Uses of Somatosensory Evoked Potentials (SSEPs) in Peripheral Neuropathy Evaluation
SSEPs should be reserved as a second-line diagnostic test in peripheral neuropathy evaluation, used only when standard electroneuromyography (ENMG) is inconclusive or when assessing proximal/inaccessible nerve segments that cannot be adequately evaluated by conventional nerve conduction studies. 1
Primary Clinical Applications
When SSEPs Add Diagnostic Value
Proximal nerve segment assessment: SSEPs are most useful for evaluating conduction along inaccessible proximal segments of limb nerves where conventional nerve conduction studies cannot reach 2, 3
Absent peripheral responses: When sensory nerve action potentials (SNAPs) are absent or severely attenuated (≤1 microV) but motor responses remain recordable, SSEPs can provide information about residual sensory conduction through central amplification 4
Brachial plexopathies: SSEPs help localize lesions within the plexus, though they may only demonstrate the most distal lesion when multiple lesions are present 2, 3
Guillain-Barré syndrome: SSEPs may evaluate proximal conduction abnormalities, though their definitive value remains unclear since pathology is often predominantly proximal 2
Technical Approach and Integration with ENMG
Complementary Information Provided
Central and proximal peripheral conduction: SSEPs provide valuable complementary data on somatosensory pathway conduction that ENMG cannot assess 1
Sensory-motor comparison: In demyelinating neuropathies, SSEPs allow comparison of afferent (sensory) versus efferent (motor) conduction velocities by calculating the difference in response latency between proximal and distal stimulation sites 4
Critical Limitations and Pitfalls
When SSEPs Provide Misleading Information
Multiple lesion scenarios: SSEPs demonstrate only the electrophysiologic consequences of the most distal lesion present, potentially masking more proximal pathology 2
Falsely normal results: SSEPs can show normal conduction velocity despite significant peripheral neuropathy because central amplification may magnify responses from a few normally-conducting axons, masking the dysfunction of the majority 4
Radiculopathies: SSEPs to nerve trunk stimulation are generally not helpful in isolated radiculopathies; dermatomal or cutaneous nerve stimulation has provided conflicting results 2
Conduction velocity calculations: In peripheral neuropathies, SSEPs sometimes provide misleading information about actual conduction velocity and should not be the sole basis for velocity determination 2
Specific Contraindications to Relying on SSEPs
Do not use SSEPs as the primary test to determine organic versus nonorganic sensory loss, though they may be one factor in this determination 2
Do not rely on SSEPs alone when ENMG can provide direct peripheral nerve assessment 1
Recommended Clinical Algorithm
Step 1: Perform Standard ENMG First
- Complete nerve conduction studies and needle EMG remain the first-line evaluation 1
Step 2: Consider SSEPs When:
- SNAPs are absent but clinical suspicion for residual sensory function exists 4
- Proximal nerve segments (plexus, nerve roots) require assessment beyond ENMG capability 2, 3
- ENMG findings are inconclusive or discordant with clinical presentation 1
Step 3: Interpret SSEPs Cautiously
- Always integrate SSEP findings with ENMG data rather than interpreting in isolation 5, 1
- Recognize that normal SSEPs do not exclude significant peripheral neuropathy 4
- Consider that abnormal SSEPs may reflect only the most distal pathology 2
Practical Recording Considerations
- Standardized protocols should include measurement of multiple parameters along the somatosensory pathway 1
- Mixed or purely sensory nerve stimulation provides reliable measurement of peripheral and central sensory conduction 5
- Comparison with motor conduction helps identify disproportionate sensory versus motor involvement in demyelinating conditions 4