New Imaging Agent Aids in Parkinson's Diagnosis

"We look at Parkinson’s disease as a whole because we don’t know how to separate it, but it’s very likely that within Parkinson’s disease there are some individuals who respond to one drug and not another, and certainly there are individuals who progress more rapidly than others," said Dr. Marek.

"This would be another way to focus treatment more effectively on those who would be more likely to respond to it, if you could identify different biomarkers to identify these subgroups."

There have been other DaT-related tracers that have been used for research over the last 12-15 years in the United States, but it has been difficult to get FDA approval for such agents, because the bar for approval from the FDA’s perspective was to demonstrate that DaT agents were useful as diagnostic tools for Parkinson’s disease, Dr. Marek said in an interview.

However, the agency’s approach to imaging agents has changed in recent years. Manufacturers can now seek indications for imaging agents in four categories: delineation of structure; disease or pathology detection or assessment; functional, physiological, or biochemical assessment; and diagnostic or therapeutic patient management.

DaTscan is indicated for striatal dopamine transporter visualization using SPECT brain imaging to assist in the evaluation of adult patients with suspected parkinsonian syndromes. "That is to say that it is not necessarily a diagnostic tool for Parkinson’s disease, but that it measures dopamine transporter density in the brain and that’s its primary indication," said Dr. Marek. "That distinction enabled the FDA to move ahead more rapidly." DaTscan has been available in Europe since 2000.

Another problem related to its approval is that DaTscan is a derivative of cocaine, so it is classified in the United States as a schedule II drug under the Controlled Substances Act. Radiologists and nuclear medicine physicians working with the tracer will have to be licensed for schedule II drugs by the Drug Enforcement Administration.

Dr. Marek is a consultant for GE Healthcare.