Myokymia in the course of Bell's palsy. An electromyographic study

Facial myokymia has been described in association with many morbid conditions, most frequently multiple sclerosis (MS) and brainstem tumors (BST). Very few reports deal with myokymia in the course of Bell's palsy, despite high frequency of the disease. A series of 88 consecutive patients with Bell's palsy is presented, in which serial EMG controls were performed in the initial phases of facial palsy. Twenty three showed myokymic activity detected by EMG, while clinically evident myokymia could be observed only in 8. EMG features did not reveal any peculiarity as compared with myokymic discharges reported in other pathological situations. Considering the high incidence of myokymic activity reported in the course of Bell's palsy, it is the authors' opinion that an occasional finding of myokymia, both clinically evident or detected by EMG, should not necessarily lead one to suspect serious aetiologies.     

Nuclear magnetic resonance imaging in a case of facial myokymia with multiple sclerosis

A 59-year-old female of facial myokymia with multiple sclerosis was reported. In this case, facial myokymia appeared at the same time as the first attack of multiple sclerosis, in association with paroxysmal pain and desesthesia of the neck, painful tonic seizures of the right upper and lower extremities and cervical transverse myelopathy. The facial myokymia consisted of grossly visible, continuous, fine and worm-like movement, which often began in the area of the left orbicularis oculi and spread to the other facial muscles on one side. Electromyographic studies revealed grouping of motor units and continuous spontaneous rhythmic discharges in the left orbicularis oris suggesting facial myokymia, but there were no abnormalities on voluntary contraction. Sometimes doublet or multiplet patterns occurred while at other times the bursts were of single motor potential. The respective frequencies were 3-4/sec and 40-50/sec. There was no evidence of fibrillation. The facial myokymia disappeared after 4-8 weeks of administration of prednisolone and did not recur. In the remission stage after disappearance of the facial myokymia, nuclear magnetic resonance (NMR) imaging by the inversion recovery method demonstrated low intensity demyelinated plaque in the left lateral tegmentum of the inferior pons, which was responsible for the facial myokymia, but X-ray computed tomography revealed no pathological findings. The demyelinated plaque demonstrated by NMR imaging seemed to be located in the infranuclear area of the facial nerve nucleus and to involve the intramedurally root.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neuromyotonia masquerading as tetanus

Neuromyotonia, or Isaac’s syndrome, is a rare neuromuscular disorder of peripheral nerve hyperexcitability characterized by muscle stiffness, muscle hypertrophy, pseudomyotonia, myokymia and electromyographic evidence of myokymic or neuromyotonic discharges. A young boy with neuromyotonia is presented who was diagnosed with tetanus for severe muscle spasms, trismus and ophisthotonos. We discuss differentiation of neuromyotonia from tetanus and other disorders with similar features on clinical and electrophysiological examination.     

Calcium effect on generation and amplification of myokymic discharges

Maneuvers designed to manipulate ionized calcium (Ca++) were carried out in two patients with inflammatory polyradiculoneuropathy and myokymia. Increased clinical myokymia and myokymic burst amplification occurred when ionized Ca++ was lowered by plasma exchange or hyperventilation. Increasing ionized Ca++ (by intravenous infusion of CaCl2) decreased the myokymia. These findings indicate that myokymic discharges are altered by changes in serum ionized Ca++ and effects on axonal excitability.     

A case of myokymia-hyperhidrosis syndrome with muscle involvement

The present report deals with an unique case of myokymia-hyperhidrosis syndrome. A 46-year-old man developed generalized relatively slow, undulating movement of the muscles, excessive sweating, muscle cramps and easy fatigability since three years ago. On admission, he had generalized myokymia, abnormal movements consisting of slow, undulating and worm-like muscular contractions. There was no muscle atrophy or weakness, or sensory deficits. Deep tendon reflexes were diminished and no Babinski sign or other pathological reflexes were present. Muscle tone was in normal range. Neither fasciculation nor myotonia was found. Laboratory examinations revealed elevation of BMR with normal thyroid function. The value of anti-Ach receptor antibody was below 0.6nmol/l. EMG recordings showed (1) continuous spontaneous repetitive discharges of NMU at a frequency of 30-50Hz, with duration of 1-2 seconds and amplitude of about 1 mV, were demonstrated at rest and the findings were consistent with myokymia, (2) waxing phenomenon was observed on repetitive peripheral nerve stimuli, which didn't improve by the tension test, and (3) high amplitude, long duration and polyphasic NMU, a sign of denervation, were observed on voluntary contraction. Muscle biopsy specimens from the left quadriceps showed a number of internal nuclei. On electron microscopy, clustered mitochondria and filamentous bodies were very often found in subsarcolemma. From these observations, damage to peripheral nerves, neuromuscular junctions and muscles may be responsible for the generalized myokymia in our patient.     

The electromyogram in facial myokymia and hemifacial spasm

Electromyographic findings in 5 patients with facial myokymia due to multiple sclerosis and in 10 patients with hemifacial spasm are described and compared.Many of the spontaneously discharging motor units in myokymia are not under voluntary control.In hemifacial spasm the high frequencies of discharge reached in blink bursts are similar to those recorded during normal involuntary blinking.The possible sites of origin of the discharges are briefly discussed.     

Neuromyotonia in mice with hereditary myelinopathies

The purpose of this study was to further characterize neuromyotonia in mice with deletions and point mutations of myelin protein genes. Clinical observation showed irregular stretching of the hindlimbs, tremor and generalized myokymia in mice with targeted deletions of the genes encoding myelin protein zero (P0-/-) or peripheral myelin protein 22 (Pmp22-/-), and Trembler mice, which carry a point mutation of Pmp22. By electromyography (EMG), we found irregular high-frequency bursts of spontaneous motor unit activity and rhythmic doublet or multiplet discharges of motor units in these mouse models of human hereditary neuropathies. The EMG signs are typical for neuromyotonia and myokymia, respectively. The activity persisted after a proximal nerve section in many cases, localizing the generator to the peripheral nerve or the muscle. We now show that blocking neuromuscular transmission with suxamethonium abolished the spontaneous activity, ruling out a muscle origin. Phenytoin ameliorated the motor behavior. Taken together, our study shows that neuromyotonia develops in different mouse models of hereditary myelinopathies. This indicates that spontaneous motor unit activity may underlie neuromyotonia, which is occasionally observed in Charcot-Marie-Tooth disease. These animal models will be useful to study the pathogenesis of neuromyotonia.     

Isaacs syndrome: A review

Isaacs syndrome is a peripheral nerve hyperexcitability (PNH) syndrome that presents as continuous motor activity. Clinical findings include cramps, fasciculations, and myokymia. Electrodiagnosis plays a key role in diagnosis by demonstrating after‐discharges on nerve conduction studies, and fasciculation potentials, myokymic discharges, neuromyotonic discharges, and other types of abnormal spontaneous activity on needle examination. Etiopathogenesis involves the interaction of genetic, autoimmune, and paraneoplastic factors, which requires a broad‐ranging evaluation for underlying causes. Initial treatment is symptomatic, but immune therapy is often needed and can be effective. The purpose of this review is to describe the syndrome and its pathogenesis, assist the reader in evaluating patients with suspected Isaacs syndrome and distinguishing it from other disorders of PNH, and suggest an approach to management, including both symptomatic and immunomodulating therapy. Muscle Nerve 52 : 5–12, 2015     

Post-radiation branchial plexopathy. Persistent conduction block. Myokymic discharges and cramps

The distinction between radiation and tumor brachial plexopathy may be difficult. The electrophysiological recording of myokymic discharges, frequently present in the former but rare in the latter type of plexopathy, can be helpful for the diagnosis. However, the pathophysiology and the site of origin of these discharges remain unclear. We describe a patient presenting with radiation brachial plexopathy, clinical myokymia, cramps and pain. In this patient, the myokymia--due to abundant myokymic discharges--and the cramps, were related to the existence of persistent conduction block of several years duration. Several findings suggest that the myokymic discharges were generated on blocked axons: voluntary activity did not influence their occurrence nor modify their course; the motor unit potentials involved in the discharges were not evoked by stimulation proximal to the site of the conduction block, whereas the stimulation distal to this site could evoke, modify the rhythm, or interrupt the course of the discharges; the latency of these evoked responses indicated that the site of reflection was proximal on the axon, and likely coincided with that of the conduction block. Recent observations (Roth and Magistris, 1987b) indicated that myokymia, produced by numerous single or grouped fasciculations generated on axon terminals, may be related to persistent conduction blocks of various etiologies. The present case demonstrates that myokymia provoked by myokymic discharges may as well be related to persistent conduction block. The reason why these blocks are accompanied by fasciculations in some situations and by myokymic discharges in others remains an unsolved question. The cramps observed in this patient were also of interest as they occurred in the muscle territory of blocked axons and were provoked by passive muscle shortening. Their origin, distal to the conduction block, is unknown. Finally, a neurolysis did not prevent the progressive transformation of conduction block into axonotmesis.     

Post-irradiation myokymia and neuromyotonia in unilateral tongue and mentalis muscles: report of a case

We report a 52-year-old man with slowly progressive dysarthria and dysphagia for about 11 years after radiation therapy of nasopharyngeal carcinoma. Neurological examination revealed atrophy and myokymia on the left side of the tongue and in the left mentalis muscles. Electrical discharges of myokymia and neuromyotonia were also observed in the aforementioned muscles, suggesting increased motor axonal membrane excitability involving the left hypoglossal nerve and the marginal mendibular branch of the left facial nerve. Magnetic resonance imaging of the brain did not show any evidence of tumor recurrence, indicating that irradiation probably plays an important role in pathogenesis. Focal myokymia with concomitant neuromyotonia in unilateral tongue and mentalis muscles could be an unusual delayed manifestation after radiation therapy.     

Electrophysiological study on limb myokymia in three women.

Physiological studies on three women with limb myokymia were carried out. The patients had diabetic neuropathy, neuromyotonia, and autonomic polyneuropathy, respectively. The EMG discharge pattern, coincident with myokymia, in a patient with myokymia and neuromyotonia differed from those with myokymia without neuromyotonia. In only the first patient did the electrical stimulation of nerves evoke "late repetitive response" (LRR), which resembled the wave forms of the myokymic discharge. Epidural and peripheral nerve blocks abolished myokymia in the first and second cases, but peripheral nerve block was without effect in the third patient. These findings indicate that myokymia originates in multiple sites of alpha motor neurons and that the pathophysiology may vary.     

Adult GM2 gangliosidosis: improvement of ataxia with GABAergic drugs

The authors present a case of adult GM2 gangliosidosis, B1 enzymatic type. The main clinical features found were cerebellar ataxia, proximal lower limb weakness and myokymia. The neurological examination, and the biochemical, electrophysiologic and imaging studies are all described. Decreased activity of the enzyme beta-hexosaminidase A in the metabolism of the sulfate substrate 4-MU-NAGS was found in serum. Global cerebellar atrophy was observed in a cranial nuclear magnetic resonance. The electrophysiologic study showed continuous spontaneous activity integrated by myokymia and neuromyotonic discharges in addition to signs of acute and chronic denervation. Disappearance of the myokymia and improvement in the ataxia were attained with the use of the GABAergic drugs gabapentin and tiagabine. The authors try to explain the clinical improvement obtained with the drugs by relating their mechanisms of action to the central nervous system neurotransmitter alterations proposed for this disease.     

Hereditary myokymia and paroxysmal ataxia linked to chromosome 12 is responsive to acetazolamide.

A sixth family with autosomal dominantly inherited myokymia and paroxysmal ataxia is described. The syndrome in this family is linked to the recently discovered locus for inherited myokymia and paroxysmal ataxia on the human chromosome 12p, and a missense mutation is shown in the KCNA1 gene. The attacks of ataxia in this family compare well with those of previously described families and similarly are precipitated by kinesigenic stimuli, exertion, and startle. Responsiveness of these attacks to low dose acetazolamide is confirmed, but some loss of efficacy occurs with prolonged treatment, and side effects are notable. Although not all affected family members showed myokymia on clinical examination, electromyography invariably showed myokymic discharges, in one patient only after a short provocation with regional ischaemia. One affected family member also had attacks of paroxysmal kinesigenic choreoathetosis, responsive to carbamazepine.     

Trigeminal myokymia in a young girl

Myokymia results from complex bursts of repetitive discharges of a motor unit typically attributable to a demyelinating condition. We report a 12-year-old girl with unilateral trigeminal myokymia who presented with involuntary jaw movements. Electromyography demonstrated unilateral rhythmic myokymic discharges in the left masseter and temporalis muscles at a rate of 3.5 Hz. Abnormal jaw movements spontaneously resolved over 8 months without treatment or residual deficits. The pathophysiology of myokymic discharges is discussed.     

Facial myokymia with polyradiculoneuropathy

Two patients had bilateral facial myokymia in association with polyradiculoneuropathy. Characteristic electromyographic findings allow polyradiculoneuropathy to be differentiated from other causes of facial movements, and support the possibility that extraaxial facial nerve involvement is another cause of facial myokymia.     

Hereditary myokymia and periodic ataxia.

A kindred in which at least 11 individuals in 3 consecutive generations have continuous muscle movement, i.e., myokymia, and periodic ataxia, has been studied. Three patients, a 24-year-old woman, her 4-year-old son and her 27-year-old sister, have been studied in detail. The disorder is inherited as an autosomal-dominant trait and presents in early childhood with attacks of ataxia of 1-2 min in duration, with associated jerking movements of the head, arms and legs. Attacks are provoked by abrupt postural change, emotional stimulus, and caloric-vestibular stimulation. At the age of 12 years approximately, facial and extremity myokymia appears. Physical findings include large calves, normal muscle strength and widespread myokymia of face, hands, arms and legs with a hand posture resembling carpopedal spasm. EMG studies at rest showed continuous spontaneous activity of otherwise normal motor units. Nerve conduction velocities were normal. Gastrocnemius biopsy in 2 patients showed fiber type grouping and small angular fibers, and was consistent with denervation. Histographic analysis of the biopsies demonstrated enlargement of both fiber types, particularly of Type I fibers. These findings are consistent with chronic denervation and an abnormality of motor neuron population or firing. The myokymia described here is of interest not only because of its genetic association with a movement disorder, but also because the muscle findings support a peripheral basis for the muscle movements.     

Timber rattlesnake venom-induced myokymia: evidence for peripheral nerve origin

Facial and limb myokymia occurred in four consecutive cases of timber rattlesnake envenomation and represents the "fasciculations" frequently reported in this entity. The facial myokymia disappears within hours of antivenin therapy and the limb myokymia by increasing serum ionized calcium. These observations suggest that the action of the venom is a biochemical one, increasing peripheral nerve excitability.     

The stiff-man syndrome and related disorders

The stiff-man syndrome (SMS) is characterised by rigidity and spasm of predominantly axial and proximal limb muscles. The cause of the condition is unknown but the finding of antibodies to glutamic acid decarboxylase (GAD) in approximately 60% of patients has suggested an autoimmune basis. Pathological findings are limited to a small number of cases which are reviewed in this paper. In some, evidence of an inflammatory aetiology has been found, and there appears to be overlap with progressive encephalomyelitis with rigidity (PER) which may present with a similar clinical picture. The spontaneous muscle activity in SMS and PER is of central origin, related to release of polysynaptic spinal and brainstem reflexes. The SMS is readily distinguished from the continuous muscle activity, spasm and cramps of Isaac's syndrome and neuromyotonia which originate in the peripheral nervous system. Fasciculations, myokymia, myotonia and complex repetitive discharges are characteristic of these peripheral neuromuscular disorders.     

Delayed radiation-induced bulbar palsy mimicking ALS

We describe a patient presenting with progressive bulbar dysfunction and spasticity that clinically mimicked amyotrophic lateral sclerosis (ALS). Electromyography, however, showed no evidence of denervation and revealed a rare combination of peripheral and central myokymia. We feel that this pattern of myokymia represented a marker of neural injury from remote radiation therapy. Nervous system disorders resulting from therapeutic radiation are described, and potential pathophysiologic mechanisms underlying myokymia are discussed.     

Calcium and myokymia of brainstem origin

In five patients with Guillain-Barré syndrome, clinical myokymia increased and myokymic burst amplification occurred when ionized Ca++ was lowered by hyperventilation. Myokymia decreased when ionized Ca++ was increased after IV infusion of CaCl2. These responses were absent or diminished in the four patients with myokymia due to brainstem lesions, suggesting that the blood-brain barrier impedes the effects of altered serum ionized Ca++ on axonal excitability. Altering serum Ca++ can distinguish peripheral and central myokymia.