Sympathetic neural outflow directly recorded in patients with primary autonomic failure: clinical observations, microneurography, and histopathology.

We evaluated 2 patients with primary autonomic failure, without clinical peripheral neuropathy. One had primary autonomic failure alone (PAF), and the other had autonomic failure and multiple system atrophy (MSA). Direct intraneural recordings demonstrated a marked reduction of sympathetic efferent nerve impulse activity in the PAF patient. The patient with MSA had spontaneous bursts of sympathetic nerve impulses that confirmed the functional integrity of post-ganglionic sympathetic efferent neurons. Neurosecretory activity of these neurons correlated with the electrophysiologic findings. The PAF patient had markedly reduced supine norepinephrine (NE) levels that did not rise upon standing. The supine NE level in the MSA patient was normal. Morphometric study of biopsied sural nerve in the MSA patient showed that unmyelinated fibers were normal, whereas the nerve of the PAF patient showed clear evidence of past degeneration. We suggest that the primary preganglionic sympathetic defect in MSA releases viable postganglionic sympathetic efferents from central control. Decentralized postganglionic elements may fire spontaneously, thus activating peripheral effectors and providing potentially useful signs and symptoms for differential diagnosis.