Definition and Overview
Neuropathic pain is defined by the International Association for the Study of Pain (IASP) as “pain directly caused by lesions or diseases of the somatosensory nervous system.” Unlike nociceptive pain caused by tissue damage, it is pathological pain caused by abnormalities in the pain transmission pathway itself.
Approximately 7-10% of the general population experiences neuropathic pain, and approximately 20-25% of chronic pain patients have neuropathic components. The frequency continues to rise due to aging and increased prevalence of diabetes.
cause
peripheral neuropathy pain
- Diabetic polyneuropathy: The most common cause, neuropathic pain occurs in approximately 20-30% of diabetic patients.
- Postherpetic neuralgia: Pain that persists for more than 3 months after shingles.
- Trigeminal neuralgia: Paroxysmal electric shock-like pain in the face
- Traumatic nerve injury: phantom limb pain after surgery or amputation
- Chemotherapy-induced neuropathy: Platinum-based, vinca alkaloids, etc.
central neuropathy pain
- Central post-stroke pain: Occurs in approximately 8-10% of stroke patients
- Pain after spinal cord injury: Approximately 40-50% of spinal cord injury patients
- Pain related to multiple sclerosis
Symptom characteristics
spontaneous pain
It is pain that appears continuously or intermittently without external stimulation. It is characterized by a burning sensation, aching pain, and shooting pain that feels like electricity.
evoked pain
- Allodynia: Pain from normally harmless stimuli (light touch, temperature changes)
- Hyperalgesia: Excessive pain response to mildly painful stimuli.
paresthesia
It is accompanied by abnormal sensations such as tingling, numbness, and the feeling of ants crawling (formication). Neuropathic pain is characterized by a ‘paradoxical combination of positive and negative symptoms’ in which decreased sensation and pain coexist in the painful area.
diagnosis
Clinical diagnostic criteria
The following are evaluated according to the neuropathic pain diagnosis grading system revised in 2008:
1. Check whether the distribution of pain is in a neuroanatomically appropriate area. 2. Check to see if there is any history suggestive of a lesion or disease of the relevant nerve. 3. Physical examination confirms whether the sensory abnormality exists in a neuroanatomically corresponding area. 4. A test is performed to objectively confirm nerve lesions.
secondary inspection
- Nerve conduction test/electromyography: Objective confirmation of peripheral nerve damage
- Quantitative Sensory Testing (QST): Quantitative assessment of pain threshold and sensory function.
- Skin biopsy: Measures nerve fiber density within the epidermis and diagnoses small fiber neuropathy.
- MRI: Check for central nervous system lesions (stroke, spinal cord lesions)
screening tool
Screening tools such as the DN4 (Douleur Neuropathique 4) questionnaire, painDETECT, and LANSS (Leeds Assessment of Neuropathic Symptoms and Signs) are used in clinical practice.
treatment
Primary drug treatment
The first-line treatments recommended by international guidelines are as follows.
- Gabapentinoids: gabapentin (1,200 to 3,600 mg per day), pregabalin (150 to 600 mg per day). The number needed to treat (NNT) is approximately 7.7.
- SNRI: duloxetine (60-120 mg daily). NNT is about 6.4.
- Tricyclic antidepressants: amitriptyline (25 to 150 mg daily). It has the lowest NNT of approximately 3.6, but the side effect profile must be considered.
Secondary and adjuvant treatment
- Topical treatment: Capsaicin 8% patch, Lidocaine 5% patch (focal neuropathic pain)
- Tramadol: Short-term use for moderate pain.
- Combination therapy: When a single drug is not effective enough, drugs with different mechanisms are used together.
Non-drug treatment
- Transcutaneous electrical nerve stimulation (TENS): adjuvant effect on peripheral neuropathic pain
- Transcranial Magnetic Stimulation (rTMS): Repetitive primary motor cortex stimulation is effective for central pain.
- Spinal Cord Stimulation (SCS): Significant pain reduction in 50-70% of patients with drug-refractory pain
- Cognitive Behavioral Therapy (CBT): Management of pain-related psychological factors, recovery of function
Progress and prognosis
Neuropathic pain has a strong tendency to become chronic, and it is often difficult to expect complete pain relief with a single treatment. A systematic review found that even with first-line treatment, pain reduction of more than 30% was achieved in only about 50% of patients. However, it is possible to reduce pain intensity, improve function, and improve quality of life through a multidisciplinary approach (drug + non-drug + psychological intervention).
Early diagnosis and initiation of active treatment are important to inhibit the progression of central sensitization and prevent chronicity.