SSEP - Median and Posterior Tibial

UE (median) and LE (tibial) · Absolute latencies · Interpeak intervals · Side-to-side difference

Median Nerve - Upper Limbs

N4 · N9 · N13 · P14 · N18 · N20

Absolute latencies (ms)

Parameter Side R Side L Diff. R–L Limit Result

Interpeak Intervals

Interval Side R Side L Diff. Limit Result

Amplitudes (µV)

Parameter Side R Side L Diff. % Limit Result

Posterior Tibial - Lower Limbs

NP · N22 · P31/P34 · P40/P37

Absolute latencies (ms)

Parameter Side R Side L Diff. R–L Limit Result

Interpeak Intervals

Interval Side R Side L Diff. Limit Result

Amplitudes (µV)

Parameter Side R Side L Diff. % Limit Result

SSEP for other nerves

Dedicated calculators with nerve-specific references:

What are SSEP latencies and how to interpret them

SSEP measures absolute latencies and interpeak intervals (N9–N13, N13–N20 for median; P40–N22 for tibial). Compare to normative data and interside asymmetry.

This SSEP (somatosensory evoked potential) calculator accepts absolute latencies from the study (N9, N13, P14, N20, N22, P40, etc.), automatically compares each parameter with the selected reference norms, and calculates interpeak intervals and side-to-side difference.

Available references

  • Chiappa KH - Evoked Potentials in Clinical Medicine, 3rd ed. Lippincott-Raven, 1997. Values from 200+ healthy controls, widely used in North American labs.
  • DeLisa JA - Manual of Nerve Conduction Velocity and Clinical Neurophysiology. Raven Press. Classic reference with median and tibial values.
  • Maguière F - In: Electroencephalography and Clinical Neurophysiology Supplement. French-school values emphasizing absolute limits (mean + 2.5–3 SD).
  • Hussain AM - Reference with well-established side-to-side difference values, especially useful for asymmetric assessment.
  • Manguini M - Reference with absolute limits based on Brazilian/Latin American population, aligned with Brazilian Clinical Neurophysiology Society (SBNC) protocols.
  • Azar IA - Norms emphasizing absolute side-to-side differences for median latencies; varied height ranges for tibial.
  • EPM - Escola Paulista de Medicina / UNIFESP. X + 3 SD values for median and tibial SSEP, including P14, N18, P31, and P34 components.
  • Markand ON - Somatosensory Evoked Potentials. In: Aminoff MJ (ed.). Electrodiagnosis in Clinical Neurology. Limits = mean + 3 SD (99% confidence).
  • Kimura J - Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice, 4th ed. Oxford University Press. Limits = mean + 2 SD (95% confidence).

Median nerve SSEP components

N9 - Brachial plexus (Erb point). Upper trunk activation.
N13 - Cervical dorsal horn (C5–C6). Presynaptic.
P14 - Medial lemniscus / lower brainstem. Postsynaptic.
N20 - Primary somatosensory cortex (area 3b). Cortical generator.

Posterior tibial nerve SSEP components

NP - Popliteal fossa. Peripheral tibial nerve.
N22 - Lumbar spinal equivalent (L3–S1). Analogue of N13.
P31/P34 - Brainstem / subcortical.
P40/P37 - Somatosensory cortex (lower limbs, vertex). Height-dependent.

Interpeak interval interpretation

  • N9–N13: cervical spinal conduction. Abnormal in cervical myelopathies, syringomyelia, and multiple sclerosis.
  • N13–N20 / P14–N20: thalamocortical conduction. Sensitive to medial lemniscus, thalamic, and thalamocortical tract lesions.
  • N9–N20: total peripheral + central conduction time in upper limbs.
  • N22–P40 / NP–P40: spinocortical conduction in lower limbs. Abnormal in thoracic myelopathies and posterior column lesions.

Clinical support tool. Results must be interpreted in full clinical context. Does not replace a clinical neurophysiology specialist report.

Frequently asked questions

Which median SSEP latencies are assessed?

Peripheral (N9), subcortical (N13) and cortical (N20) components plus interpeak intervals.

How to interpret posterior tibial SSEP?

Evaluate P40, N22, P40–N22 interval and asymmetry for central vs peripheral delay.

Clinical content: Dr. Wardislau Ferreira · Reviewed by Dr. Carina Massaro

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