Limb Myokymia in Guillain-Barré Syndrome
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.279682
Source of Support: None, Conflict of Interest: None
Myokymia is fine, persistent quivering, or rippling of muscles. Myokymia occurs in variety of disease states. The reason for the development of myokymia is biochemical perturbation in the microenvironment of the nerve due to demyelination, a toxin (such as rattle snake venom or gold salts), edema, or a decrease in ionized calcium concentrations. Myokymia may be generalized or focal/segmental. Focal myokymia is more common. Focal myokymia involving facial muscles is noted in intramedullary brainstem lesions such as multiple sclerosis, pontine glioma, posterior fossa tumor, brainstem vascular diseases, occasionally poliomyelitis affecting facial nucleus, and in extramedullary or extra-axial lesions like Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyradiculoneuropathy, whereas focal myokymia involving limb muscles can occur with radiation damage to a nerve or plexus and rarely in GBS.
Although focal myokymia involving facial muscles had been reported often in GBS, limb myokymia had been reported rarely. We report a patient who was admitted in our institute with GBS, who manifested myokymia in both lower limbs.
A 54-year-old man was admitted for difficulty in swallowing and walking of an eight-day duration. He was treated for a viral prodrome about four weeks earlier, which lasted for six days. Two weeks later, the patient noticed difficulty in swallowing with slurring of speech, difficulty in getting up, walking, and moving both upper limbs. Initially, he was attended by a general physician and eight days later referred to our hospital as the symptoms did not improve. There were no sensory or bladder disturbances in the history. He was not a hypertensive or diabetic. His personal history revealed that he used to consume alcohol twice per week. Otherwise, his past medical history was unremarkable.
When received the patient in intensive medical care unit, his blood pressure was 140/80 mm Hg, pulse rate was 90/min, arterial oxygen saturation was 97% with respiratory rate of 16/min. His sensorium was intact. Pupils were bilaterally 2.5 mm in size with retained light reflex. Examination for extraocular movement showed no ophthalmoplegia or nystagmus. Bilateral asymmetrical facial weakness was noticed with more weakness in right side. Dysarthria was present as well. Bilateral palatal movements were impaired. Minimal neck flexor weakness was noticed. The spinomotor system examination revealed quadriplegia with no stiffness in muscles. Power in both upper limbs was proximally 3/5 and distally 4/5 and in both lowers limbs proximally 2/5 and distally 3/5. Deep tendon reflexes were all absent. Plantar reflex showed bilateral flexor response. Sensory system examination for light touch, vibration, pain, and temperature were normal. These clinical features suggested the diagnosis of acute GBS.
In addition, examination showed diffuse and wide spread myokymia over both lower limbs in calf and thigh muscles [Videos 1-3], which persisted during sleep. In addition, there were fasciculations noticed over upper limbs and trunk. Initially, myokymia was also noticed in lower half of face, which disappeared after two days.
The investigations showed the following results - complete hemogram, liver function tests, metabolic parameters, and serum electrolytes were in normal limits. (serum K+ was 4.4 meq/l, calcium was 10.0 mg%). Serology for HIV, HCV, and HBsAg were negative. ECG showed normal sinus rhythm with rate of 100/min and T inversion noted in V1-V6 with minimal ST depression in V3 and V4 [Figure 1] and [Figure 2].
Motor and sensory nerve conduction studies were done (Results are given in [Table 1] and [Table 2]). Motor nerve conduction showed prolonged distal latency, reduced conduction velocity, and minimally reduced compound muscle action potential (CMAP) amplitude. Sensory nerve conduction showed normal latency with normal sensory nerve action potential amplitude and reduced conduction velocity. F-waves could not be evoked in both upper and lower limbs. These features were consistent with predominant demyelinating polyradiculoneuropathy. Bilateral facial nerves showed reduced CMAP amplitude.
Needle electromyogram done in gastrocnemius and quadriceps of both lower limbs showed spontaneous, repetitive, irregular, grouped discharges of motor units suggestive of myokymia [Figure 3], [Figure 4], [Figure 5], [Figure 6] and Videos 4-6]. The electrophysiological characteristics of myokymic discharges were as follows: burst duration was 80-130 ms, intra-burst spike frequency was 80-120 Hz, inter-burst interval was 120-200 ms, spikes per burst was 4-18, and burst amplitude was 250-550 μV (Sweep speed used was 100 msec).
Magnetic resonance imaging of the brain showed T2/FLAIR bilateral subcortical and periventricular hyperintense signals suggestive of mild leukoariasis [Figure 7] and [Figure 8]. Otherwise no relevant abnormalities were seen.
The patient was diagnosed as a case of acute GBS with respiratory adequacy. Treatment was initiated with nasogastric tube feeding, parenteral fluids, methyl prednisolone injection, and advised continuous vital signs monitoring with special importance to respiratory function, supportive care, and physiotherapy. As respiratory rate and arterial oxygen saturation were fair, endotracheal intubation was not done.
There was no further progression of the disease. Myokymia in limbs started reducing after 1 week of admission and completely disappeared after 2 weeks. The patient showed satisfactory recovery and power in skeletal muscles improved to 4+/5 in upper limbs and 4/5 in lower limbs at 3 weeks of admission, hence discharge after 3 weeks. There was no myokymia or fasciculations at discharge.
Myokymia is unique involuntary, spontaneous, localized, transient or persistent quivering movements that affect a few muscle bundles within a single muscle but usually not extensive enough to produce a movement at a joint. The movements are coarser, slower, and undulating (“worm-like”) usually more prolonged and involve a wider local area than fasciculations. They persist during sleep.
Our patient demonstrated limb myokymia in both lower limbs. Limb myokymia could be the result of the disease process causing inflammation and demyelination of nerve roots. Various mechanisms have been proposed for the pathogenesis of myokymia. One is possibly there were accompanying retrograde changes in the cell bodies of anterior horn cells to provide depolarization and subsequent spontaneous discharges. Alternatively, the peripheral nerve root lesion itself might have resulted in the production of myokymia. According to Wallis et al., myokymia in such patients are because of the spontaneous isolated discharges of individual motor units, and they are caused by peripheral nerve lesion, rather than participation of cell bodies. Williamson and Brooke agreed with the “peripheral nerve origin” theory of myokymia, and quoted to the work of Denny Brown and Foley. According to William R et al. either facial or limb myokymia could be a neurological sign of increased excitability of motor system, from supranuclear pathways to the motor nucleus and up to the neuromuscular junction.
Unlike focal myokymia, generalized myokymia may occur in the absence of any abnormality within the peripheral nerves. For instance, Issacs' syndrome, a rare neuromuscular disorder of continuous muscle fiber activity, manifests with generalized myokymia. Other characteristic features of Issacs' syndrome are pseudomyotonia, cramps, stiffness, and fasciculations, and the symptoms are caused by peripheral nerve hyperexcitability resulting from voltage-gated potassium channelopathy. This condition may be inherited or acquired. The acquired form is usually seen in association with autoimmune disorders, infections, medications, toxin exposure, and cancer.
Interestingly, in a case report by Myers KA et al., Issacs' syndrome had been described in association with GBS. In their study, a 24-year-old man, who was treated for GBS at 21 years of his age, was found to have developed seropositive (positive for anti-voltage-gated potassium channel (VGKC) antibodies) Issacs' syndrome at 24 years.
The diagnosis of Issacs' syndrome is made mainly by needle electromyography (EMG), which shows myokymic and neuromyotonic discharges. Myokymic discharges occur repeatedly at 50-150 Hz and appear as doublet, triplet, or multiplet single unit discharges with a high intra burst frequency. Neuromyotonic discharges occur at 150-300 Hz, and they begin and end abruptly, and their amplitude often fades; focal myokymic discharges in on the other hand, because of other causes such as GBS, are typically composed of spontaneous, semi-rhythmic bursts of motor unit potentials. Our patient showed burst duration of 80-130 ms with intra-burst spike frequency of 80-120 Hz with burst amplitude of 250-350 μV, features in favor of myokymia. Similar features were described in Seung-Bong Hong et al. study. Serological study will be useful to confirm Issacs' syndrome. Approximately, 40% of patients with Issacs' syndrome have antibodies to voltage gated potassium channel.
Our patient lacked the clinical characteristics of Issacs' syndrome like previous history of myokymia, delayed relaxation of muscles after contraction, cramps, and stiffness as well as the electromyographic pattern, which ruled out the diagnosis of Issacs' syndrome.
To conclude, our case illustrates an infrequently observed clinical association of limb myokymia with GBS.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2]