Chronic autonomic failure: CSF and plasma 3-methoxy-4-hydroxyphenylglycol.

We measured CSF and plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) in patients with orthostatic hypotension. Total CSF MHPG levels were significantly lower than normal in patients with either multiple system atrophy (MSA) or idiopathic orthostatic hypotension (IOH). Only IOH patients had low plasma levels of MHPG. Correction of CSF MHPG levels for the contribution from plasma free MHPG provides an index of central norepinephrine metabolism. In MSA, abnormal function of central noradrenergic pathways seems to cause the low CSF MHPG levels. In IOH, the decreased CSF MHPG results from the diminished plasma MHPG levels.