Dopa responsiveness in Parkinson’s disease

<h3>Objectives</h3> To examine serial dopaminergic responses, if there are distinct patterns, and associated factors. <h3>Methods</h3> 1525 challenge tests performed from diagnosis to 12 years in 336 patients in the <i>Parkinson’s Progression Markers Initiative</i> were analysed. ≥ 24.5% improvement in the motor score represented a definite response as defined in diagnostic criteria. Growth-mixture modelling examined for different response patterns, and multinomial logistic regression evaluated for associated factors. <h3>Results</h3> At 1 to 2 years, 48.0% of tests showed a definite response, but this proportion increased with longer duration (51.1-74.3%). We identified 3 treatment-response groups: ‘Striking’ (n = 29, 8.7%), ‘Excellent’ (n = 110, 32.7%) and ‘Modest’ (n = 197, 58.6%). Striking responders commenced treatment earlier (P = 0.02), dopamine agonist monotherapy was less likely (P = 0.01) and they had better cognition (P &lt; 0.01) and ADL scores (P = 0.01). An excellent response was associated with combination therapy (P &lt; 0.01) and higher challenge doses (P = 0.03). <h3>Conclusion</h3> The proportion of PD cases with definite dopa responsiveness increases over time, so the initial treatment response may be an unreliable diagnostic aid.