Objective: To evaluate the diagnostic value of combined acute levodopa challenge and olfactory testing to predict PD diagnosis.

Background: Acute levodopa challenge can be used to predict sustained long-term dopaminergic response and support a possible diagnosis of Parkinson’s disease (PD). Olfactory testing is often used in clinical practice, as hyposmia is a nonmotor feature of PD that can precede motor symptoms by several years. The combination of both to predict sustained long-term dopaminergic response was not previously evaluated.

Methods: We conducted a retrospective review of medical records from patients with recent onset of parkinsonism that were submitted to acute levodopa challenge for clinical prediction of sustained long-term dopaminergic response and that underwent olfactory testing with Sniffin’ Sticks Test (SST). Patients with at least two years of follow-up were included. When a minimal 24% improvement was not reached, acute levodopa challenge was rated negative. Sensitivity (Se), specificity (Sp), positive and negative predictive values (PPV; NPV) and likelihood ratios (LR+; LR-) together with diagnostic effectiveness (Accuracy), and Youden’s index (‘J’) were calculated for the acute levodopa challenge in combination with three olfaction variables: hyposmia by SST total score (HypTot), hyposmia by identification subscore (HypIdent) and anosmia by SST total score (AnTot).

Results: Two hundred and ten patients (157 PD and 53 non-PD) were included: 113 patients were rated as positive on acute levodopa challenge, which was 70.1% sensitive and 94.3% specific for predict sustained long-term dopaminergic response, showing PPV=97.3%; NPV=51.5%; LR+=12.3; LR-=0.32; Accuracy=76.2% and J=0.64. Combination of acute levodopa challenge and olfactory testing enhanced sensitivity for all three olfactory variables (HypTot=90.4%, HypIdent=90.4%, AnTot=83.4%) and also improved NPV (HypTot=72.2%, HypIdent=71.2%, AnTot=62.3%). Diagnostic power as evaluated by Accuracy (HypTot=86.2%, HypIdent=85.2%, AnTot=82.9%) and ‘J’ (HypTot=0.64, HypIdent=0.60, AnTot=0.65) showed improvements in the combination performance.

Conclusions: The combination of acute levodopa challenge and hyposmia by SST total score, enhances the sensitivity and accuracy for predicting sustained long-term dopaminergic response as a major ancillary criteria for PD diagnosis.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/diagnostic-value-of-combined-acute-levodopa-challenge-and-olfactory-testing-to-predict-parkinsons-disease-diagnosis/