What is Neuropathic Pain?

What is Neuropathic Pain?

Neuropathic pain disorders are a set of pain conditions resulting from disorder or injury to the nervous system. The human nervous system is divided into two general parts: the central nervous system, comprising the brain and spinal cord, and the peripheral nervous system, including nerves that go to the limbs, trunk, face and all outlying areas of the body. When nerves of the peripheral system sense pain from mechanical, chemical or thermal sensations, they relay the sensation to the central nervous system for processing. Additionally, the spine and brain command a network a nerves conducting sensation along the back, neck, head and face. Damage to nerves of the peripheral or central nervous system can cause pain signals to be sent to the brain, which may result in the chronic pain condition known as neuropathic pain.

Neuropathic pain may manifest as continuous or episodic, with episodic attacks described as an electric shock and continuous attacks often experienced as feelings of prolonged aching, burning, sensitivity or coldness. Neuropathic orofacial pain conditions refer to those with symptoms that primarily affect a patient's mouth and face.  Orofacial means of the mouth or face.

Trigeminal Neuralgia

The most common orofacial neuropathic pain condition is trigeminal neuralgia, a disorder of the trigeminal or 5th cranial nerve, which causes sudden, severe shock-like pain in or around the face. Episodes typically last several seconds, though they can last up to two minutes, and may repeat in succession and throughout the day.

The trigeminal nerve is one of 12 pairs of cranial nerves, the nerves that emerge directly from the brain. The trigeminal nerve has three branches reaching throughout the face and oral cavity. The upper branch is responsible for sensations for the scalp, forehead and front of the head. The middle branch is responsible for sensations in the cheek, upper jaw, top lip, top teeth and gums, and side of the nose. The lower branch is responsible for sensations of the lower jaw, lower teeth and gums, and bottom lip. More than one branch may be affected by a disorder of the nerve, and sufferers may experience pain on both sides of the head and neck, although typically only one side is affected by an episode at a time.

There are other conditions that affect nerves of the central nervous system and cause orofacial neuropathies, such as glossopharyngeal neuralgia, occipital neuralgia, vagal neuralgia and superior laryngeal neuralgia. These orofacial neuropathies are less common, though they are thought to be caused in the same way as trigeminal neuralgia, which is a pressure applied, often by a blood vessel, to the associated nerve as it exits the brain.

An episodic attack of trigeminal neuralgia may be triggered by contact with any of the parts of the face, jaw, mouth and head mentioned above. The condition may become worse over time. Pain may at first be experienced in a small area of the face, later spreading. Episodes can occur for some patients for days, weeks or months and then subside for months or years. If the condition worsens, time between episodes may become shorter and less frequent.

Trigeminal neuralgia has been divided into two types. In Type 1 trigeminal neuralgia, more than half of the pain experienced is shock-like pain described as sudden, sharp, burning or stabbing. In Type 2 trigeminal neuralgia, more than half of the pain experienced is constant pain that is aching, burning or coldness, numbness, or a "pins and needles" sensation. Type 2 trigeminal neuralgia is also known as pre-trigeminal neuralgia as it eventually develops into the classic form of trigeminal neuralgia characterized by intermittent shock episodes.

Atypical Odontalgia

Also among the more common forms of neuropathic orofacial pain is atypical odontalgia. This condition, also known as phantom tooth pain, may follow a dental procedure such as a root canal or an extraction, and is experienced as a pain like a toothache with no actual problem in the tooth.

Oral Nerve Injury

Neuropathy to the inferior alveolar nerve or the lingual nerve occurs most often as a complication of a dental or medical procedure. Tooth extraction, usually of the wisdom teeth, is the leading cause of lingual and inferior alveolar nerve damage. It may also occur as a result of anesthetic injections for oral procedures. The result is pain and burning sensation, numbness or tingling of the tongue, mouth or lower lip.

Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS), also called causalgia or Reflex Sympathetic Dystrophy Syndrome, is a rare chronic pain condition originating from a disorder of the nervous system. CRPS can affect the craniofacial region, though is more common in the arms and legs. CRPS I is associated with tissue injury and CRPS II is associated with nerve injury. The pain is described as a continuous burning pain and may be accompanied by changes in skin temperature, color and texture, increased skin sensitivity and swelling and stiffness.