Neuralgia (Greek neuron, "nerve" + algos, "pain") is pain in the distribution of a nerve or nerves, as in intercostal neuralgia, trigeminal neuralgia, and glossopharyngeal neuralgia.
Classification Under the general heading of neuralgia are trigeminal neuralgia (TN), atypical trigeminal neuralgia (ATN), occipital neuralgia, glossopharyngeal neuralgia and postherpetic neuralgia (caused by shingles or herpes). The term neuralgia is also used to refer to pain associated with sciatica and brachial plexopathy.
Atypical (trigeminal)
Atypical trigeminal neuralgia (ATN) is a rare form of neuralgia and may also be the most misdiagnosed form. The symptoms can be mistaken for migraines, dental problems such as temporomandibular joint disorder, musculoskeletal issues, and hypochondriasis. ATN can have a wide range of symptoms and the pain can fluctuate in intensity from mild aching to a crushing or burning sensation, and also to the extreme pain experienced with the more common trigeminal neuralgia. ATN pain can be described as heavy, aching, and burning. Affected individuals have a constant migraine-like headache and experience pain in all three trigeminal nerve branches. This includes aching teeth, ear aches, feeling of fullness in sinuses, cheek pain, pain in forehead and temples, jaw pain, pain around eyes, and occasional electric shock-like stabs. Unlike typical neuralgia, this form can also cause pain in the back of the scalp and neck. Pain tends to worsen with talking, facial expressions, chewing, and certain sensations such as a cool breeze. Vascular compression of the trigeminal nerve, infections of the teeth or sinuses, physical trauma, or past viral infections are possible causes of ATN. In the case of trigeminal neuralgia, the affected nerves are responsible for sensing touch, temperature sensation and pressure sensation in the facial area from the jaw to the forehead. The disorder generally causes short episodes of excruciating pain, usually for less than two minutes and usually only one side of the face. The pain can be described in a variety of ways such as "stabbing", "sharp", "like lightning", "burning", and even "itchy". In the atypical form of TN, the pain presents as severe constant aching along the nerve. The pain associated with TN is recognized as one of the most excruciating pains that can be experienced. Simple stimuli—such as eating, talking, making facial expressions, washing the face, or any light touch or sensation—can trigger an attack (even the sensation of a cool breeze). Attacks may be lone occurrences, clusters of attacks, or constant episodes. Some patients experience muscle spasm, which led to the original term for TN of "tic douloureux" ("tic", meaning "spasm", and "douloureux", meaning "painful", in French).
Glossopharyngeal Glossopharyngeal neuralgia consists of recurring attacks of severe pain in the back of the throat, the area near the tonsils, the back of the tongue, and part of the ear. The pain is due to malfunction of the glossopharyngeal nerve (CN IX), which moves the muscles of the throat and carries information from the throat, tonsils, and tongue to the brain. Glossopharyngeal neuralgia, a rare disorder, usually begins after age 40 and occurs more often in men. Often, its cause is unknown. However, glossopharyngeal neuralgia sometimes results from an abnormally positioned artery that compresses the glossopharyngeal nerve near where it exits the brain stem. Rarely, the cause is a tumor in the brain or neck.
Occipital Occipital neuralgia, also known as C2 neuralgia, or Arnold's neuralgia, is a medical condition characterized by chronic pain in the upper neck, back of the head and behind the eyes.
Mechanisms By understanding the neuroplastic changes following nerve damage, researchers may be able to gain a better understanding of the mechanism of hyperexcitability in the nervous system that is believed to cause neuropathic pain.
Peripheral nerve injury A neuron's response to trauma can often be determined by the severity of the injury, classified by Seddon's classification. In Seddon's Classification, nerve injury is described as either neurapraxia, axonotmesis, or neurotmesis. Following trauma to the nerve, a short onset of afferent impulses, termed "injury discharge", occurs. This occurrence lasts only minutes, but has been linked to the onset of neuropathic pain. When an axon is severed, the segment of the axon distal to the cut degenerates and is absorbed by Schwann cells. The proximal segment fuses, retracts, and swells, forming a "retraction bulb". The synaptic terminal function is lost, as axoplasmic transport ceases and no neurotransmitters are created. The nucleus of the damaged axon undergoes chromatolysis in preparation for axon regeneration. Schwann cells in the distal stump of the nerve and basal lamina components secreted by Schwann cells guide and help stimulate regeneration. The regenerating axon must connect to the appropriate receptors to make an effective regeneration. If proper connections to the appropriate receptors are not established, aberrant reinnervation may occur. If the regenerating axon is halted by damaged tissue, neurofibrils may create a mass known as a neuroma. If an injured neuron degenerates or does not regenerate properly, then the neuron loses its function or may not function properly. Neuron trauma is not an isolated event and may cause degenerative changes in surrounding neurons. When one or more neurons lose their function or begin to malfunction, abnormal signals sent to the brain may be translated as painful signals.
Diagnosis When assessing neuralgia to find the underlying mechanism, a history of the pain, description of pain, physical examination, and experimental examination are required. Pain is subjective to the patient, but pain assessment questionnaires, such as the McGill Pain Questionnaire can be useful for evaluation. Physical examinations usually involve testing responses to stimuli such as touch, temperature, and vibration. Neuralgia can be further classified by the type of stimuli that elicits a response: mechanical, thermal, or chemical. Response to the course of treatment is the final tool used to determine the mechanism of the pain. Additional tools may be used, predominantly in research settings including Laser Evoked Potentials and Quantitative Sensory testing.
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