Myokymia, a form of involuntary muscular movement, usually can be visualized on the skin as vermicular or continuous rippling movements.
The word myokymia was used first more than 100 years ago, when Schultze described continuous, slow, undulating muscular contractions in small muscles of hands and feet.[1] Kny used the term myoclonus fibrillaris multiplex to describe similar clinical manifestations.[2] For the past century, different authors applied the term myokymia to different involuntary muscular movements. Most of them showed electromyographic (EMG) evidence of spontaneous group discharges. This led to tremendous confusion in conceptually defining this particular clinical entity and its electrophysiologic features.
Eyelid myokymia is the most common type of facial myokymia.[3]
Facial myokymia has been reported to be associated with inflammatory demyelinating diseases,[4] brainstem neoplasms, Guillain-Barré syndrome, or other intramedullary pontine lesions. Facial myokymia also has been reported in patients with history of radiotherapy, with findings similar to those of more common brachial or lumbar radiation plexopathies.
The majority of patients with a history of radiation therapy have myokymic discharges detected within the field of radiation. Metastatic lesions generally are believed to be less likely to generate myokymia. The amount of radiation ranges widely, though myokymia rarely is reported with radiation doses less than 10 gray (Gy).
Electrodiagnostic findings are usually consistent with plexopathy. Other less common causes include acute or chronic inflammatory polyradiculoneuropathy[5] (with or without coexistent systemic vasculitis), ischemic or traumatic focal neuropathy, entrapment neuropathy, polyradiculopathy secondary to torticollis, syringomyelia, and chronic idiopathic plexopathy.
Transient myokymia, described in the calf or hand muscles, was reported after brief strenuous exercise, hypokalemia, hypomagnesemia, and increased caffeine intake. It usually resolves spontaneously over weeks to months.
Generalized myokymia is one of the cardinal features of Isaacs syndrome, which is a rare clinical entity with no known common etiologies.[6] Congenital and acquired forms are described.
The acquired form has been associated with neoplasms, thymoma, myasthenia gravis, lymphomas, and a variety of autoimmune nervous system disorders.
Spinal anesthesia and peripheral nerve block fail to abolish the myokymic discharges. Blocking the motor end plate transiently terminates the spontaneous activities. Evidence from muscle and nerve biopsies also favors a neurogenic origin.
Generalized myokymia also can be seen in patients with systemic illnesses (eg, thyrotoxicosis, uremia) and following binge consumption of alcohol, exposure to toxins, timber rattlesnake bite, gold therapy, and penicillamine therapy.
One case of myokymia as an initial and predominant manifestation of dermatomyositis has been reported.
The clinical phenomenon of myokymia is characterized by its classic quivering movement of the involved muscle without movement of the joint. Myokymia can be seen in muscles innervated by cranial or spinal nerves. The distribution can be either regional or generalized, depending on the etiology. Also, it can be seen transiently in healthy subjects after strenuous exercise.
The exact mechanism(s) of myokymia is not well understood. Myokymia of the facial muscles is believed to originate from the facial nucleus or from some contribution by a supranucleus process; however, the presence of myokymia in polyradiculopathy indicates the possibility of a more distal generator. Most authors agree that myokymia in other parts of the body is generated by distal motor axons, either by a primarily axonal process or by segmental demyelination with secondary axonal dysfunction. Some have postulated that transaxonal ephaptic excitation occurs peripherally after focal nerve damage leads to formation of an artificial synapse.
Myokymia is believed to be associated with generation of spontaneous activity, including myokymialike discharge in the dystrophic mouse whose nerve root axons have no Schwann-cell enwrapment. By this mechanism, spontaneous discharge could initiate volleys of activity or afferent fibers could directly stimulate efferent fibers in the vicinity of the lesion and produce a self-perpetuating reverberating circuit.
The central nervous system's electrotonic spread of discharge from rhythmic generators toward anterior horn cells also might play a role in generation of the spontaneous discharge. Each patient may have a different operating mechanism, depending on the particular areas involved and the different etiologies. The fact that patients with Isaacs syndrome respond dramatically to treatment of myokymia with phenytoin and/or carbamazepine[7] suggests a possible abnormality of the potassium channel in this particular entity.
Although myokymia can be seen in patients with different neurological and medical conditions and occasionally even in healthy subjects, it is a relatively rare clinical manifestation.
Most of the diseases associated with myokymia are not life threatening.
The prognosis is solely dependent upon the underlying etiologies.
Myokymia is considered benign when detected in patients after strenuous exercise.
Prognosis is related directly to the underlying etiology. Myokymia is reversible with successful treatment of the cause.[8]
Patients with myokymia may present with symptoms of pain, cramps, spasms, weakness, stiffness, or twitching.
Sensory symptoms are reported rarely, unless the underlying etiology(ies) includes sensory nerve involvement.
Typical myokymic discharges also can be seen in the EMGs of patients referred for totally unrelated complaints.
Findings of facial myokymia, segmental or focal myokymia in other areas of the body, and generalized myokymia are somewhat different in physical examination and in their potential etiologies; therefore, they are discussed separately.
Affected muscles show slow, undulating, fine movements on the surface of the skin due to activation of the most superficial muscle layers. Facial weakness can be present in the involved muscles.
EMG study shows typical myokymic discharges of spontaneous, rhythmic/semirhythmic bursts of normal-appearing potentials of 30–60 Hz. The bursts of each group of potentials are followed by a period of silence, with subsequent repetition of grouped discharges of identical potentials. The spontaneous activities are not altered by voluntary activation of the muscles.
These types of myokymia commonly are seen in the limbs or particular segmental level(s). Physical findings mostly are related to the underlying etiology(ies), which is usually asymptomatic and not a major concern of the patient.
EMG study shows myokymic discharges similar to those recorded in facial myokymia.
A triad of myokymia, muscular stiffness, and decreased deep tendon reflexes was first described by Isaacs in 1961; it also is called Isaacs syndrome.[9, 10, 11, 12]
The myotonic discharge recorded by EMG ceases upon relaxation of the muscle, while spontaneous grouped discharges of myokymia persist for some time, well above the abnormal pattern that was present before the voluntary contraction.
Complete blood count, chemistry, creatine kinase, thyroid testing group, sedimentation rate, Lyme titer, Venereal Disease Research Laboratory (VDRL) test, and rheumatology screening are the basic laboratory tests for all patients with clinical myokymia. Serum alcohol level and toxic screen are recommended for acute onset of generalized myokymia.
Neuroimaging studies with CT scan or MRI usually are performed for certain regions after careful examination and in cases in which electrodiagnostic studies have localized a lesion to a particular area. For example, if facial myokymia is confirmed, MRI study of the brain with special attention to posterior fossa is ordered to search for an anatomic lesion. Imaging studies are not otherwise necessary for establishing the diagnosis of myokymia.
Muscle ultrasound has proven effective in detecting myokymia, especially in cases like radiation-induced brachial plexopathy. Ultrasound can reveal characteristic semirhythmic contractions, serving as a noninvasive diagnostic tool.[13]
Nerve conduction velocity (NCV) and EMG studies are necessary to qualify and quantify neurogenic/myogenic dysfunction.
Lumbar puncture with examination of cerebrospinal fluid (CSF) usually is performed for patients with documented acute or chronic polyradiculoneuropathy, central nervous system demyelinating disorder, or other suspected inflammatory, infectious, or neoplastic processes.
Treatment of myokymia is focused largely on the underlying etiology. Most patients with facial or focal limb myokymia are not particularly disturbed by the myokymia itself. The accompanying symptoms of the particular neurological or medical conditions are the major concern to patients and their caretakers.
No particular activity restriction is imposed on a patient with myokymia. For patients with stiffness and painful cramps, conditioning of muscles by range of motion and isometric exercise is helpful.
Phenytoin and carbamazepine have been proven to be effective in treating patients with generalized myokymia, specifically patients with continuous muscle fiber activity described by Isaacs syndrome. High therapeutic drug levels usually are required to reach satisfactory control of symptoms. EMG can objectively document the disappearance of myokymic discharges. In some cases, combining anticonvulsants with immunotherapies, such as plasma exchange and high-dose steroids, has yielded improved symptom control.[14]
Other newer-generation anticonvulsant medications with mechanisms of action modulating sodium and potassium channels can also be tried with caution. Monitoring of potential adverse effects of phenytoin and carbamazepine and precautions for these drugs are no different from when they are used to treat epilepsy. Medications such as benzodiazepines have been tried with no consistent benefit.
Clinical Context: Has promising results in patients with Isaacs syndrome. Relieves cramps and pain of involved muscles. EMG can document objective resolution of myokymic discharges. Mechanism of action possibly related to its effect on sodium channel.
Dosage adjusted according to blood level. Target level should be at high therapeutic range.
Clinical Context: Has promising results in patients with Isaacs syndrome. Relieves cramps and pain of involved muscles. EMG can document objective resolution of myokymic discharges. Mechanism of action possibly related to its effect on sodium channel.
Dosage adjusted according to blood level. Target level should be at high therapeutic range.