Introduction
Idiopathic facial palsy is a common presentation to the ENT out-patient department, with variable degrees of both severity and resolution. Patients usually present with a facial droop, and can additionally have issues with eye closure, lack of tearing, change in taste and hyperacusis.
Synkinesis is a less common symptom, but patients can present with varying involuntary muscular movements accompanying voluntary ones. Oculostapedial synkinesis is one of the rarer forms of synkinesis and can potentially be overlooked, despite the frustrating symptoms for the patient.
This case report highlights the condition of oculostapedial synkinesis, and reviews how to appropriately investigate and manage affected patients.
Case report
A 56-year-old gentleman developed a sudden lower motor neurone facial palsy in October 2015. The facial palsy was classified as House–Brackmann grade VI,Reference House and Brackmann1 and was initially treated with high-dose prednisolone in the community. The patient, who is a retired forge worker, had no other medical co-morbidities of note; he has no allergies and is a non-smoker.
He was referred by his general practitioner to the neurology department, as the facial palsy did not show any signs of improvement initially. Gradually, the facial palsy improved until he was left with a grade II persistent palsy.
An incidental contralateral meningioma was detected on cross-sectional imaging, and the patient was referred to the neurosurgeons who adopted a conservative monitoring approach. However, the neurosurgeons referred this gentleman to ENT, as despite the facial nerve paralysis improvement, he had a persistent sensation of creaking in the ear and an inability to hear when eating. On further questioning, he complained of a distortion of hearing upon eye closure. He had no other associated otological symptoms; no hearing loss, tinnitus, otalgia or otorrhoea.
A magnetic resonance imaging (MRI) scan of the brain and internal auditory meatus was initially undertaken by the neurologists, to assess for underlying structural pathology. This did not identify any facial nerve pathology, but revealed an incidental contralateral, left-sided cavernous sinus intradural meningioma.
The neurology team undertook routine blood investigations, including a full blood count, a coagulation screen, and tests of thyroid function, urea and electrolyte, erythrocyte sedimentation rate, liver function, and vitamin D; the levels were all within the normal ranges. In addition, a test of angiotensin-converting enzyme levels was undertaken to rule out sarcoidosis, and a serum Borrelia burgdorferi test was conducted to rule out Lyme's disease; both of these test results were negative.
A repeat MRI scan of the facial nerve was organised in the otology clinic. This revealed enhancement of the horizontal portion of the facial nerve bilaterally; this finding was deemed to be insignificant. There was no definite enhancement within the right geniculate ganglia, and the VIIth and VIIIth cranial nerves were otherwise normal bilaterally.
Pure tone audiometry revealed normal hearing thresholds bilaterally. Impedance audiometry showed a type A tympanogram, with no notable variance on facial movement. Stapedial reflexes were normal.
The patient was referred on, for specialist physiotherapy with an expert on facial palsy. This conservative management did not improve the patient's symptoms, and the patient was keen to consider surgical intervention.
A right-sided tympanotomy and transection of the stapedial tendon was proposed. The patient was warned to expect increased sensitivity to loud noises post-operatively, and was made aware of the potential complications of: intra-operative facial nerve injury, a change in taste due to chorda tympani damage, tinnitus, vertigo and a decrease in hearing. The patient opted to go ahead with the tympanotomy and transection of the stapedial tendon. The surgery was uneventful, with no complications.
Post-operatively, the patient had complete resolution of otological symptoms immediately after surgery. The incidental meningioma is being followed up in the lateral skull base clinic with interval imaging, and requires no current intervention.
Discussion
The facial nerve is complex. It supplies motor fibres to the muscles underlying facial expressions and the stapedius muscle. Additionally, it has: sensory fibres to the external ear canal via the post-auricular nerve; viscerosecretory fibres to the lacrimal, submandibular and sublingual glands; and gustatory fibres in the form of the chorda tympani. The stapedial muscle has a protective role against loud acoustic stimuli. In the presence of a loud noise, the stapes is pulled posteriorly by the stapedial muscle and tendon, restricting ossicular chain movement and thus limiting conduction of the sound energy to the inner ear.
Although the majority of facial palsies improve, up to 30 per cent of cases will continue to have some residual asymmetry. Patients may also have issues with myoclonus, hyperkinesis, synkinesis and spasm.Reference Watson, Glover, Allen and Irving2 Synkinesis is the presence of abnormal involuntary movements alongside voluntary muscle movements. An example of this, other than oculostapedial synkinesis, is synkinesis of the orbicularis oculi and orbicularis oris muscles, or eye closure on moving the mouth.
There are various theories proposed as to why synkinesis develops. Schwarze et al. have discussed three peripheral theories, as follows.Reference Schwarze, Hirsch and Johnson3 Firstly, anomalous regeneration occurs at a site of injury, causing cross-branching of developing axons into inappropriate nerve tubules, which results in facial nerve fibres aberrantly innervating facial muscles and causing involuntary action. Secondly, ectopic excitation occurs due to lowered depolarisation thresholds induced by injury. Thirdly, excess intermuscular innervation develops as a result of motor end plate axon sprouting, causing anastomoses that connect peripheral nerve branches. Schwarze et al. also discuss a central theory that was proposed by Ferguson,Reference Ferguson4 wherein nerve injury causes retrograde changes of the cells in the facial nucleus, which lead to a hyper-excitable environment for neural activity.
The symptoms specifically linked to oculostapedial synkinesis are dullness to the hearing,Reference Schwarze, Hirsch and Johnson3 or a low-pitched tinnitus described as ‘tympanic noise’,Reference Kim and Fukushima5 which are associated with facial movement and particularly eye closure. Oculostapedial synkinesis has been described following facial palsy, as in the cases reported by Donne et al.Reference Donne, Homer and Woodhead6 and Kang et al.Reference Kang, Hong, Chung and Hong7 The condition has also been described without facial palsy in a 30-year-old female patient, in which the symptoms spontaneously resolved.Reference Fujiwara, Furuta and Fukuda8 In all documented cases, the treatment involved surgical resection of the stapedial tendon.
• Synkinesis is the involuntary movement of muscles accompanying voluntary movements, and can occur after facial nerve palsy
• Oculostapedial synkinesis is a rarer form of synkinesis, but can present with hearing distortion on facial movement
• Oculostapedial synkinesis is a clinical diagnosis with subjective symptoms
• Objective evidence of stapedial synkinesis includes variance of tympanic membrane compliance with facial movement
• Transection of the stapedial tendon has been shown to resolve oculostapedial synkinesis symptoms
Oculostapedial synkinesis is a subjective phenomenon; it is difficult to show evidence for it objectively on examination. However, variance in tympanic membrane compliance has been described. Schwarze et al. found that tympanometry demonstrated variability in tympanic membrane compliance with voluntary facial movement in their oculostapedial synkinesis patient.Reference Schwarze, Hirsch and Johnson3 A study by Kim and Fukushima found that 87 per cent of the 47 patients included in their report had changes in middle-ear compliance when closing their eye voluntarily or during orbicularis oculi spasm.Reference Kim and Fukushima5 Other case reports have also found evidence of compliance change on impedance audiometry with facial movement.Reference Donne, Homer and Woodhead6–Reference Fujiwara, Furuta and Fukuda8
Competing interests
None declared
