Sudomotor symptoms are common, but do not usually command much attention. Initially, there may be hyperhidrosis of the feet associated with coldness (I can't keep my feet warm). This is followed by anhidrosis and vasomotor alterations, which can be variable, with venous congestion and a purple discoloration being common. Some patients will have alternating warming and cooling. Infrequently, widespread anhidro-sis results in heat intolerance. In these patients, a high ambient temperature and sustained physical exertion results in overheating. In most patients, the diabetic state results in a significant impairment in exercise capacity, and heat intolerance does not develop.
Gustatory sweating commonly occurs in diabetics with cervical sympathetic dener-vation. The patient has excessive facial sweating in response to food, especially spicy food. The suggested mechanism is denervation of postganglionic sudomotor fibers with faulty reinnervation, although some evidence suggests a more dynamic metabolic mechanism and an association with nephropathy.
Sudomotor deficits are very common if quantitative approaches are used to detect autonomic sudomotor impairment. It is important to detect the severity and distribution of sudomotor deficit. The most commonly used tests to evaluate sudomotor function are as follows:
1. Quantitative Sudomotor Axon Reflex Test (QSART).
2. Thermoregulatory sweat test.
3. Sympathetic skin response (SSR).
4. Skin biopsy.
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