Istradefylline effects on tremor dominance (TD) and postural instability and gait difficulty (PIGD).

Background: In patients with Parkinson's Disease (PD), two distinct motor subtypes, tremor dominant (TD) and postural instability and gait difficulty (PIGD), can be differentiated using Unified Parkinson's Disease Rating Scale (UPDRS) sub-scores. This post hoc analysis of pooled data from eight pivotal studies examined the effect of treatment with istradefylline, a selective adenosine A2A receptor antagonist, on these subtypes. Methods: In eight randomized, placebo-controlled phase 2b/3 trials, patients on levodopa with carbidopa/benserazide experiencing motor complications received istradefylline (20 or 40 mg/day) or placebo for 12 or 16 weeks. TD subtype was defined by the UPDRS II/III items kinetic and postural tremor in right/left hand and (resting) tremor in the face, lips, chin, hands, or feet; PIGD items were freezing, walking, posture, gait, and postural instability. The ratio of mean scores from TD:PIGD items determined subtype (TD [TD:PIGD ratio ≥ 1.5], PIGD [TD:PIGD ratio ≤ 1.0], mixed-type [ratio 1-1.5]). Results: In total, 2719 patients were included (PIGD, n = 2165; TD, n = 118; mixed-type, n = 188; not evaluable, n = 248). Among TD subtype patients, the least-squares mean change from baseline versus placebo in UPDRS II/III TD-related total score was significant at 20 mg/day istradefylline (-2.21; 95 % CI, -4.05 to -0.36; p = 0.02). For PIGD subtype patients, there was a significant difference from placebo in UPDRS II/III PIGD-related total score at 40 mg/day istradefylline (-0.25; -0.43 to -0.06; p = 0.01). Conclusions: The data from this analysis of UPDRS-based motor subtypes suggest that istradefylline can improve motor disability in PD patients with motor fluctuations regardless of PD subtype. Future research should characterize the effects of istradefylline on tremor.