Can catecholamine measurements localize the site of autonomic dysfunction?
Patients with a neuropathy causing a primarily postganglionic autonomic abnormality (such as pure autonomic failure) have a subnormal plasma level of norepinephrine in the supine position that fails to increase during standing.
In patients with intact postganglionic neurons (such as multiple system atrophy) the plasma level of norepinephrine in the supine position remains within normal limits but fails to increase upon standing, similar to postganglionic abnormalities.
Because of considerable overlap between preganglionic and postganglionic abnormalities in individual patients with autonomic dysfunction, plasma norepinephrine values alone are usually not sufficiently diagnostic for the site of the lesion.
