Neuropathic Pain Below Level of Injury: Sensory Mapping and TENS
In short
Clinical assessment of central neuropathic pain below the injury level. Sensory mapping, allodynia, transcutaneous electrical nerve stimulation (TENS), and gabapentin synergy.
In this guide (3 sections)
Chronic pain affects up to 80 percent of individuals living with spinal cord injury, with central neuropathic pain below the level of injury representing the most severe, intractable, and psychologically devastating form. Unlike nociceptive musculoskeletal pain resulting from joint overuse or muscle spasm, central neuropathic pain is generated directly by injury to the somatosensory tracts within the spinal cord. Patients describe this pain as continuous burning, stabbing, freezing, crushing, or electric-shock sensations in body regions that are otherwise completely paralyzed and devoid of normal touch sensation.
Classification and Mechanisms of Central Below-Level Neuropathic Pain
The pathophysiology of below-level neuropathic pain involves complex maladaptive neuroplasticity within the central nervous system. Mechanical disruption of the spinothalamic tracts leads to deafferentation of third-order sensory neurons in the thalamus and secondary neurons within the dorsal horn. This deafferentation induces spontaneous neuronal hyperactivity, loss of GABAergic inhibitory interneurons, microglial activation, and NMDA receptor upregulation. These hyperactive central sensory circuits generate spontaneous pain perceptions and amplify tactile inputs, producing severe hyperalgesia (exaggerated pain response to mildly painful stimuli) and allodynia (pain provoked by innocuous stimuli like clothing brushing the skin).
| Pain Classification | Anatomical Location | Pain Descriptors & Quality | Optimal Management Approaches | |
|---|---|---|---|---|
| Central Below-Level Neuropathic Pain | Diffuse areas below the neurological level of injury, including paralyzed limbs. | Constant burning, electric shocks, freezing cold, crushing, severe allodynia. | Gabapentinoids (pregabalin, gabapentin), SNRIs, TENS at/above lesion, visual feedback. | |
| At-Level Neuropathic Pain | Segmental band-like distribution within 2 dermatomes of the neurological level. | Sharp, lancinating, shooting pain, radicular distribution, localized hypersensitivity. | Nerve root decompression, topical lidocaine patches, tricyclic antidepressants. | |
| Musculoskeletal Nociceptive Pain | Shoulder girdle, neck, wrist, and non-paralyzed axial paraspinal joints. | Dull, aching, throbbing, mechanically aggravated by movement and wheelchair propulsion. | Physiotherapy, ergonomic modification, NSAIDs, rotator cuff strengthening. |
Standardized Sensory Mapping and Assessment Protocols
Accurate charting using a standardized body map differentiates central neuropathic pain from musculoskeletal pain. Quantify pain intensity using the Numeric Pain Rating Scale (NPRS) and characterize sensory features using the Neuropathic Pain Symptom Inventory (NPSI) or Douleur Neuropathique 4 (DN4) tool.
Standardized High-Frequency TENS Application Protocol
Objective: Activate large-diameter A-beta sensory afferents above the level of injury to modulate dorsal horn excitability via the gate control mechanism.
- 1Cleanse the intact skin over the chosen electrode placement site above or at the margin of the neurological level of injury.
- 2Place two pairs of self-adhesive electrodes along the dermatomal distribution corresponding to intact sensation rostral to the lesion.
- 3Set the TENS unit to conventional high-frequency mode (frequency 80 to 100 Hz, pulse width 50 to 100 microseconds).
- 4Gradually increase electrical amplitude until the patient reports a strong, comfortable tingling sensation without muscle twitching or pain.
- 5Maintain continuous stimulation for 30 to 45 minutes while the patient rests in a quiet, supported posture.
Domestic Indian Patient Education and Coping Strategies
In Indian society, chronic pain in paralyzed limbs is frequently misunderstood by family members, who may assume that because the patient cannot move the legs, they cannot possibly feel real physical pain. This often leads to skepticism or accusations of psychological exaggeration. Physiotherapists must educate families about phantom-like central neuropathic pain, explaining that the brain continues to receive false pain signals from damaged spinal pathways. Supportive family validation and mindfulness pacing substantially reduce pain-related suffering.
Synergistic Pharmacotherapy and Non-Pharmacological Modalities
Monotherapy is rarely sufficient for central neuropathic pain. Optimal clinical outcomes require a multimodal strategy combining neuromodulatory medications with non-pharmacological physical therapies.
- First-Line Gabapentinoids: Pregabalin (150 to 600 mg daily) or gabapentin binds the alpha-2-delta subunit of voltage-gated calcium channels, dampening neurotransmitter release.
- Serotonin-Noradrenaline Reuptake Inhibitors (SNRIs): Duloxetine (60 mg daily) augments descending inhibitory noradrenergic pathways, providing synergistic analgesia.
- Virtual Reality and Mirror Therapy: Visual feedback reflecting intact upper limb movement into lower limb virtual space reduces central maladaptive sensory reorganization.
Avoid long-term opioid analgesics for central neuropathic pain in spinal cord injury. Opioids exhibit low efficacy for central deafferentation pain, while causing severe gastrointestinal constipation, worsening neurogenic bowel, and suppressing respiratory drive.
Frequently Asked Questions
Why does a patient feel burning pain in legs that are completely paralyzed and numb to touch?
Central neuropathic pain originates from damaged, hyperactive pain pathways within the injured spinal cord and thalamus. Even though sensory inputs from the skin cannot reach the brain, the damaged central neurons fire spontaneously, which the brain interprets as real, burning pain in the legs.
Where should TENS electrodes be placed if the legs have zero sensation?
Electrodes must never be placed on anesthetic skin below the lesion, as this risks cutaneous burns and cannot transmit signals past the cord block. TENS electrodes must be applied over dermatomes with intact sensation at or just above the injury level to stimulate intact spinal inhibitory circuits.
Do patients in India need a doctor referral to begin specialized neuro-physiotherapy?
Under the National Commission for Allied and Healthcare Professions (NCAHP) Act 2021, registered physiotherapists are recognized as primary contact practitioners. You can consult a licensed neuro-physiotherapist directly without a physician prescription. At BookPhysio.in, every practitioner is verified, and you pay directly per session without hidden fees or platform markups.
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