Myokymia consists of involuntary, fine, continuous, undulating contractions that spread across the affected striated muscle. It is characterized electrophysiologically by rhythmic or semi-rhythmic bursts of a single motor unit discharging several times per second at a rate of 3 to 8 Hz. These myokymic discharges are non-synchronous in different muscles or even in the same muscle, with intervals of 100 to 200 milliseconds separating individual bursts (1-3). The spontaneous discharges are not initiated by voluntary movement, although they may increase with such activity (2).
Facial myokymia affects one or more muscles of the face. The most common type involves the orbicularis oculi and is often called eyelid myokymia. This condition tends to be unilateral, affecting the lower eyelid. It is often transient, occurring in normal individuals during times of severe fatigue, stress, physical exertion, or with excessive caffeine intake (4). The myokymia usually lasts for only a few days, although occasionally it persists for several weeks or even a few months before resolving, with the spasms being intermittent throughout the day, lasting up to several hours at a time (5). In rare cases, the eyelid myokymia gradually spreads over several months to affect additional muscles on one or both sides of the face, producing benign essential blepharospasm, Meige syndrome, hemifacial spasm, or, rarely, spastic-paretic facial contracture (3).
Unlike eyelid myokymia, facial myokymia primarily affecting the lower face or cheek is often caused most often by intrinsic or extrinsic lesions or conditions that damage the facial nerve nucleus in the pons. Intrinsic conditions that have been include multiple sclerosis, brainstem neoplasms (glioma, metastatic disease) or vascular lesions (cavernous angiomas), tuberculomas, syringobulbia, Guillain-Barré syndrome, spinocerebellar ataxia type 3 (Machado-Joseph disease), cysticercosis, and autosomal-dominant striatonigral degeneration. Extrinsic processes include obstructive hydrocephalus, subarachnoid hemorrhage, basilar invagination, and extra-axial neoplasms that compress the brainstem (3). To verify that myokymia limited to the eyelid is unlike facial myokymia in being unassociated with more serious neurologic conditions, we undertook a follow-up study of such patients. We are unaware of any comparable study.
After approval by the Institutional Review Board of the Johns Hopkins University School of Medicine, we identified all patients seen in the Neuro-Ophthalmology Unit at the Wilmer Eye Institute between 1982 and 2003 and coded as having eyelid myokymia. The records of all patients with this diagnosis were reviewed to identify patients whose myokymia had persisted for at least 3 months on a daily basis. Fifteen patients met this criterion. The charts of these 15 patients were then used to collect data on demographics, symptom duration, associated symptoms, comorbid conditions, clinical signs, neuroimaging studies, treatment, and outcome. An attempt was then made to contact all patients to determine their clinical status. In all 15 cases, follow-up of at least 12 months (range, 12 months to 20 years) after initial assessment in the Neuro-Ophthalmology Unit was available.
Ten patients were female and five were male; all were white. The average age at onset of symptoms was 37.3 years. The right lid was affected in eight cases, the left lid in seven. The lower lid was involved in 14 patients, and the upper lid in one. In all cases, the condition began as episodic twitching of the eyelid lasting several minutes at a time, occurring once or twice weekly. Within 3 to 6 months after onset, the symptoms progressed to daily episodes of spasms lasting several minutes each. The duration of symptoms at the time of initial examination ranged from 2.5 months to 20 years. Seven patients were smokers, eight admitted to moderate alcohol intake, and nine had moderate caffeine intake (Table 1).
Over the course of follow-up, one patient had ipsilateral hemifacial spasm 1 year after the onset of eyelid myokymia symptoms. Another patient had clinically definite multiple sclerosis diagnosed after an episode of cerebellar ataxia followed by optic neuritis. Her myokymia began 4 months before the diagnosis of clinically definite multiple sclerosis and resolved within 6 months. Neuroimaging at that time of onset of the myokymia showed no lesions in the brainstem or along the course of the seventh cranial nerve. The patient subsequently developed chronic progressive multiple sclerosis, but with no recurrence of eyelid myokymia. A third patient with a previous history of transient ischemic attacks characterized by transient diplopia and slurred speech had Alzheimer disease and severe dementia diagnosed 11 years after the onset of myokymia symptoms.
Thirteen (86.7%) of the 15 patients underwent brain neuroimaging. Three had computed tomographic scans and 10 had magnetic resonance imaging scans. In no patient did neuroimaging reveal a mass or other pathologic process affecting the brainstem or the course of the peripheral facial nerve.
The eyelid myokymia resolved spontaneously within 6 months of symptom onset in four patients (in two after the resolution of significant stressors). Among the remaining 11 patients, eight were treated with botulinum toxin (Botox, Allergan, Inc., Irvine, CA) injection into the affected eyelid. Two of these patients had resolution of the myokymia after a single injection, five patients required repeat annual or biannual treatments, and one patient had no improvement in myokymia after an initial botulinum toxin injection and did not return for subsequent treatment.
Isolated eyelid myokymia, usually affecting the lower lid, tends to be a transient unilateral condition. However, in some cases, the condition becomes chronic. Although previous reports have suggested that chronic eyelid myokymia can progress to involve the lower face and that myokymia involving the lower face is often a manifestation of a more serious underlying condition affecting the caudal brainstem (3,6-8), our experience with persistent myokymia limited to the eyelid suggests that it is benign. Among our 15 patients, 12 (80%) had no evidence of any underlying neurologic disorder during a follow-up period that ranged from 12 to 240 months, with a mean of 91 months. Of the three patients who did have other findings, only one had a related condition, ipsilateral hemifacial spasm. In the patient in whom clinically definite multiple sclerosis developed, there was no definite evidence by neuroimaging that the eyelid myokymia was related, nor did the myokymia symptoms lead to the diagnosis. One patient had Alzheimer disease but there was no temporal association with her eyelid myokymia.
Thus, although patients with isolated, persistent eyelid myokymia routinely undergo neuroimaging studies to rule out an intrinsic or extrinsic process affecting the pons, the performance of such studies is unwarranted because of its very low yield.
In facial myokymia, these imaging studies are undertaken to discover lesions that may be supranuclear, perinuclear, nuclear, or infranuclear. In some cases, there is a lesion in the brainstem rostral to the facial nerve nucleus leading to supranuclear disinhibition (8). In other cases, loss of perinuclear interneurons synapsing on the facial nerve nucleus results in functional deafferentation (8). Still other cases are caused by damage to peripheral nerve fibers, as after radiation therapy, in which there is segmental demyelination of peripheral facial nerve fibers innervating the orbicularis oculi (as evidenced by transcranial magnetic stimulation studies) (9) or in which antibodies to voltagegated potassium channels (10) are present. Ephaptic transmission with 'cross-talk' of fibers or ectopic excitation may occur in neighboring branches of the facial nerve. The result is hyperexcitability of facial nerve fibers.
The cause of chronic, isolated eyelid myokymia is less clear. The chronic, localized nature of the process without progression to involve other ipsilateral facial muscle groups suggests the lesion is peripheral. However, no electrophysiologic studies have yet been performed on this particular subset of patients. Psychosocial factors, such as fatigue, lack of sleep, physical exertion, stress, smoking, alcohol, or caffeine may play a role in the development and persistence of the process. More than half of our patients admitted to one or more of the latter three habits, but in no case could we establish a temporal relationship between the onset of symptoms and these habits. It is noteworthy that in two cases, the myokymia did improve within 6 months after relief of work-related stress and anxiety.
We believe that most patients with isolated eyelid myokymia should be managed conservatively, with reassurance, rest, and elimination of or reduction in possible risk factors, such as smoking, alcohol ingestion, and caffeine intake. If the myokymia persists for more than 3 months and is bothersome to the patient, further intervention may be warranted. Although limited surgical myectomy of the affected pretarsal and preseptal orbicularis oculi has been shown to be of benefit and, in some cases, curative (5), palliative injections of botulinum toxin are also quite successful and less invasive than surgery (11). Interestingly, two of our patients had complete resolution of their myokymia with a single injection, as has been reported previously in cases of eyelid and facial myokymia (5,11,12). Whether this outcome was a direct consequence of the treatment, or simply coincident with the natural history of the condition, is impossible to determine.
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