Sir, we wish to report an unusual case of facial nerve palsy. A 33-year-old female presented complaining of swelling on the left-hand side of her face which was visibly swollen over her cheek and tracked down to her submandibular region. Endodontic treatment had recently been carried out on tooth 25, but the tooth was asymptomatic prior to obturation and was asymptomatic on presentation.

Intra-orally, no sinus was evident, and teeth 34 and 38 were tender to percussion. There were heavy plaque deposits in the lower arch, and the gingivae appeared erythematous. It was felt that there may be a periodontal component to the patient's pain and swelling, so one cartridge of 2% lidocaine hydrochloride with 1:80,000 adrenaline was administered as an inferior dental block (IDB) using an aspirating syringe. Ultrasonic debridement was carried out on the lower arch and the patient was prescribed 500 mg amoxicillin and 200 mg metronidazole as local drainage was not possible. The patient was to be reviewed the next day, and advised to seek medical advice if the swelling became worse overnight.

The patient then presented to the local A&E department in the early hours of the morning with no toothache but left sided facial nerve weakness, pulsing facial pain and a sore throat, which started around 1-2 hours whilst at work, post-administration of the IDB. On clinical examination, there was no obvious swelling or cervical lymphadenopathy, but a clinically apparent dry left eye and left sided facial nerve weakness. Teeth 24 and 25 were slightly tender to percussion but no other abnormalities were detected. A diagnosis of left-sided facial nerve palsy was reached, and the patient was prescribed low dose oral steroids to take once a day for seven days and Xailin and Hylo-forte eye drops to use morning and night to prevent any eye dryness. She was advised to use transpore tape and a patch to cover the affected eye. However, it was unclear if the patient's symptoms were due to the local anaesthetic she received at her dental appointment or due to an alternative coincidental cause. The patient's symptoms have now thankfully resolved.

Facial palsy following local anaesthetic administration has been reported to have an incidence between 1:42 and 1:750,000,1 and can have several causes, including direct trauma, injection into a lobe of the parotid gland near where the facial nerve branches, neurotoxic effects of the local anaesthetic, and also type I (immediate) and type IV (delayed) hypersensitivity reactions, with the onset of facial nerve paralysis sometimes delayed for over two hours.