Abstract
A report of two female patients with persistent unilateral retroauricular pain and cranial synkinesis following Bell's palsy. Pain occurred during menses in the first patient and was exacerbated by menses in the second patient. Retroauricular pain often precedes or follows Bell's palsy. Pain normally disappears within 2 weeks from the onset of paralysis. Neurological examination, brain magnetic resonance imaging (MRI), computed tomography of the head and cranial electrophysiological testing were performed. The first patient had severe right retroauricular pain during her menses for several years following Bell's palsy. Her brain MRI showed non-specific T2 white matter hyperintensities. On her electromyogram she had facial synkinesis with tonic motor unit discharges on her right orbicularis oris and mentalis muscles during sustained eye closure. The second patient reported hearing a sound over her left ear when she blinked or protruded her jaw after Bell's palsy. She had ipsilateral retroauricular pain, exacerbated during menses. Her brain MRI was normal. Electromyogram showed facial synkinesis. Chronic retroauricular pain, occurring or exacerbated during menses, may be a rare complication of Bell's palsy. It can be associated with facial subclinical synkinetic dystonia and trigemino-facial synkinesis.
Introduction
Referred otalgia is characterized by ear pain, originating in extra-auricular structures. The most common example is the ear pain experienced by patients with acute pharyngitis and after tonsillectomy. Paroxysmal ear pain is typical of geniculate and great auricular neuralgias (1, 2). Less frequent causes of referred periauricular pain are cervical spondylosis, temporomandibular joint dysfunction (TMJ), paroxysmal hemicrania, extra joints between head and neck, extratrigeminal ice pick status, Eagle syndrome, neck–tongue syndrome, red ear syndrome and primary yawning headache (3–11). Periauricular pain is often reported by patients immediately preceding Bell's palsy, or within the first 2 weeks of onset of facial paralysis. Two female patients are reported with severe retroauricular pain, appearing during menses in the first patient and exacerbated during menses in the second patient as a chronic complication of Bell's palsy. Both exhibited cranial synkinesis.
Case report
Case 1
A 40-year-old female was referred for neurological evaluation because of head pain. Although she had remote history of occasional global headaches, she had developed intense pain behind her right ear, beginning simultaneously with Bell's palsy on the same side, 4 years earlier. Over time the pain disappeared, to reappear only with her menses. Common analgesics did not relieve her pain. Her facial paralysis had been complete and associated with loss of taste. She never recovered from her paralysis and instead, in a few months, she developed involuntary twitching over the right corner of her mouth every time she blinked. She described an unpleasant facial pressure sensation felt during her menses on the side of the paralysis. She had a history of irritable bowel syndrome. Her mother suffered from migraines, but there was no other history of familial disorder. Her general physical examination was normal. There was near complete paralysis of the right facial muscles, which appeared retracted. Blinking or winking resulted in twitching of the right facial muscles, more noticeable around her mouth. Sensory examination of the face was normal with no pain trigger points. Swallowing or chewing did not cause pain. On light eye closure rapid, rhythmic, symmetric tremors of her lids were observed accompanied by quick and also symmetric, short-range horizontal eye movements visible under the lids (blepharoclonus). The involuntary lid movements were abolished by forceful eye closure. Visual acuity, visual fields, ocular saccades, smooth pursuit and optokinetic responses were normal. There was no gaze paralysis. Her pupils were equal and reacted normally to light and to near objects. Her ocular fundi revealed no retinal, vascular or optic nerve pathology. Examination of her ears and the rest of her neurological examination were also normal. CBC, chemistries, computed tomography (CT) of the brain and magnetic resonance imaging (MRI) of the brain were normal. Cerebrospinal fluid (CSF) analysis was normal. No oligoclonal bands were detected in the CSF. The right R1 component of the blink reflex was delayed. The right mental nerve response was unobtainable. Blink synkinetic facial movements were documented by electromyogram (EMG). In addition, tonic motor unit discharges, with amplitude of 600 µV, were recorded at the orbicularis oris and mentalis muscles during sustained eye closure. No significant difference on her EMG abnormalities were observed in follow-up testing at different times of her menstrual cycle. She was prescribed amitriptyline and subsequently gabapentin, with no improvement of her cyclic pain or right facial discomfort. Valproate ameliorated her symptoms, but was discontinued due to liver toxicity. Three years later her catamenial retroauricular pain has diminished in intensity, responding to the administration of acetaminophen.
Case 2
A 38-year-old female, a few weeks after left Bell's palsy, developed a rumbling sound similar to a paper being crushed and a pulling sensation over her left ear, every time she blinked or protruded her jaw forward. Her Bell's palsy had taken place 6 months earlier. These ear sounds were very distressing to her and had been present for several months prior to her initial visit to the neurologist. She had intense pain and pressure behind her left ear that was greatly exacerbated during her menses. She reported enhanced hearing and noise intolerance over her left ear. She had experienced significant improvement of her facial muscle weakness by the time of her initial visit. Her past medical history was unremarkable. She denied previous episodes of Bell's palsy. She took no medication. There was no family history of neurological disorders. Her general physical examination was normal. On neurological examination she had mild facial asymmetry and left facial weakness. The left corner of the mouth contracted slightly with every blink. She had no pain talking, swallowing or chewing. There were no tremors of the palate. MRI of the brain was normal. Her blink reflex study, facial nerve latencies and mental nerve responses were normal. She exhibited large, polyphasic, motor units on EMG testing of her left facial muscles that discharged at high frequencies. There were fibrillations over the left mentalis, orbicularis oris and frontalis muscles. Motor unit potentials were detected over her left orbicularis oris muscle with every blink (synkinesis). Nerve conduction velocities (NCV) of her left median and ulnar nerves and median and ulnar sensory potentials were normal. All of her symptoms partially responded to the administration of carbamazepine 200 mg bid.
Discussion
Synkinesis is a common complication of complete peripheral facial paralysis. It is secondary to underlying axonotmesis and ipsilateral nerve degeneration (12). Although many firmly believe that they are caused by ephaptic transmission across damaged nerve fibres, others submit that enhanced central excitability of the facial nucleus forms the basis for the aberrant cross-innervation (12, 13). Patient 1's motor unit discharges triggered by sustained eye closure were tonic or continuous, rather than phasic, therefore more typical of dystonia, although she had no clinical signs of facial dystonia. Her cyclical facial dysesthesias can be explained on the basis of concomitant trigeminal nerve dysfunction appearing during her menses (‘pure’ sensory type in contradistinction to ‘motor’ dysesthesias arising from loss of muscle tone or underlying myokymia). Patient 2's myoclonic tinnitus (left ear rumble with jaw protrusion) was unusual and not typical of post-paralytic facial synkinesis, normally involving only facial nerve branches on the affected side. Instead, it was due to abnormally amplified sounds generated by the left lateral pterygoid muscle that extends in close proximity to the Eustachian tube (14, 15). The amplification of these sounds as the auditory tube snapped open was facilitated by residual weakness of the stapedius muscle, a facial nerve innervated muscle which role is to tense the tympanic membrane attenuating the incoming sounds (16). Conversely, her blinking-induced myoclonic tinnitus probably arose from abnormal stapedial muscle contractions based on either one of four mechanisms: (i) propagation of muscle contraction noise, (ii) vibration of the tympanic membrane, (iii) stimulation of the tympanic plexus, (iv) temporary variation of inner ear pressure or cochlear microphonic potential (17).
Although the ear is normally innervated by the second cervical dermatome (C2), the retroauricular pain experienced by these patients probably originated from cross-excitation of trigeminal pain fibres travelling in the facial nerve, via the auricular sensory branch, innervating the pinna and retroauricular area (18, 19). Of interest was the first patient's retroauricular pain appearing only during her menses, while in the second the pain was exacerbated during her menses. The circadian variability of cranial pain is well recognized (20). In women, for instance, a decrease in oestrogen levels during the menstrual period is linked to the increased incidence of migraine during menses (21). The pain reported by these patients perhaps could have been mediated by the locus ceruleus, a brain-stem nucleus implicated in the pathogenesis of headache, chronic pain and drug addiction and known to possess oestrogen receptors (22). An alternative explanation would be that their catamenial pain was mediated by female gonadal hormones acting on hyperexcitable trigeminal nerve fibres. The causal relationship between hormones and pain of trigeminal origin is supported by the study of Bereiter et al. (23). These investigators established that enlargement of individual trigeminal neurone receptive fields follows the systemic administration of oestrogens. On the other hand, a ‘rebound’ type of cranial pain due to hormonal withdrawal could be postulated, based on the participation of oestrogen concentrating opioid neurones, located at the ventromedial hypothalamus (24). Lastly, although hormonal influences in dystonia are recognized, no significant fluctuation on the synkinetic facial EMG abnormalities was detected in the first patient, when testing was performed at different times of her menstrual cycle (25).