Neuropathic pain, specifically conditions affecting the head and neck, may result from various of injuries, illness or disorder.
Common causes of trigeminal neuralgia include:
- Nerve compression: Trigeminal neuralgia, the most common neuropathic pain condition, results from disorder of the trigeminal nerve. It is believed that the most common cause of this condition is a blood vessel pressing on the nerve, wearing away at the nerve's protective coating known as the myelin sheath. Damage done by compression of the nerve can result in deterioration of function whereby abnormal signals are sent to the brain.
- Tumors: A tumor pressing against a nerve may cause deterioration of the myelin sheath. A tumor at the base of the brain may affect the trigeminal nerve, causing pain in the head, neck and face.
- Multiple sclerosis: This auto-immune disease affects the central nervous system, causing inflammation and permanent damage to the myelin sheath of nerves of the brain and spinal cord. The myelin sheath is like insulation for the nerve, and if this insulation is damaged, the nerve can cause severe pain in the head, neck and face as part of a broad spectrum of signs and symptoms.
- Physical injury: An accident or other cause of injury can damage nerves so that they relay messages of pain to the brain. A damaged nerve can continue to refer pain signals to the brain even after an injury is otherwise healed. Common causes of injury to the trigeminal nerve include dental or surgical procedures, infection in the oral cavity and injury to the face.
The cause of atypical odontalgia is unknown, though the condition may be a result of nerve deafferentation, which is the interruption or elimination of nerve fibers. This theory is supported by atypical odontalgia patients where onset of the condition occurs following a dental procedure such as a root canal or extraction. However, there are cases of atypical odontalgia where no procedure has been performed and no known cause identified.
Oral nerve injury is a common complication of dental procedures including extraction of the third molar, also known as the wisdom tooth. It can also occur as a result of an injection of local anesthetic for procedures including fillings, crowns and root canals. Incorrect implant placement may also damage the inferior alveolar or lingual nerve. This damage to these nerves running along the lower jaw can cause pain, tingling or numbness in the tongue, mouth and lower lip.
Complex regional pain syndrome (CRPS) is thought to originate by an injury to tissue or nerves and then perpetuated by irregular behavior in the sympathetic nervous system, a component of the autonomic nervous system responsible mainly for mobilizing the body's resources under stress and triggering the fight-or-flight response.
Recent research suggests that in cases of CRPS, when an injury to tissue or nerve is sustained, an unknown mechanism results in the sympathetic nervous system maintaining active pain pathways. Another theory suggests that CRPS may be a disruption of the healing response whereby an injury triggers an immune response resulting in inflammation, redness and swelling. More than likely, CRPS is the result of multiple causes occurring at once.