Idiopathic first bite syndrome treated with Rikkosan: A case report

First bite syndrome (FBS)is characterized by sharp pain in the parotid region at the first bite of a meal which gradually decreases as mastication continues, and is thought to be caused by sympathetic nerve damage. When FBS occurs with no history suggestive of nerve damage, it is classified as idiopathic. A case of idiopathic FBS that was treated effectively with Rikkosan is presented. The patient was an 81-year-old woman who developed sharp pain in the left parotid region with the first bite of every meal in November 2015. With no specific findings, the initial diagnosis was trigeminal neuralgia, but carbamazepine was ineffective. In February 2016, temporomandibular disorder was diagnosed as the cause of masticatory muscle pain and was treated with splinting and loxoprofen sodium, but this was also ineffective. In June 2016, a panoramic radiograph, plain craniocervical magnetic resonance imaging, and blood tests were all negative. Idiopathic FBS was diagnosed and treated by gargling and swallowing Rikkosan before meals and eating bitter or sweet foods first, followed by salty or sour foods. The FBS improved, and after 1 week, she had days with no pain. Rikkosan was discontinued after a month leading to immediate recurrence. The patient was instructed to use half the dose of Rikkosan, which was effective with no side effects. In October 2016, the patient started gargling with Rikkosan. In March 2017, the Rikkosan was discontinued and the dietary strategy was continued with no further recurrence. In this case, idiopathic FBS improved with Rikkosan treatment.