INTRODUCTION: The aim of this study is to show if the exploration of the 
autonomic nervous system is useful to improve the specificity of clinical 
criteria of Parkinson's Disease (PD) and Multiple System Atrophy (MSA).
PATIENTS AND METHODS: 20 patients with PD and 13 patients with MSA were studied. 
After 12 hours in off medication, NE and GH were measured in supine position and 
NE after 5 minutes standing. Later, GH levels were recorded at 15, 30, 45 and 60 
minutes after a dose of 0.005 mg/kg of apomorphine. Finally, analysis of the 
symptoms of autonomic dysfunction and levodopa test were carried out.
RESULTS: Sympathetic response to postural changes was significantly higher in 
patients with PD (NE increase in relation to basal: PD: 170.90 +/- 110.08 pg/ml; 
MSA: 91.33 +/- 73.79 pg/ml; p = 0.029). No differences were found in the 
response of GH to apomorphine (GH peak at 45 minutes: PD: 2.37 +/- 2.7 ng/ml; 
MSA: 1.69 +/- 1.90 ng/ml; ns). The symptoms of autonomic dysfunction were more 
frequently in patients with MSA. The stridor was specific to MSA. Improvement in 
motor scores in the levodopa test was higher in patients with PD (PD: 39.7 %; 
MSA: 17.89; p = 0.019).
DISCUSSION: Sympathetic response to postural changes, description of symptoms of 
autonomic dysfunction, and motor response to levodopa test are useful tools in 
order to improve specificity of the diagnostic criteria of PD and MSA. The GH 
test with apomorphine was not useful for a differential diagnosis.