Neuralgia Mechanisms

By Dr Ananya Mandal, MD

The term neuralgia refers to a combination of two words "neuro" meaning relating to nerves and "algesia" meaning sensitivity to pain. Neuralgia therefore describes pain felt in one or more nerves. The pain sensation may arise without stimulation of pain receptors and instead as the result of abnormal function or structure of nerves.

Mechanism of neuropathic pain or neuralgia

There are four possible mechanisms by which pain due to neuralgia may occur and these include dysfunction of the ion channel gate; mechanically sensitive neuronal fibres generating an ectopic signal; the crossing of signals from touch fibres to pain fibres and dysfunction caused by damage to the central nervous system.

Causes of neuralgia

Neuralgia may result from nerve damage. Seddon's classification is used to classify or grade the severity of injury to the nerves. Under this classification, nerve injury can be classified as:

  • Neurapraxia, a disorder of the peripheral nervous system
  • Axonotmesis, disruption of the neuronal axon
  • Neurotmesis, severe damage caused by disruption of both the nerve and the nerve sheath

When a nerve is traumatised or injured, there is a short term increase in nervous impulse which is referred to as injury discharge. This can last for only a few minutes or may lead to the beginning of neuropathic pain.

The level of pain is assessed using pain assessment scales such as the McGill Pain Questionnaire. It is important to qualify and quantify the pain before diagnosis is confirmed and in order to assess the efficacy of treatment. Qualitative senses testing is also done using the Quantitative sensory testing (QST) procedure.

Neuralgia is classified according to the stimulus that elicits a pain response. This could be different for different neuralgias. Sometimes pain may be stimulated by mechanical pressure and in other cases, heat or chemicals may stimulate a response.

Symptoms of neuralgia

There are different types of neuralgia including trigeminal neuralgia, atypical trigeminal neuralgia, occipital neuralgia and postherpetic neuralgia. The major symptoms seen in nearly all types of neuralgia include:

  • Pain - The pain can be excruciating and is often described as sharp, stabbing, burning, itching or electric shock-like sensations. There may also be a constant dull ache over the area.
  • Nausea due to excessive pain
  • Sleep deprivation due to pain
  • Hypersensitivity of the skin, which may feel painful even when touched with a feather touch or exposed to a breeze
  • Disability
  • Malnutrition
  • Depression and anxiety

Reviewed by Sally Robertson, BSc

Sources

  1. http://www.ucdmc.ucdavis.edu/pain/Pain%20Resources/QPostHerpeticNeauralgia_NSingh.pdf
  2. http://www.nhs.uk/conditions/trigeminal-neuralgia/Pages/Introduction.aspx
  3. http://www.nhs.uk/conditions/postherpetic-neuralgia/Pages/Introduction.aspx
  4. http://www.bsom.org.uk/PatientInformation/trigeminalneuralgialeaflet.pdf

Further Reading

Last Updated: Jan 14, 2014

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