Negative DAT-SPECT in Old Onset Parkinson's Disease: An Additional Pitfall?

Area of Science:

• Neurology
• Neuroimaging
• Geriatrics

Background:

• Scans without evidence of dopaminergic deficit (SWEDDs) describe patients with Parkinson's disease (PD) clinical symptoms but normal dopamine transporter single-photon emission computed tomography (DAT-SPECT) findings.
• The interpretation of SWEDDs is debated, with recent research suggesting DAT-SPECT may not accurately reflect nigral cell bodies or striatal fibers.
• Compensatory downregulation of dopamine transporters (DAT) in early PD appears less effective in older-onset patients compared to young-onset patients.

Observation:

• Eight elderly-onset patients with clinical parkinsonism and positive levodopa response presented with normal visual and semiquantitative DAT-SPECT scans.
• Two of these patients later showed abnormal DAT-SPECT results upon repeat scanning.

Findings:

• Elderly-onset Parkinson's disease patients may present with true dopaminergic degeneration despite normal initial DAT-SPECT findings.
• This discrepancy is potentially explained by less efficient striatal compensatory strategies in older individuals diagnosed at early PD stages.
• Normal DAT-SPECT in older patients might reflect an early disease stage before significant dopaminergic deficit is detectable via imaging.

Implications:

• Re-evaluation of diagnostic criteria for SWEDDs in the elderly population is warranted.
• Consideration of age-related compensatory mechanisms may improve the diagnostic accuracy of DAT-SPECT in Parkinson's disease.
• Further research into the neurobiological underpinnings of SWEDDs in older adults is crucial for tailored treatment strategies.