A recent case series report in Movement Disorders examines the potential limitations of dopamine transporter single-photon emission computed tomography (DAT-SPECT) in the diagnosis of Parkinson’s disease, highlighted by cases in which patients with Parkinson’s have scans without evidence of dopaminergic deficit (SWEDDs). Although many SWEDD cases result from a misdiagnosis, others may represent false negatives.
The retrospective review looked at a population of 232 patients with Parkinson’s disease from the movement disorders clinic at the Neurology Unit of Pisa University. All patients met the United Kingdom Parkinson’s Disease Society Brain Bank diagnostic criteria for idiopathic Parkinson’s, however, DAT-SPECT scans were normal in 28 (3.4%).
The study authors focused on 8 of the 28 patients who had a clinical follow-up of at least five years, a clinical confirmation of Parkinson’s, and a normal DAT-SPECT at the time of first observation. The mean age at onset for the 8 cases was 80.8 years. Two patients consented to a repeat DAT-SPECT at three years; both showed abnormal results.
The authors highlight that DAT-SPECT may be unreliable, especially in old-onset Parkinson’s, because the downregulation of DAT that may occur in early Parkinson’s has been shown to be less efficient in patients with old-onset vs young-onset Parkinson’s. Additionally, recent research has called into question the degree of correlation between DAT binding and nigral cell counts.
The study authors conclude that DAT-SPECT, often thought of as the gold standard diagnostic tool, should not be used to definitively rule out Parkinson’s disease and should not significantly affect treatment decisions.