Autonomic Failure Tests

Autonomic Failure Tests

05 November 2004

Other Noninvasive Tests

Heart rate variability:	power spectral analysis
	QT interval
	24 hour monitoring

Sweat tests:	thermoregulatory sweat test
	QSART
	Alizarin

Plasma noradrenaline levels

Pupillary function	4% cocaine: absent with lesion anywhere in oculosympathetic path
	6-hydroxyamphet: dilate when postganglionic fibres intact
	0.1% adrenaline: no effect on normal BUT dilate from denervation hypersensitivity when postganglionic affected
	2.5% methacholine: mioisis when impaired parasym innervation
	0.125% pilocarpine: mioisis when impaired parasym innervation

Invasive Tests

1. confirmation when equivocal noninvasive results

2. localization

3. research

abnormalities >/= 2 noninvasive tests correlate well with abnormalities in intra-arterial Valsalva responses.

Intraneural recordings for postganglionic sympathetic activity

Infusion of pressor drugs

Axon reflex via intradermal Ach: sweating & piloerection if postgang symp intact

Diseases affecting CNS

MSA:

sporadic, progressive, adult onset disorder

Autonomic dysfunction

Parkinsonism

Ataxia

Variants:	Shy Drager
	Striatonigral degeneration
	OPCA

Path: preganglionic neurons

Abnormal HR response

Abnormal sweat test inc QSART

Normal supine plasma free noradrenaline but no rise in tilt

Reduced standing plasma free noradrenaline

Reduced dopamine-b-hydoxylase

Pure autonomic failure:

sporadic, progressive, adult onset

Mainly orthostatic hypotension

Frequently bladder & sweating impairment

Path: sympathetic ganglia & post synaptic neurons

Abnormal HR response

Abnormal sweat test inc QSART

Reduced supine plasma free noradrenaline but no rise in tilt

Reduced standing plasma free noradrenaline

Reduced dopamine-b-hydoxylase

Parkinson:

rare postural hypotension

HR response maybe mildly impaired

Orthostatic hypertension:

congenital deficiency of dopamine b hydroxylase

Pure symp failure with absent nor release

Normal cholinergic ie sweating

References

McLeod JG, Tuck RR Disorders of the Autonomic Nervous System: Part 1. Pathophysiology and Clinical Features. Annals of Neurology 21: 419 – 427, 1987.

McLeod JG, Tuck RR Disorders of the Autonomic Nervous System: Part 2. Investigation and Treatment. Annals of Neurology 21: 519 – 527, 1987.