TRIGEMINAL NEURALGIA

Trigeminal neuralgia (TN), also known as tic douloureux, is sometimes described as the most excruciating pain known to humanity. The pain typically involves the lower face and jaw, although sometimes it affects the area around the nose and above the eye. It defined as a sudden, severe, brief, lancinating episodic facial pain that is usually unilateral, recurring electric shock-like, and provoked by light touch. It is reported that 150,000 people are diagnosed with trigeminal neuralgia (TN) every year. While the disorder can occur at any age, it is most common in people over the age of 50. The National Institute of Neurological Disorders and Stroke (NINDS) notes that TN is twice as common in women than in men.

Strong empirical evidence indicates that vascular compression of the trigeminal nerve root is associated with trigeminal neuralgia in about 95% of patients. Popular hypotheses include a combination of central demyelination of the nerve root entry zone and reinforcing electrical excitability (the ignition hypothesis). This demyelination then leads to an impairment of the nociceptive system. Trigeminal neuralgia cases are also associated with multiple sclerosis plaques or lacunar infarctions within the brain stem trigeminal system or cerebellopontine mass lesions. 

The diagnostic criteria for trigeminal neuralgia include pain which is unilateral, bilateral in 3% of patients, of sudden onset, electric shock-like, sharp, shooting pain lasting a few seconds to minutes. It can be provoked by light touch to the face, eating, cold winds, or vibrations. Rarely associated with history of other chronic pain or migraine. Some forms have more continued aching background pain after main attack. Rarely associated with autonomic features. The red flags associated with trigeminal neuralgia are sensory changes, deafness or other ear problems, difficulty achieving pain control, poor response to carbamazepine, history of any skin lesions or oral lesions that could lead to perineural spread, ophthalmic division only or bilateral as suggestive of benign or malignant lesions or multiple sclerosis, age of onset under 40 years, optic neuritis.

The most useful investigation to diagnose trigeminal neuralgia is an MRI scan of the brain with and without contrast, which is used to rule out other potential causes of pain if the diagnosis is not clear cut or if red flags are present. MRI is very sensitive in identifying sinusitis, extracranial masses along the course of the trigeminal nerve, any pathological enhancement of the trigeminal nerve that could indicate perineural spread of malignancy, cavernous sinus masses and demyelination plaques that might indicate multiple sclerosis. 

The biochemical investigations are done to diagnose any reductions in white blood cell count, hyponatraemia, a complete blood count at baseline with differential, serum electrolytes, and liver function tests to monitor for potential drug toxicity over time. For patients taking enzyme inducing drugs, the National Institute for Health and Care Excellence (NICE) recommends a full blood count, measurements of electrolytes, liver enzymes, and vitamin D levels, and other tests of bone metabolism (for example, serum calcium and alkaline phosphatase) every two to five years.

There are several effective ways to alleviate the pain, including a variety of medications. Medications are generally started at low doses and increased gradually based on patient’s response to the drug. Carbamazepine, an anticonvulsant drug, is the most common medication that doctors use to treat TN. In the early stages of the disease, carbamazepine controls pain for most people. Possible side effects include dizziness, double vision, drowsiness and nausea. Gabapentin, an another anticonvulsant drug, which is most commonly used to treat epilepsy or migraines can also treat TN. Oxcarbazepine, a newer medication, has been used more recently as the first line of treatment. It is structurally related to carbamazepine and may be preferred, because it generally has fewer side effects. Other Medications include baclofen, amitriptyline, nortriptyline, pregabalin, phenytoin, valproic acid, clonazepam, sodium valporate , lamotrigine, topiramate, phenytoin and opioids. There are drawbacks to these medications, other than side effects. Many of these drugs can have a toxic effect on some patients, particularly people with a history of bone marrow suppression and kidney and liver toxicity. 

Surgical treatment is divided into two categories: 1) open cranial surgery 2) lesioning procedures. In general, open surgery is performed for patients found to have pressure on the trigeminal nerve from a nearby blood vessel, which can be diagnosed with imaging of the brain, such as a special MRI. In contrast, lesioning procedures include interventions that injure the trigeminal nerve on purpose, in order to prevent the nerve from delivering pain to the face. The effects of lesioning may be shorter lasting and in some keys may result in numbness to the face.

Percutaneous radiofrequency rhizotomy treats TN through the use of electrocoagulation (heat). It can relieve nerve pain by destroying the part of the nerve that causes pain and suppressing the pain signal to the brain. The surgeon passes a hollow needle through the cheek into the trigeminal nerve. A heating current passed through an electrode, destroys some of the nerve fibers. Percutaneous balloon compression utilizes a needle that is passed through the cheek to the trigeminal nerve. The neurosurgeon places a balloon in the trigeminal nerve through a catheter. The balloon is inflated where fibers produce pain. The balloon compresses the nerve, injuring the pain-causing fibers, and is then removed. Percutaneous glycerol rhizotomy utilizes glycerol injected through a needle into the area where the nerve divides into three main branches. The goal is to damage the nerve selectively in order to interfere with the transmission of the pain signals to the brain. Stereotactic radiosurgery  delivers a single highly concentrated dose of ionizing radiation to a small, precise target at the trigeminal nerve root. This treatment is noninvasive and avoids many of the risks and complications of open surgery and other treatments. Neuromodulation used for patients with TN, another surgical procedure can be done that includes placement of one or more electrodes in the soft tissue near the nerves, under the skull on the covering of the brain and sometimes deeper into the brain, to deliver electrical stimulation to the part of the brain responsible for sensation of the face.