The role of autonomic testing in the differentiation of Parkinson's disease from multiple system atrophy

Abstract

Differentiation of idiopathic Parkinson's disease (PD) from multiple system atrophy (MSA) can be difficult. Methods devised to help distinguish the two disorders include standardized autonomic testing and cardiac imaging with iodine-123 meta-iodobenzylguanidine myocardial scintigraphy. MSA patients had more severe adrenergic and overall autonomic dysfunction when compared to control and PD patients. Area of anhidrosis on thermoregulatory sweat test was greater in MSA (67.4±12.42, p<0.001) versus PD patients (area of anhidrosis, 1.7±2.96). Postganglionic cardiac sympathetic innervation (iodine-123 meta-iodobenzylguanidine) expressed as heart to mediastinal ratio was significantly lower in Parkinson's disease patients (1.4±0.40, p=0.025) compared to controls (2.0±0.29), but not in multiple system atrophy (2.0±0.76). These findings indicate that autonomic dysfunction is generalized and predominantly preganglionic in multiple system atrophy, and postganglionic in Parkinson's disease. In our hands the thermoregulatory sweat test provides the best distinction between MSA and PD. However further confirmatory studies using larger patient numbers are required. Currently a combination of clinical judgment and autonomic testing is recommended to help differentiate MSA and PD.

Figure 1. Comparison of specific autonomic tests in the differentiation of control, PD and MSA patients

CASS scores for all three groups (control n=10; PD n=10; MSA n=9) are broken down into adrenergic (A), and CASS total (B) scores. MSA patients exhibited significantly higher adrenergic and overall autonomic dysfunction compared to controls and PD patients as shown by their respective CASS scores (Kruskal–Wallis one-way analysis of variance, *p<0.001 for both CASS adrenergic and CASS total scores). There was a significant increase in % anhidrosis on TST in MSA (n=9) versus PD (n=8) patients (C; Mann-Whitney U test, *p<0.001). Heart to mediastinal (H/M) ratios for I¹²³ MIBG uptake at 4 hours (D) are shown for control (n=10), PD (n=10) and MSA (n=9) groups. Cardiac uptake of I¹²³ MIBG was significantly reduced as indicated by lower H/M ratios for PD patients versus controls (Kruskal–Wallis one-way analysis of variance, *p=0.025). There were no significant differences in I¹²³ MIBG uptake when comparing MSA to PD or control groups. Data are expressed as scatter plots with each individual symbol representing a single patient and the horizontal line representing the mean of the corresponding group.