Neuropathic pain (nerve pain)

• What is neuropathic pain?
• Statistics
• Risk factors
• Progression
• Symptoms
• Clinical examination
• How is it diagnosed?
• Prognosis
• Treatment
• References

What is neuropathic pain?

Neuropathic pain is defined as pain caused by a lesion or dysfunction in the nervous system. There is no noxious (pain causing) stimulus that is causing the pain. Rather, the pain results from inappropriate signals in the nervous system. Unlike physiologic pain, which serves to warn and protect individuals from possible or actual injury, neuropathic pain serves no useful purpose.
Some examples of peripheral neuropathic pain include:

• Postherpetic neuralgia (pain occurring after shingles);
• Diabetic neuropathy;
• Pain following limb amputation.

Some causes of central neuropathic pain include:

• Pain following stroke;
• Pain following spinal cord injury.

Statistics of neuropathic pain

As many as one in five Australians suffer from chronic pain. Many of these patients will have an element of neuropathic pain contributing to their overall pain syndrome. For example, more than half of all patients suffering from chronic low back pain have a significant neuropathic component to their pain.

Risk factors of neuropathic pain

Predisposing factors for the development of neuropathic pain are dependent on the underlying cause of the pain.
For example, predisposing factors for the development of post-herpetic neuralgia include development of shingles on the face; and diabetes mellitus is a predisposing factor for the development of diabetic neuropathy.

Progression of neuropathic pain

The progression of neuropathic pain varies according to the syndrome.

Symptoms of neuropathic pain

Patients with neuropathic pain typically describe their pain as ‘burning’, ‘shooting’, or even ‘electric’. The pain may be associated with odd feelings such as cold, numbness, tingling, pins and needles or itching in the affected area.
Other pain sensations commonly experienced include:

• Allodynia: Pain from a stimulus that is usually not painful;
• Hyperalgesia: An exaggerated response to a painful stimulus (where a stimulus that usually causes mild discomfort causes severe pain);
• Hypoalgesia: A reduced response to a painful stimulus;
• Hypoaesthesia: Reduced touch sensation;
• Paraesthesia: Abnormal but non-painful sensations (such as tingling);
• Dysaesthesia: An abnormal, unpleasant sensation which may arise spontaneously or in response to touch;
• Hyperpathia: An increased response to a painful stimulus, especially a repetitive painful stimulus, in association with an increased pain threshold.

Clinical examination of neuropathic pain

Clinical examination for neuropathic pain involves a careful neurological (nervous system) examination. This aims to identify any areas of sensory change. Different types of stimulus (for example, heat, cold, pinprick and vibration) are applied to the skin, and the patient’s response is recorded as normal, reduced or increased.
Findings on clinical examination vary according to the syndrome. Examination may be completely normal apart from evidence of allodynia, hyperalgesia and hyperpathia, or may help to determine the cause of neuropathic pain, such as evidence of diabetic neuropathy or herpes zoster.

How is neuropathic pain diagnosed?

Investigations may be useful to determine the underlying cause for the  pain, and should be directed to suspected causes. These usually involve blood tests.
Electromyography and nerve conduction studies may be useful in some cases.

Prognosis of neuropathic pain

The prognosis ovaries according to the pain syndrome. However, overall, neuropathic pain is often difficult to treat effectively.

Treatment of neuropathic pain

The treatment of neuropathic pain is difficult. If possible, the underlying cause of pain should be treated, but this is often not the case.
Treatment options may be divided into non-pharmacological and pharmacological.

Non-pharmacological options for pain relief

• Education, supportive counselling and reassurance;
• Exercise or other lifestyle modification strategies;
• Transcutaneous electrical nerve stimulation.

Pharmacological options for pain relief

The pharmacological treatment goal in neuropathic pain is to relieve patient pain and improve quality of life using just a single medication.
Medications used to treat neuropathic pain may be divided into two groups: analgesics; and medications traditionally used to treat other conditions but which are effective in the management of neuropathic pain.

Analgesics

Neuropathic pain is often refractory (unresponsive) to many forms of pain relief usually effective for other forms of pain, including paracetamol, NSAIDs and opioids. However, as some people do respond to simple treatment, it is recommended that a trial of paracetamol, aspirin or another NSAID is the first line in pain relief.
Opioids (such as morphine or oxycodone) may also be trialled. Treatment should begin with low doses only, and then increased until symptomatic relief is achieved without intolerable side effects.

Anticonvulsants

Many anticonvulsant medications (usually used to treat epilepsy) have been trialled in the treatment of neuropathic pain, with varying success.
Gabapentin is a newer drug which has been extensively studied in the management of post-herpetic neuralgia, diabetic neuropathy, phantom limb pain, mixed neuropathic pain, spinal cord injury pain and Guillain-Barre syndrome. In these studies, gabapentin was effective in reducing pain, as well as achieving improvement in sleep, mood and quality of life. Overall, five patients must be treated with gabapentin for one patient to achieve a 50% reduction in pain.
Pregabalin (Lyrica), another new drug with a similar mechanism of action to gabapentin, has a number needed to treat (NNT) of just 4.3 when used to treat post-herpetic neuralgia and diabetic neuropathy. Dosage is usually limited to 300mg daily by adverse effects such as blurred vision.
Other antiepileptic drugs including lamotrigine, valproate, topiramate (Topamax) and carbamazepine have also been studied in the treatment of neuropathic pain, with conflicting results.  

Antidepressants

Tricyclic antidepressants such as amitriptyline have traditionally been a first-line treatment option for the management of neuropathic pain. Low doses are often effective for pain reduction while avoiding troublesome side effects such as dry mouth, blurred vision, urinary retention and low blood pressure. 

Other medications

Antiarrhythmic drugs (e.g. flecainide), ketamine, calcium channel blockers and clonidine may all be trialled when other medications do not adequately control pain. Evidence for the use of these medications is less clear.
Referral to a multidisciplinary pain management centre may also be useful in cases of refractory pain. Some centres are able to offer additional treatment options such as spinal cord stimulation in carefully selected cases.

View the Understanding Neuropathic Pain pamphlet.

 

View the IDPain Screening Tool pamphlet.

 

View the DN4 Patient Questionnaire.

References

1. Cavenagh, J., Good, P. and Ravenscroft, P. ‘Neuropathic pain: are we out of the woods yet?’ Intern Med J. 2006; 36: 251-5.
2. Dworkin RH, Backonja M, Rowbotham MC et al. ‘Advances in neuropathic pain: diagnosis, mechanisms, and treatment recommendations.’ 2003, Arch Neurol 60:1524-34.
3. Goucke CR. ‘The management of persistent pain,’ MJA 2003; 178: 444-447
4. Helme RD. ‘Drug treatment of neuropathic pain’ Aust Prescr 2006;29:72-5
5. Jensen TS, Baron R. ‘Translation of symptoms and signs into mechanisms in neuropathic pain.’ Pain 2003;102:1-8.
6. Pasero, C. ‘Pathophysiology of neuropathic pain.’ Pain Manag Nurs. 2004; 5: 3-8.
7. SPHERE Brochure. ‘Positive Management of Persistent Pain.’ Available online: http://www.spheregp.com.au
8. Therapeutic Guidelines: Analgesic. ed. 2002. Therapeutic Guidelines Ltd