides doctors with an objective tool for determining the right course of action at an early stage."

The researchers have developed two highly sensitive but still experimental laboratory tests for DOPA decarboxylase. The results of their testing correlated directly with the degree of pathological changes in autopsy samples from patients' brains, they reported in Nature Medicine.

“This publication brings a crucial biomarker closer to the patient, precisely in cases where diagnosis is still too often associated with uncertainty," Engelborghs said.