A new testing strategy has been proposed to use magnetic resonance imaging (MRI) to first screen patients with REM sleep behavior disorder who are at high risk of progressing to Parkinson’s disease. Rather than performing expensive, highly sophisticated tests on all patients, the approach calls for using MRI, which involves no radiation exposure, to identify a high‑risk group and then conducting additional tests only on those patients who need them.

Professor Joo Eun‑Yeon of the Department of Neurology and Professors Kim Eung‑Yeop and Son Beom‑Seok of the Department of Radiology at Samsung Medical Center, together with Professor Kim Jae‑Rim of Sejong Chungnam National University Hospital, reported that they confirmed the potential of using neuromelanin‑sensitive MRI (NM‑MRI) to screen the risk of Parkinson’s disease in patients with REM sleep behavior disorder. The study findings were published in a recent issue of the international journal “Brain Imaging and Behavior.”

REM sleep behavior disorder is a condition in which a person physically acts out dreams, such as shouting or flailing the arms and legs during sleep. It can be detected at a prodromal stage before the onset of Parkinson’s disease, but not all patients progress to Parkinson’s disease. For this reason, early identification of patients at high future risk of developing Parkinson’s disease has been regarded as an important challenge.

One of the main tests currently used to assess the risk of Parkinson’s disease is dopamine transporter positron emission tomography (PET). However, the test is costly, is available only at a limited number of institutions, and requires the use of radioactive isotopes, making it burdensome to apply to all patients with REM sleep behavior disorder.

The research team therefore focused on neuromelanin‑sensitive MRI as a complementary approach. Neuromelanin is a pigment found within dopaminergic neurons. When dopaminergic neurons are damaged, neuromelanin also decreases, so by analyzing the volume and signal intensity of neuromelanin on MRI, it is possible to indirectly assess the extent of neuronal damage.

The team performed neuromelanin‑sensitive MRI in 66 patients with REM sleep behavior disorder and 30 healthy controls. Based on dopamine PET results, the REM sleep behavior disorder group was divided into 37 patients with abnormal findings and 29 with normal findings, and the two groups were compared.

Analysis showed that only the patients with abnormal findings on dopamine PET had a marked decrease in neuromelanin volume and signal intensity on MRI. In contrast, patients with normal PET results did not show any significant difference compared with healthy controls. These results indicate that neuromelanin‑sensitive MRI may reflect damage to dopaminergic neurons and could be used to identify high‑risk patients who require further sophisticated testing.

The researchers emphasized, however, that these findings do not mean neuromelanin‑sensitive MRI can replace dopamine PET. Rather, they explained, the significance lies in suggesting the potential of a stepwise testing strategy in which MRI is used as an initial screening tool and advanced tests such as PET are performed only in patients with suspected abnormalities.

Professor Son stated, “Neuromelanin‑sensitive MRI has the advantage of allowing repeated testing without concerns about radiation exposure, and it can be performed together with conventional brain MRI.” Professor Kim Eung‑Yeop explained, “We have confirmed its potential use as an imaging biomarker to identify patients who require advanced testing.”

Professor Joo said, “Not all patients with REM sleep behavior disorder progress to Parkinson’s disease,” adding, “It is expected to help enable personalized management by tailoring testing and follow‑up strategies according to each patient’s risk of disease progression.”

Hae‑Jin Choi, Staff Reporter, haehae@donga.com

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