Severity of parkinsonism associated with environmental manganese exposure

Table 4 Difference in motor outcomes associated with Mn exposure by community, Gauteng province, South Africa, 2016–2020

	Mean difference between Mn smelter community vs. reference community in specified motor outcome (95 % CI)^a
	Unadjusted	Age-adjusted	Fully-adjusted
UPDRS3, total score^b	5.6 (4.1, 7.1)	6.6 (5.2, 7.9)	6.3 (4.9, 7.7)
UPDRS3 subscores^b
Upper limb bradykinesia^c	2.5 (1.8, 3.1)	2.9 (2.2, 3.5)	2.9 (2.2, 3.6)
Upper limb rigidity^d	0.8 (0.5, 1.0)	0.8 (0.6, 1.1)	0.8 (0.5, 1.1)
Lower limb bradykinesia^d	0.5 (0.2, 0.7)	0.6 (0.4, 0.8)	0.6 (0.3, 0.8)
Lower limb rigidity^d	0.8 (0.6, 1.1)	0.9 (0.6, 1.2)	0.9 (0.6, 1.2)
Rest tremor^e	0.1 (-0.01, 0.1)	0.1 (-0.005, 0.1)	0.04 (-0.02, 0.1)
Action tremor^d	0.1 (0.01, 0.2)	0.1 (0.01, 0.2)	0.1 (-0.02, 0.2)
Axial signs^f	0.8 (0.3, 1.3)	1.1 (0.7, 1.6)	1.0 (0.5, 1.5)
Grooved pegboard, time (seconds)^b
Dominant hand	-7.6 (-17.0, 1.9)	1.6 (-7.2, 10.5)	0.9 (-8.2, 10.0)
Non-dominant hand	-4.0 (-14.3, 6.3)	6.9 (-2.6, 16.3)	7.5 (-2.2, 17.1)
Kinematic testing, finger-tapping mean velocity (degrees/second)^b
Dominant hand	-68.4 (-93.9, -43.0)	-74.9 (-101.2, -48.7)	-69.0 (-96.8, -41.3)
Non-dominant hand	-72.8 (-99.6, -46.1)	-82.6 (-110.1, -55.2)	-70.6 (-99.6, -41.6)

Abbreviations: Mn manganese; UPDRS3 Unified Parkinson Disease Rating Scale motor subsection part 3
^a Based on 716 participants (621 in Meyerton and 95 in Ethembalethu). Age adjustment was using age as a continuous variable with natural cubic splines with five knots (5th, 27.5th, 50th, 72.5th, and 95th percentiles) as per Harrell’s placement method [35]. Fully adjusted means adjusted for age, sex, cigarette smoking (ever, former, current), and alcohol use (ever, former, current) (with all results confirmed in models with smoking as a dichotomous variable due to the small number of former smokers)
^b Poorer motor performance is indicated by greater UPDRS3 scores, greater grooved pegboard times, and lower finger-tapping velocities
^c Sum of six UPDRS3 subscores: Finger-tapping, hand rotations, and rapid arm movements for each limb
^d Sum of the two UPDRS3 subscores (one for each limb).
^e Sum of five UPDRS3 subscores: Upper limbs, lower limbs, and face
^f Sum of eight UPDRS3 subscores: Speech, facial expression, neck rigidity, difficulty arising from a chair, posture, gait, postural instability, and global bradykinesia

ISSN: 1476-069X