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Chronic pain is one of the most common reasons for medical visits, cases of which make up anywhere from 20-50% of patients seen in primary care clinics1. Chronic pain can be subdivided into two classes of pain; (1) neuropathic pain caused by abnormal functioning or injury to nerves of the central or peripheral nervous system, and (2) nociceptive pain, which is pain caused by external stimuli, injury, inflammation and trauma. It’s estimated that as many as 1.6 – 8.2% of the general population suffers from some type of neuropathic pain2.
A relatively common cause of neuropathic pain is trigeminal neuralgia (TGN), a condition which causes intermittent attacks of severe, sharp, stabbing pain along the nerve branch distributions in the face3, 4. TGN is one of the most common causes of facial pain, and is especially common amongst the elderly. Approximately 15,000 new cases of TGN occur annually in the United States alone, and this incidence of the disease increases with age3. Attacks typically affect just one side of the face, and pressure on certain trigger zones, or certain trigger activities like chewing, talking, or smiling, may induce an attack.
The trigeminal, or 5th cranial, nerve carries sensory stimuli from the face, and is subdivided into three branches; the ophthalmic (V1), maxillary (V2), and mandibular (V3)3. The ophthalmic branch reports sensation from the forehead and top of the face, the maxillary reports sensory stimuli from the middle of the face under the eyes and along the cheeks and nose, while the mandibular branch innervates the bottom of the face around the mouth and chin.
Most cases of TGN are caused by compression of the trigeminal nerve root inside of the skull, usually by loops of abnormal blood vessels3. This is classified as ‘classic’ TGN4. Other vascular abnormalities, tumors and cysts can cause compression as well. When compression is caused by anything not vascular, the condition is classified as ‘secondary’ TGN4. Connecting compression with pain is not currently well understood, however compression is thought to cause destruction of the insulating myelin sheath that surrounds the nerve, which may in turn cause abnormal electrical signaling that can include pain3.
Diagnosis and Treatment
Diagnosis of TGN is made by a physician on the basis of clinical symptoms and a physical exam3. If TGN is suspected, further investigation with radiologic imaging, such as CT or MRI, can be done to rule out possible secondary causes4. Alternatively, electrical trigeminal reflex tests can be performed to distinguish between classic and secondary TGN3.
Treatment for TGN begins with pharmacologic therapy in an effort to control the pain1. A variety of neuropathic medications exist for first-line treatment of TGN, all of which have been proven to be effective in managing pain for many patients4. Unfortunately, however, some cases of TGN do not respond to medical therapy, and may require surgical intervention. Surgical interventions include micro-vascular decompression, or removal of vascular structures from the nerve root, and procedures to destroy portions of the nerve root conducting pain such as rhizotomy and gamma-knife radiosurgery3, 4.
1 Bajwa, Z.; Smith, H. (2012). Overview of the treatment of chronic pain. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA.
2 Brown, G. (2011). Neuropathic Pain. Ferri: Ferri’s Clinical Advisor, 1st Ed. MD Consult Web site, Core Collection.
3 Bajwa, Z.; et al. (2012). Trigeminal Neuralgia. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA.
4 Dotson II, W. (2011). Trigeminal Neuralgia. Ferri: Ferri’s Clinical Advisor, 1st Ed. MD Consult Web site, Core Collection.