Myokymia

Myokymia refers to involuntary, spontaneous, localized, transient or persistent quivering movements of a muscle. When myokymia involves the extremities, the movements are usually coarser, slower and more prolonged than fasciculations and often have an undulating character. Myokymia involving the face is typically more vermicular. The top video shows myokymia involving the quadriceps muscle in a patient with a denervating process, with simultaneous EMG. The louder, low frequency periodic thumping in the background is a myokymic discharge; the softer, higher frequency discharges are fibrillation potentials. The bottom video shows myokymia of the quadriceps due to rattlesnake envenomation. Myokymia can be difficult to distinguish from fasciculations. Typically, fasciculations dance and flit from spot to spot, myokymia tends to persist in the same location for a more prolonged period.

Myokymia often occurs in normal individuals. Mild, usually fleeting, myokymia is common, especially in the orbicularis oculi, and is of no clinical significance. These movements often worsen with fatigue and with hypercaffeinism. Patients often require reassurance. Myokymia occurs in a variety of disease states; it is thought to arise because of biochemical perturbations in the nerve microenvironment due to demyelination, a toxin (such as rattlesnake venom), or other factors

Myokymia may be generalized or focal/segmental.(1-3) Focal myokymia is much more common than generalized myokymia. Myokymia sometimes occurs in the facial muscles in patients with MS or other lesions of the brainstem or cranial nerves. Focal limb myokymia is particularly characteristic of radiation damage to a nerve or plexus. Generalized myokymia causes generalized muscle stiffness and persistent contraction because of underlying continuous muscle fiber activity. EMG discloses spontaneous repetitive firing of motor unit potentials, accompanied by myokymic and neuromyotonic discharges. For a video of dramatic facial myokymia due to a rattlesnake bite see https://www.youtube.com/watch?v=KaM3-qy8uqU). (4) For a video of facial myokymia in MS see https://collections.lib.utah.edu/details?id=180332 (5)

References

1. Jacobs L, Kaba S, Pullicino P. The lesion causing continuous facial myokymia in multiple sclerosis. Arch Neurol. 1994;51:1115-9

2. Chhibber, S and Greenberg, SA. Teaching Video NeuroImages: Widespread clinical myokymia in chronic inflammatory demyelinating polyradiculoneuropathy. Neurology. 2011; 77:e33.

3. Zhang YQ. Teaching video Neuro Images: regional myokymia. Neurology 2010;74(23):e103–e104.

4. Kobayashi, SA. Images in clinical medicine. Perioral myokymia. N Engl J Med. 2013; 368:e5.(http://www.nejm.org/doi/full/10.1056/NEJMicm1202778)

5. from Kathleen B. Digre, John A. Moran Eye Center, Neuro-ophthalmology Virtual Education Library (NOVEL), University of Utah).