Several theories exist to explain the possible causes of this pain syndrome. It was once believed that the nerve was compressed in the opening from the inside to the outside of the skull; but newer leading research indicates that it is an enlarged blood vessel - possibly the superior cerebellar artery - compressing or throbbing against the microvasculature of the trigeminal nerve near its connection with the pons. Such a compression can injure the nerve's protective myelin sheath and cause erratic and hyperactive functioning of the nerve. This can lead to pain attacks at the slightest stimulation of any area served by the nerve as well as hinder the nerve's ability to shut off the pain signals after the stimulation ends. This type of injury may rarely be caused by an aneurysm (an outpouching of a blood vessel ); by a tumor ; by an arachnoid cyst in the cerebellopontine angle ; or by a traumatic event such as a car accident or even a tounge piercing.
A large amount of multiple sclerosis patients have TN, but not everyone with TN has MS. Only two to four percent of patients with TN, usually younger, have evidence of multiple sclerosis , which may damage either the trigeminal nerve or other related parts of the brain. It has been theorized that this is due to damage to the spinal trigeminal complex . Trigeminal pain has a similar presentation in patients with and without MS.
Post herpetic Neuralgia , which occurs after shingles , may cause similar symptoms if the trigeminal nerve is damaged.
When there is no structural cause, the syndrome is called Idiopathic .