Transient glossopharyngeal nerve palsy due to mandibular nerve block

Background

Local anaesthesia is a standard procedure in everyday dental practice in order to attain analgesia. Although it is considered generally safe, complications do occur. Reporting potential risks associated with oral injections and recognising the likelihood of complications can help reduce the incidence of such side effects.1 Systemic complications are attributed to accidental intravascular injection but are considered rare. Local complications are either due to direct nerve damage or to neurotoxicity of the local anaesthetic. Direct nerve trauma is thought to be caused when needle barb ruptures connective tissues and damages nerve fibres or if intraneural haematoma develops due to trauma of vasa nervorum. In both cases, although complete nerve damage (neurotmesis) is rarely reported, recovery might be delayed until remyelination (in cases of neurapraxia) and/or axonal regeneration (in cases of axonotmesis) is completed. In most cases, where neurological symptoms occur but only last for couple of hours, chemical damage to the nerve seems to be a more plausible explanation.

It is estimated that 1 in 20 000–850 000 patients will present nerve involvement after mandibular nerve block, with articaine been associated in more cases relatively to other agents.2 In most published papers, lingual nerve trauma accounts for 70% of cases, and this is attributed to its very superficial position under the mucosa, near the site of needle penetration for mandibular nerve block, resulting in numbness in the tongue. In the rest cases of sensory sequelae, inferior alveolar, mental and rarely chordi tympani nerves are involved.3 Other less common nerve injuries have been reported, such as facial nerve palsy, either of immediate or late onset, probably because of anatomic variant of the nerve, transient amaurosis, an almost terrifying complication due to infusion of the anaesthetic drug in the central retina artery through retrograde flow in the maxillary artery, diplopia attributed to flow of the drug in the cavernous sinus and paralysis of nerves III, IV and VI, Horner’s syndrome due to blockade of stellate ganglion and even deafness due to cochlear nerve dysfunction.4 It is generally agreed that the higher the concentration of anaesthetic, the higher the risk of neurological complications.5

Case presentation

We report a case of pharyngeal muscles palsy that occurred about 30 min after administering local anaesthetic for right mandibular nerve block for routine dental procedure (scaling and root planing for periodontitis treatment). The patient was a middle aged woman, a doctor by profession, with a free medical history and not mentioning any allergies. Articaine 4% plus epinephrine were initially administered (40 mg/mL plus 1:100000, respectively, one ampoule of 1.7 mL) with a needle 0.30×25 mm 30G. After 5–10 min, because of inadequately achieved anaesthesia in tongue, a further administration of mepivacaine 3% (30 mg/mL one ampoule of 1.8 mL) was infused in the same spot as the first one. After 5 min, anaesthesia in the distribution of inferior alveolar nerve was achieved, but not in the tongue (lingual nerve). The dental procedures were completed with slight annoyance, and the patient left the dental office. Half an hour later, the patient felt difficulty in swallowing saliva and her speech became nasal. Self-inspection revealed uvula deviation to the left. She felt numbness in front of the helix and tragus but never felt numbness in tongue. No facial palsy or diplopia were observed.

Investigations

The patient, being a doctor, was inspecting herself and was in constant contact with the dentist. She avoided drinking or eating anything to protect the airways. The symptoms lasted for about 3 hours and gradually subsided without any special treatment.

Differential diagnosis

This is the first case of transient palsy of pharyngeal musculature occurring as a complication of mandibular nerve block in the pterygomandibular space. It is questionable which nerve was injured. The fact that numbness occurred in the proximal area of the ear could implicate almost four cranial nerves: trigeminal, facial, glossopharyngeal nerve (GPN) and vagus nerve (VN). Since no facial palsy was observed, VII injury was ruled out. Mandibular nerve, the third branch of trigeminal nerve, may have accounted for numbness in the area, but it is almost impossible to have produced uvula deviation due tensor palatine muscle palsy only. Furthermore, the fact that no numbness occurred in tongue implies that finally lingual nerve was not affected by the local anaesthetic. Therefore, numbness around the ear and uvula deviation should probably be attributed to VN and GPN.

Outcome and follow-up

Eventually, as it happens in most cases of nerve palsies after local anaesthesia, symptoms subsided without special treatment and without any residues.