Objectives: The aim of this study was to evaluate the sensitivity and specificity of various outcomes of acute levodopa challenge test (ALCT) namely improvement of motor function, development of dyskinesia and intolerance; to predict the diagnosis of idiopathic Parkinson's disease (IPD) or Parkinson-plus syndrome; to predict levodopa responsiveness and levodopa-induced dyskinesia (LID) during long-term therapy.
Methods: ALCT was performed on 89 patients with parkinsonism of <2 years and were followed up for 18 months. Improvement of UPDRSm by ≥30% was considered positive.
Results: The test was positive in 37 (43.5%) and negative in 48 (56.5%) of 85 patients completing it. Of the 75 patients completing 18 months' follow-up 34 (45.3%) were diagnosed as IPD. A positive ALCT predicted a clinical diagnosis of IPD with sensitivity and specificity of 97.4% and 70.7% respectively. The predictive value of ALCT for long-term levodopa responsiveness was less than predicting a diagnosis of IPD. While appearance of dyskinesia during ALCT had a low predictive value for future LID (sensitivity 14.3%), it had high predictive value for a diagnosis of multisystem atrophy (MSA) (91% specificity and 37.5% sensitivity). The appearance of symptoms of levodopa intolerance (SLI) during ALCT could predict a clinical diagnosis of MSA with high specificity (95.5%) and moderate sensitivity (50%).
Conclusion: Levodopa responsiveness during ALCT was useful in predicting a diagnosis of IPD but not long-term response to levodopa. The development of dyskinesia during ALCT could not correctly predict LID, but could predict a diagnosis of MSA. The appearance of SLI during ALCT could also predict MSA correctly.
Keywords: Acute levodopa challenge test; idiopathic Parkinson's disease; levodopa responsiveness; levodopa-induced dyskinesia; multisystem atrophy; predictability.