Autonomic neuropathy

Regarding making the diagnosis of autonomic neuropathy, which one of the following

statements is CORRECT?

a) Anhydrosis is the most common presenting symptom

b) A normal sinus arrhythmia involves mild elevation of heart rate during expiration

and mild depression during inspiration

c) A Valsalva manoeuvre is of no use as a bedside test

d) During a sustained handgrip, a normal response would be an increase in diastolic

blood pressure of >16mmHg in the opposite arm

e) The patient’s ability to perform mental arithmetic may aid diagnosis at the bedside

Answer: d

Explanation

Autonomic neuropathy describes a central or peripheral lesion of the autonomic nervous

system, which results in dysfunction of its homeostatic function. Consequences for

anaesthesia should not be underestimated as dramatic hypotension may be seen at

induction of general anaesthesia or while establishing central neuraxial blockade. The

patient may be at increased risk of aspiration of gastric contents and anaesthesia, surgery

and recovery may provoke cardiac or respiratory arrest without prodrome. The causes

may be considered in terms of their anatomical level: central or peripheral nervous

system, primary or secondary. Diabetic and alcoholic neuropathies are two common

causes and Guillian–Barré syndrome and porphyria are other diagnoses that the anaesthetist

will remember; however, the list of described causes is extensive. The patient will

most commonly present with orthostatic hypotension and may develop hypohydrosis.

Bedside tests involve provoking the autonomic nervous system to respond to a predictable

stressor. Lying–standing blood pressure measurement may provoke a drop of over

30mmHg.Normal sinus arrhythmia (inspiration increases heart rate, expiration decreases

it) and normal Valsalva response may be sought. In healthy subjects an increase in blood

pressure will be seen caused by elevated sympathetic outflow associated with isometric

exercise (sustained hand grip over threeminutes), cold pressor test (immersion of hand in

ice-coldwater for 90 seconds) ormental arithmetic (serial 7 or 17 subtraction from a given

figure). With respect to Option (e), it is not the patient’s ability to perform mental

arithmetic that aids diagnosis,more their haemodynamic response to performing the task.

Reference

Arbogast SD, Miles JD. Autonomic neuropathy. eMedicine 25 June 2009. Online at

http://emedicine.medscape.com/article/1173756-overview (Accessed 30 October 2009)