The nature of trigeminal neuralgia (TN) is fluctuating and patients can experience periods of complete remission of pain as well as periods with excessive pain. TN is often triggered by innocuous intra- and extraoral stimuli such as chewing. Since the first-line prophylactic drugs, i.e. carbamazepine and oxcarbazepine, are administered orally, medical treatment of TN can be problematic in periods of exacerbation. In cases of severe exacerbation, patients oftentimes become dehydrated and anorectic as eating and drinking will evoke pain. Treatment with drugs administered intravenously is needed in such situations. Phenytoin was the first drug to be used for TN but it is rarely used as long-time preventative because of frequent side-effects associated with long-term use. However, phenytoin has the advantage over other drugs, that it can be administered also intravenously as fosphenytoin (the prodrug of phenytoin).

By clinical experience the efficacy is very good. However, evidence of the treatment is lacking as only case reports including a total of 5 patients described the effects and side effects with pain relief lasting two days. By providing solid observational evidence, the treatment can be considered for incorporation in local and international treatment guidelines.

The aim of the study is to test the hypothesis that fosphenytoin loading reduces TN pain with at least 50 % in 80% of patients with trigeminal neuralgia experiencing exacerbation of TN pain.

The study is a descriptive prospective observational pilot study with 3 months followup period.

Inclusion Criteria:

• Age 18 years or older.
• Must be able to give signed informed consent prior to study entry.
• Must fulfill the ICHD-3 diagnostic criteria for TN. Both patients with purely paroxysmal TN and patients with TN with concomitant persistent facial pain will be included.
• MRI of the brain, brainstem and trigeminal nerve or patient is willing to undergo MRI in the days and weeks following admission.
• Must be able to adhere to the study protocol and understand either Danish or English.

Exclusion Criteria:

• Psychiatric or mental illness or condition that might interfere with the ability of the patients to fill in the Informed Consent.
• Contraindications for phosphenytoin loading such as sick sinus syndrome, atrioventricular block and hepatic insufficiency.

Patients with trigeminal neuralgia admitted for fosphenytoin loading due to acute exacerbations of trigeminal neuralgia pain.