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Hemifacial spasm typically consists of unilateral involuntary spasms of the mimic muscles innervated by either facial nerve. There is some controversy whether mechanical irritation of the facial nerve entry zone by vessels in the cerebellopontine angle or hyperexcitability of the facial nerve nucleus is the main cause of this problem.1 2 To our knowledge, only two cases of bilateral hemifacial spasm have been described in some clinical detail but without electrophysiological recordings.3 4 The mechanism underlying the bilateral occurrence of spasms has not been investigated so far: either hyperexcitability of a facial nerve nucleus spreading to the contralateral side or independent mechanical irritation of both nerves might be involved. We report a patient with predominantly left sided spasms, electrophysiological diagnosis of bilateral facial spasm, the clinical course after surgical treatment according to MR evidence of elongated vertebral and basilar arteries, and implications of electrophysiological recordings on the pathogenesis of bilateral hemifacial spasm.
This 60 year old male patient presented with a history of gradually increasing left eye twitching over the past few years. He did not notice involvement of other facial muscles or of associated symptoms such as hearing deficits, vertigo, or headache. Visual inspection showed frequent clonic involuntary synchronous contractions of his left orbicularis oculi and left orbicularis oris muscles. On voluntary contraction of the orbicularis oculi muscle, there was some synkinesis of the left orbicularis oris muscle and vice versa. There was no weakness of facial muscles or other neurological deficit. Four channel surface EMG recording from facial muscles was performed to ascertain the suspected diagnosis of left hemifacial spasm. Recordings gave evidence of irregular and asynchronous spasms of left and right facial muscles with higher frequency, amplitude, and longer duration on the symptomatic left side (fig 1A). Blink reflex recordings with stimulation of either supraorbital nerve showed bilateral R2 components also involving the orbicularis oris muscles of both sides (fig 1B); latencies of R1 and R2 components were in the normal range. Magnetic resonance imaging showed a grossly distended vertebral and basilary artery approaching first the right cerebellopontine angle and later in its course also the left cerebellopontine angle before taking its normal median position in its rostral segment (fig 2). This extraordinary course suggested a possible mechanical irritation of both facial nerves.
The patient thus had a neurovascular decompression on the symptomatic left side. During surgery, close contact of the basilary artery with nerve entry zones of the left facial and vestibulocochlear nerve was found. After interposition of a piece of ivalon sponge, spasms of the left facial muscles disappeared almost completely leaving a slight left facial nerve paresis which cleared completely over the next months without functional deficit. There was a partial hearing loss on the operated side. Electrophysiological control recordings 4 months after surgery showed a reduction of the amplitude of compound muscle action potentials recorded from the left orbicularis oculi muscle. There was also a loss of facial synkinesis on the operated side, whereas spontaneous spasms and synkineses of the right facial muscles remained unchanged or even slightly increased (fig 1A). Right sided spasms have become more prominent also during clinical investigation; they have, however, so far not bothered the patient enough to warrant an additional contralateral operation.
Bilateral twitching of facial muscles most commonly occurs in blepharospasm; this focal dystonia may occasionally mainly present by contractions of the orbicularis oculi muscle of only one side as experienced by our patient. Even more so, in patients with bilateral hemifacial spasm a dystonic aetiology may be erroneously attributed and lead to unsuccessful treatment.3 Needle EMG recordings can be helpful in discriminating these diseases by showing unphysiologically high frequent discharges of motor units in hemifacial spasm.5 With surface electrodes, simultaneous electrophysiological recording from facial muscles of both sides can differentiate this disorder from the rare bilateral hemifacial spasm by showing synchronous twitching of the muscles innervated by each facial nerve but asynchrony of muscle twitching between right and left facial muscles. In normal subjects and on the unaffected side of patients with unilateral hemifacial spasm R2 components of the electrical blink reflex are restricted to both orbicularis oculi muscles, but additional facial muscles are usually involved in patients with hemifacial spasm. This synkinesis of other muscles, which was found in this patient bilaterally, could be due to ephaptic transmission at the nerve entry zone or to facial nerve nucleus hyperexcitability; the immediate postoperative disappearance of synkinesis and abnormal R2 spread found in this case would thus be compatible with either suppression of ephaptic transmission at the nerve entry root or reduction of secondary facial nerve nucleus hyperexcitability. Both the asynchrony of spontaneous muscle bursts and the persistence or even increase of spasms on the less affected side after contralateral successful surgery in our case suggest independent trigger mechanisms on both sides most probably due to bilateral nerve entry zone irritation by aberrant vessels. Even with irritation of the nerve entry root being the probable primary cause, hyperexcitability of brain stem nuclei may also play a part; the reduced contralateral R2 component of the orbicularis oris muscle of the side contralateral to surgery (fig 1B) might be due to a loss of facilitatory effect of the operated side on the generation of this response.
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