Sudomotor dysfunction is one of the earliest detectable neurophysiologic abnormalities in distal small fiber neuropathy. Sudomotor is a simple 2 minute test used to evaluate postganglionic sympathetic cholinergic activation through measuring (axon-reflex mediated) galvanic sweat response. Sweat glands are stimulated via iontophoresis of a cholinergic agent and the sweat production is measured as an increase of humidity through a foot electrode.
The skin response to the electrical stimulation of a sudomotor test acts as an effective diagnostic tool to detect early complications of the autonomic nervous system. Sudomotor testing can detect localized pre & postganglionic lesions providing early diagnosis of diabetes and other microvascular & neuropathic dysfunction. The sudomotor test is also useful in monitoring disease progression or recovery from therapy.
The sudomotor test is done with the use of 2 feet electrodes as a stand alone test or in conjunction with ANS testing. Stimulation of sweat production is measured by the change in humidity for a period of 2 minutes.
The test will yield three main components:
- Microvascular Circulation
- C Fiber Nerve Density
- Peak Sweat
In normal individuals, the sweat output begins until it reaches the peak sweat (inflection point) and decreases slowly. Sweat response can be absent, decreased or increased. A longer latency of the sweat onset can be seen as well as a lack of recovery. Increased sweat production is often a sign of axonal excitability, seen in patients with the onset or existence of diabetic neuropathy, reflex sympathetic dystrophy and other small fiber neuropathies.