To develop quantitative spatiotemporal measures of finger tapping in idiopathic Parkinson’s disease (PD).

Motor blocks occur in Parkinson’s disease (PD) patients during speech, upper limb movements (such as handwriting and finger tapping) and gait. While freezing of gait (FOG) has been extensively studied, difficulty with manual dexterity, often precedes gait dysfunction. Quantitative measures of upper limb function could allow earlier detection of freezing of the upper limb (FOUL).

25 HC and 54 PD patients (25 noFOG and 29 FOG) were analyzed. Age and MoCA were similar between PD groups while disease duration was longer and UPDRS scores higher in the FOG group. 50% noFOG and 63% FOG subjects showed FOUL, compared to only 6% of FOG with visualized freezes during gait assessments. Finger tapping velocity was faster (HC 1.5±0.9, noFOG 1.3±0.5, FOG 1.8±0.8 taps/s; p=0.031 noFOG vs FOG), percent variability in intertap interval was higher (HC 21±14, noFOG 20±14, FOG 30±18; p=0.045), tapping amplitude was smaller (HC 153±57, noFOG 168±45, FOG 116±53 degrees; p=0.007) and variability in amplitude higher (HC 23±15, noFOG 21±16, FOG 34±22; p=0.013) in FOG subjects, correcting for multiple comparisons. Inter-tap interval while shorter in the FOG group (noFOG 0.9±0.3, FOG 0.7±0.3 s; p=0.018), was not significant after accounting for multiple comparisons.

FOUL was seen in 50% of noFOG subjects whereas FOG subjects showed greater impairment in spatiotemporal finger tapping dynamics compared to noFOG, akin to that seen in gait. This could serve as an early marker for motor freezing.