Definition and Overview
Sympathetic skin response (SSR) is an autonomic nerve function test that measures changes in skin electrical resistance that occur when sympathetic nerve activity in skin sweat glands changes due to various stimuli such as electrical stimulation, deep breathing, and sudden auditory stimulation.
SSR reflects the function of the sympathetic cholinergic pathway that innervates the eccrine sweat glands in the skin. A normal response occurs only when the efferent pathway from the brainstem through the lateral horn of the spinal cord to the postganglionic sympathetic fibers is intact.
Principle and measurement method
Inspection principle
When stimulation is given, sympathetic nerve activity in the skin sweat glands increases, which changes the electrical conductivity of the skin surface. This change in potential is recorded with a surface electrode.
stimulation method
- Electrical stimulation: Apply single-shot electrical stimulation (0.1 to 1 ms, 10 to 30 mA) to the wrist or ankle.
- Deep breathing stimulation: deep inspiration or Valsalva maneuver
- Auditory stimulus: sudden loud sound
Recording method
Recording is performed by attaching the active electrode to the palm or sole of the foot, and the reference electrode to the back of the hand or the top of the foot. After stimulation, potential changes are observed after a latency of about 1.5 to 3 seconds.
evaluation indicators
- Latency: Time from stimulus to onset of response.
- Amplitude: Magnitude of change in potential
- Waveform type: single phase or complex waveform
- Presence or absence of reaction: absent or present
Clinical significance
Diabetic autonomic neuropathy
In patients with diabetic autonomic neuropathy, SSR abnormalities (disappearance or prolonged latency) are observed in approximately 72-87% of patients. SSR is useful for early detection because abnormalities may appear before clinical symptoms.
Small Fiber Neuropathy
SSR evaluates the sympathetic pathway via unmyelinated C fibers and small diameter Aδ fibers. Even if the nerve conduction test is normal, SSR abnormalities may appear, so it is used as an auxiliary tool in diagnosing small fiber neuropathy.
Parkinson's Spectrum Disorders
SSR abnormalities are reported in Parkinson's disease, multiple system atrophy (MSA), and pure autonomic failure (PAF). The loss of SSR in MSA and PAF is more pronounced than in Parkinson's disease, which serves as a reference for differential diagnosis.
Anhidrosis
It is used to evaluate the cause of local or generalized anhidrosis. Loss of SSR in the area suggests damage to peripheral sympathetic nerve fibers.
diagnosis
normal standard
- Palm: Latency 1.5-2.5 seconds, based on upper extremity stimulation.
- Soles: Incubation period 2.0-3.0 seconds
- A normal baseline value according to age is needed, and the incubation period increases with age.
abnormal findings
Criteria for an abnormal SSR: - Absent response - Prolonged incubation period (exceeding normal standards) - Significant reduction in amplitude (criteria vary between studies)
Limitations of the test
SSR is influenced by various factors such as habituation by repeated stimulation, skin temperature, arousal state, anxiety, and drugs (anticholinergics, etc.). There is variation between examiners due to the absence of standardized testing protocols and normal reference values. For this reason, it is recommended to interpret it in conjunction with other autonomic nerve tests rather than as a standalone test.
treatment
Because SSR is a diagnostic test, there is no direct treatment. If SSR abnormalities are confirmed, treatment for the causative disease (diabetic autonomic neuropathy, small fiber neuropathy, Parkinson's spectrum disease) is given priority.
In diabetic autonomic neuropathy, improving blood sugar control is important to preserve autonomic function, and in small fiber neuropathy, customized treatment depending on the cause is necessary.
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This information is provided for medical educational purposes and is not a substitute for individual medical care or treatment. If you have any symptoms, be sure to seek professional advice. Inquiries: Osang Neurosurgery 1599-5453 | osns.co.kr