Neuropathic pain
Neuropathic pain or neuralgia is pain which occurs due to injury or disorder of the somatosensory nervous system, either peripherally or sentrally. This is in contrast to nociceptive pain, which is pain due to noxious stimulation of pain receptors.
It’s usually chronic and debilitating, and unfortunately relatively prevalent (3 – 10% of population).
Etiology
- Peripheral causes
- Polyneuropathy (like diabetes, cytostatic, vasculitis)
- Entrapment syndromes (like carpal tunnel)
- Post surgery (like phantom pain)
- Herpes zoster and postherpetic neuralgia
- Radiation
- Central causes
- Stroke, especially brainstem/thalamus
- Tramatic brain/spinal cord injury
- Multiple sclerosis
Clinical features
Neuropathic pain can be continous or intermittent and paroxysmal, and usually has a burning or electrical shock-like characteristic. Other features include:
- Hypoestesia – decreased sensibility to non-painful stimuli
- Hypoalgaesia – decreased sensibility to painful stimuli
- Paraesthesia – abnormal “pins and needles” sensation
- Allodynia – pain upon non-painful stimuli
- Hyperalgaesia – severe pain upon mild painful stimuli
Diagnosis and evaluation
The diagnosis of neuropathic pain is clinical. Screening questionnaires like DN4, PainDETECT and LANSS can be used to distinguish neuropathic pain from other types.
Following the diagnosis, appropriate neurological examination and investigations must be performed to determine the etiology.
Treatment
Unfortunately, most patients can’t achieve a pain-free state, and it’s important to communicate this to the patient to not set their expectations too high. The evidence is not strong for non-pharmacological interventions like CBT, transcutaneous nerve stimulation, or physiotherapy, but it’s quite strong for pharmacological therapy.
The following are first choice drugs in the management of neuropathic pain:
- Gabapentin and pregabalin
- Tricyclic antidepressant
- Duloxetine and venlafaxine
- Carbamazepine and oxcarbazepine (mostly used for trigeminal neuralgia)
- Lidocaine patch
- Capsaicin patch
Opioids and botulinum toxin only have weak evidence of effect and are therefore second line drugs. Cannabinoids don’t have much evidence of effect but they have a good safety profile. Paracetamol and NSAIDs aren't very efficacious.