The comparison of clonidine, arginine and both combined: a growth hormone stimulation test to differentiate multiple system atrophy from idiopathic Parkinson's disease.

This study was aimed at comparing the diagnostic accuracy of the growth hormone (GH) response to clonidine, arginine and both combined in order to establish a more reliable test to differentiate parkinsonism type multiple system atrophy (MSA-p) from Parkinson's disease (PD). Twenty-four patients with MSA-p and 26 cases with PD entered the study. They were submitted to treatments of clonidine, arginine and a combination of the two in a random manner on three different nonconsecutive days. The GH peak in serum at different times was evaluated and used as a primary variable for analysis of the stimulation test. By ROC analysis, we compared the sensitivity and specificity of tests of clonidine, arginine and both combined. After clonidine administration, the maximal average was significantly lower in patients with MSA-p than in those with PD (3.62 +/- 0.81 vs. 6.91 +/- 1.13; P < 0.05) with a sensitivity and specificity of 82.61 and 76.92%. After arginine administration, the maximal average GH concentration in serum at 30 min was also significantly lower in patients with MSA-p than in those with PD (4.07 +/- 0.80 vs. 7.89 +/- 1.29; P < 0.05) with a sensitivity and specificity of 78.26 and 73.08%. The sensitivity and specificity in differentiating MSA-p from PD was higher in the clonidine GH stimulation test than in the arginine GH stimulation test. However, when the clonidine and arginine were applied combined, the contrast of the maximal average GH concentration in serum in two groups was markedly increased (5.02 +/- 1.12 vs. 10.75 +/- 1.11; P < 0.05) with a sensitivity and specificity of 73.91 and 92.31%, and the specificity was notably increased in the combined GH stimulation test. Compared to the arginine GH stimulation test, the clonidine GH stimulation displayed a higher sensitivity and specificity; combined GH stimulation test of clonidine plus arginine could significantly enhance the specificity in differential diagnosis of MSA-p from PD.