Factor Iii Sudomotor Changes And Edema

Differential sweating between the affected and unaffected side is regarded as one of the diagnostic criteria for CRPS.26 Sweat production is a sympathetic cholinergic function, and variations occur in response to a wide variety of stimuli. Physiological variations are typically symmetric, and usually involve both hands and feet, as well as the head and trunk. These changes can occur apparently spontaneously or be induced by external or internal factors. These may include environmental temperature, physical activity, or psychological stress. If there is reduced sympathetic efferent activity in CRPS or other conditions, the affected extremity is likely to be warm and dry compared to the unaffected side. However, increased sympathetic efferent activity is likely to be associated with a cold, sweaty extremity compared to the unaffected side.

Measurement of sudomotor activity is difficult and not generally available. The quantitative sudomotor axon reflex test (QSART) is a validated test for CRPS. It measures resting sweat output and response to iontophoretically applied acetyl choline, comparing the affected and unaffected sides.

The thermoregulatory sweat test gives most information in small fiber neuropathy and autonomic failure, and has not been rigorously evaluated in CRPS. It is complicated and expensive, and not generally performed, even in tertiary centers. Some insurance companies restrict the use of such tests (Table 27.3).

Sympathetic skin responses may be of some value in the diagnosis of CRPS, if asymmetric.27 The clinical observation that one hand or foot appears moist may be the only objective evidence of this factor. This change might only be present on occasions of physical or emotional stress, or may accompany a severe episode of pain.

Peripheral edema is a common clinical finding in many conditions. However, it is unilateral, localized edema that is of diagnostic significance in CRPS. This is not like the dependent, pitting ankle edema of congestive cardiac failure or the brawny lymphedema of the arm after axillary node dissection. This localized edema has been described by several authors (reviewed in Ref. 26), and is possibly neurogenic in origin.28

Edema is often not measured at all, but the patient may comment that there is too much swelling to wear customary rings or the veins cannot be seen. Quantitative measures, such as volume displacement of the hand or foot, or finger diameter, are rarely recorded. Patients and clinicians often note, however, that the sweating and edema resolve when the CRPS resolves. They could theoretically be used to monitor severity and progress. There are therefore no specific treatments that can be directed at these factors.

There are no studies of interrater reliability or of the reliability of self-observation of either sweating or edema. Both are very difficult to measure and the framers of the

Table 27.3 Aetna Clinical Policy Bulletin: autonomic testing/sudomotor tests. Test

I Aetna considers autonomic testing such as quantitative sudomotor axon reflex test A Diabetic autonomic neuropathy;

(QSART), thermoregulatory sweat test (TST), and silastic sweat imprint medically or necessary for use as a diagnostic tool for any of the following conditions/disorders: B Amyloid neuropathy; or

C Sjogren's syndrome; or D Idiopathic neuropathy; or E Pure autonomic failure; or F Multiple system atrophy; or G Distal small fiber neuropathy; or H Reflex sympathetic dystrophy or causalgia (sympathetically maintained pain)

Aetna considers autonomic testing experimental and investigational for all other indications

II Aetna considers sympathetic skin response testing experimental and investigational for any indications because it has a relatively low sensitivity and uncertain specificity, and the peer-reviewed medical literature does not support its effectiveness

www.aetna.com/cpb/medical/data/400_499/0485.html.

factors were well aware of this dilemma. The criteria require that these changes be observed at some time during the course of the condition, but prospective studies are lacking.

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