SPECT and ultrasound detected subclinical changes typical of early Parkinson’s disease among patients with idiopathic rapid-eye movement sleep behavior disorder (IRBD), which may provide markers to identify patients at increased risk for neurodegenerative disorders, according to a study published in the October edition of Lancet Neurology.
Previous studies have indicated IRBD may be an early predictor of neurodegenerative disorders with more than half of patients developing disorders including Parkinson’s disease. The disorders have a latent period or preclinical stage during which protective or disease-modifying therapies might be most successful. Studying preclinical patients would improve knowledge of disease progression at its earliest stages and allow testing of drugs, shared the research team led by Alex Iranzo de Riquer, MD, of the Hospital Clinic of Barcelona in Spain.
Dopamine transporter (DAT) imaging via SPECT shows decreased striatal uptake indicating substantia nigra hyperechogenicity, and transcranial sonography reveals midbrain hyperechogenicity in early Parkinson’s disease patients. Iranzo and colleagues hypothesized that these neuroimaging findings indicative of early Parkinson’s disease may also occur in IRBD patients who might be at increased risk for neurodegenerative syndromes.
The researchers recruited 43 patients (37 men, with a mean age of 70) with IRBD to undergo 123I-FP-CIT SPECT (DAT) and transcranial sonography in October 2007. They compared SPECT data to 18 healthy controls and TCS data to existing data for 149 age- and sex-matched individuals age 50 years or older.
In March, IRBD participants underwent subsequent DAT imaging and TCS studies, and movement disorders specialists clinically reassessed the patients to determine if they had developed a neurological syndrome.
The follow-up neuroimaging studies revealed reduced 123I-FP-CIT uptake or substantia nigra hyperechogenicity in 63 percent of IRBD patients. Eight of these 27 patients developed a neurodegenerative disease; five were diagnosed with Parkinson’s disease, two with dementia with Lewy bodies and one with multiple system atrophy. “All eight participants had reduced 123I-FP-CIT uptake or substantia nigra hyperechogenicity at baseline,” reported Iranzo and colleagues.
“Our study shows that decreased binding of 123I-FP-CIT in the striatum or substantia nigra hyperechogenicity can be used to identify individuals with IRBD who are at increased short-term risk for development of … Parkinson’s disease, dementia with Lewy bodies, or multiple system atrophy,” concluded the researchers, who added that the markers can identify abnormalities before the appearance of parkinsonism. They noted a 7 to 8 percent reduction in striatal 123I-FP-CIT uptake in IRBD participants, which suggests a degree of substantia nigra dopaminergic dysfunction lower than the threshold to cause parkinsonism in patients with Parkinson’s disease.
Iranzo noted that extended follow-up and post mortem examination of the IRBD cohort are necessary to confirm the researchers’ theory.