Combined DaT imaging and olfactory testing for differentiating parkinsonian disorders.

Area of Science:

• Neurology
• Nuclear Medicine
• Diagnostic Imaging

Background:

• Dopamine transporter (DaT) imaging using single photon emission computed tomography (SPECT) is highly sensitive for detecting striatal dopaminergic denervation.
• Distinguishing idiopathic Parkinson's disease (iPD) and dementia with Lewy bodies (DLB) from atypical parkinsonian disorders (aPD) remains challenging with DaT imaging alone.
• Olfactory dysfunction (hyposmia) is common in iPD/DLB but typically absent in aPD, offering a potential complementary diagnostic marker.

Purpose of the Study:

• To evaluate the diagnostic power of combining DaT imaging and olfactory testing in differentiating iPD/DLB from aPD.
• To assess the predictive value of olfactory status in patients with abnormal DaT SPECT findings.

Main Methods:

• A cohort of 129 patients underwent baseline [123I]FP-CIT SPECT (DaT imaging) and olfactory testing.
• Patients were followed clinically for approximately 30 months, with final diagnosis serving as the gold standard.
• A control group of 24 healthy individuals provided normative olfactory and DaT imaging data.

Main Results:

• DaT imaging alone demonstrated high diagnostic performance, with 98% sensitivity and 98% specificity for dopamine-deficient disorders.
• Combined DaT imaging and olfactory testing correctly classified 91% of patients as iPD/DLB, with a positive predictive value (PPV) of 91%.
• The PPV for iPD/DLB increased to over 97% in patients with hyposmia; however, only 45% of aPD patients were correctly classified by the combined approach, partly due to normosmic iPD patients.

Conclusions:

• In patients with abnormal DaT SPECT, the presence of hyposmia significantly increases the likelihood of an iPD/DLB diagnosis to over 90%.
• Conversely, normal olfaction (normosmia) in the context of an abnormal DaT scan only raises the likelihood of aPD to approximately 50%.
• Combining DaT imaging with olfactory testing enhances diagnostic accuracy for differentiating iPD/DLB from aPD, particularly in hyposmic individuals.