The Aword

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Applications in Pain Evaluation

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Autonomic testing is safe and reliable. No specific pattern is associated with chronic pain per se.

ANS testing is valuable in assessment of CRPS I and sympathetically maintained pain. In patients with burning feet, autonomic tests have demonstrated subtle abnormalities even when clinical examination and nerve conduction studies are normal.

When studying patients with postural tachycardia syndrome, a higher than expected incidence of migraine sufferers has been noted;  further study revealed subtle adrenergic abnormalities suggesting vasomotor instability.

Other pain conditions have been associated with reduced orthostatic tolerance, such as chronic fatigue syndrome. Anecdotal reports of abnormal autonomic testing in fibromyalgia have appeared; these data need confirmation.




1.      scintigraphic triphasic bone scanning (SBS) : but some studies have found this test abnormal in no more than 25-55% of CRPS cases.

2.      Infrared thermal imaging (ITI) : can identify areas of damage which show increased temperature; areas of irritation, that show reduced temperature. The function of skin temperature is the domain of the sympathetic nervous system. Cold-stress ITI may be helpful.

3.      CT/MRI scans: not sensitive enough to detect microscopic nerve damage (note: only 5% of nerve fibres need to be disrupted in order to cause severe pain).

4.      EMG/NCV nerve conduction studies: not useful because they detect abnormalities in myelinated nerves; CRPS involves poorly myelinated/unmyelinated nerves.

5.      QSART studies (see above) : looks at parasympathetic more than sympathetic

6.      Diagnostic nerve blocks: (NOTE: invasive so not recommended by the Trust) are positive in the early stages but gradually lose their sensitivity.

7.      Laser doppler flow: a sensitive test to study small blood vessel (capillary) circulation. It has demonstrated that sympathectomy is ineffective in providing increased circulation to the extremity.