Somatosensory Evoked Potentials (SSEPs)
Somatosensory Evoked Potentials (SSEPs)
SSEPs are neurophysiological tests that assess the functional integrity of somatosensory pathways from peripheral nerves through the dorsal column-medial lemniscal system to the somatosensory cortex.
Key Points
- Non-invasive assessment of sensory pathway function
- Evaluates large-fiber sensory pathways
- Useful in both diagnostic and monitoring applications
- Can be performed in unconscious patients
- Provides objective neurological assessment
Stimulation Parameters
- Stimulus Characteristics
- Electrical pulses: 0.1-0.3 ms duration
- Intensity: motor threshold + 2-3 mA
- Rate: 2-5 Hz for diagnostic studies
- Common stimulation sites:
- Upper limb: median nerve at wrist
- Lower limb: posterior tibial nerve at ankle
- Recording Setup
- Upper Limb Recording Points
- Erb's point (peripheral plexus)
- C7 (cervical spine)
- C3'/C4' (cortical)
- Lower Limb Recording Points
- Popliteal fossa
- L1 (lumbar)
- Cz' (cortical)
- Upper Limb Recording Points
Recording Parameters
- Filter settings: 30-3000 Hz
- Analysis time: 50-100 ms
- Minimum 500-1000 averages
- At least two replications
Upper Limb SSEP Components
- N9 (Erb's point)
- Brachial plexus potential
- Latency: ~9-11 ms
- Peripheral nervous system marker
- N13 (Cervical)
- Cervical cord gray matter
- Latency: ~13-15 ms
- Spinal cord function indicator
- N20 (Cortical)
- Primary somatosensory cortex
- Latency: ~20 ms
- Key cortical response
Lower Limb SSEP Components
- N8 (Popliteal)
- Peripheral nerve potential
- Latency: ~8 ms
- N22 (Lumbar)
- Lumbar cord gray matter
- Latency: ~22 ms
- P37 (Cortical)
- Primary somatosensory cortex
- Latency: ~37 ms
Diagnostic Applications
- Central Nervous System
- Multiple sclerosis
- Spinal cord compression
- Myelopathy assessment
- Brain injury evaluation
- Peripheral Nervous System
- Brachial plexopathy
- Peripheral neuropathy
- Radiculopathy
- Intraoperative Monitoring
- Spine surgery
- Brain surgery
- Vascular procedures
- Real-time pathway assessment
Prognostic Applications
- Coma assessment
- Hypoxic-ischemic injury
- Spinal cord injury
- Post-operative recovery prediction
Age-Related Factors
- Neonates and Infants
- Longer latencies due to incomplete myelination
- Modified normative values needed
- Developmental changes monitoring
- Special electrode sizing
- Technical Adaptations
- Reduced stimulus intensities
- Shorter inter-stimulus intervals
- Modified electrode placement
- Age-specific protocols
Specific Pediatric Applications
- Developmental Assessment
- Myelination monitoring
- Neurological maturation
- Birth injury evaluation
- Disease Monitoring
- Hereditary disorders
- Metabolic diseases
- Neurodegenerative conditions
Normal Parameters
- Latency Measurements
- Absolute latencies
- Interpeak latencies
- Side-to-side differences
- Amplitude Analysis
- Peak-to-peak measurements
- Side-to-side comparisons
- Wave form morphology
Abnormal Patterns
- Central Conduction Defects
- Prolonged central conduction time
- Absent cortical responses
- Abnormal wave morphology
- Peripheral Pathology
- Delayed peripheral latencies
- Normal central conduction
- Reduced amplitudes
- Mixed Pathology
- Combined abnormalities
- Complex wave alterations
- Multiple component involvement
