Factor Ii Vasomotor Changes

CRPS typically has pathological changes in the regulation of skin blood flow that is observed by the patient and medical attendants.20 Vasodilatation and/or vasoconstriction occur, and are significant subjective and objective measures. The tone of the cutaneous vessels is maintained by both tonic and phasic activity in the sympathetic system in addition to antidromic vasodilatation. Changes in the blood flow of deeper structures, such as muscle and bone, are much more difficult to observe.21

Estimation of skin perfusion in real time may be obtained with laser Doppler flowmetry or by measurement of skin temperature. Simultaneous (or contemporaneous) measures must be obtained symmetrically from the unaffected extremity for four reasons.20

1. Cutaneous perfusion is usually symmetric.

2. Skin blood flow and temperature change in response to a variety of external and internal influences.

3. Laser Doppler measures relative flows.

4. Antidromic vasodilatation shows significant interindividual differences.

Vasomotor instability in acute CRPS may be related to changes in sympathetic tone, antidromic activity, as well as to neurogenic inflammation.22 These changes, in addition to central changes, are capable of producing "warm" CRPS, as well as "cold" CRPS.23 Evidence has suggested that cutaneous sympathetic vasoconstrictor tone may be reduced in the acute period, and skin blood flow may be increased. It is therefore not likely that sympathetic blockade will have any therapeutic effect during this phase.

Chronic CRPS has traditionally been regarded as cold. Sympathetic overactivity or supersensitivity to circulating catecholamines are the putative explanations for this phenomenon. Some studies indicate that the affected limb is always cooler than the contralateral side during whole-body heating (for example, during a thermoregulatory sweat test). Microneurography studies suggested that sympathetic efferent activity was reduced, and assays of circulating catechols showed reduced venous levels in the affected extremity. It is suggested that adrenergic super-sensitivity to circulating catechols might be the culprit.

There are, of course, other influences on vasomotor control. For example, endothelial-derived nitric oxide or prostacyclins might be involved in vasodilatation.

Diagnostic value of vasomotor disturbance in the diagnosis of CRPS has been difficult to evaluate.24 Dynamic changes in skin blood flow reduce the diagnostic value of skin temperature differences in CRPS. There are both short-term changes related to sympathetic control and long-term changes related to the underlying pathology and disuse.

Sensory symptoms Incidence (%)

It has been suggested that temperature asymmetry under stable baseline conditions (20 minutes at rest with environmental temperature of 20°C) can be used. A difference of 0.6°C (infrared thermometry) discriminated between CRPS and other conditions with a sensitivity of 68 percent and specificity of 67 percent. More complex measurements, for example with computerized thermo-graphy, have not entirely clarified the problem.25

Other pathologies also cause differences in skin temperatures of the affected and unaffected extremities. Acute arthritides, inflammatory disorders, vascular disorders, and peripheral neuropathies are all capable of producing significant temperature asymmetries.

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