Myokymia

Episodic ataxia (EA) is an autosomal dominant disorder that brief episodes of ataxia can be triggered by physical or emotional stress. The symptom can occur several times during the day, last for seconds to minutes, and be associated with dysarthria and motor neuron activity, which causes muscle rippling (myokymia) between and during attacks. It is caused by a mutation in a neuronal voltage dependent Ca2+ channel. 

Clofibrate causes a necrotizing myopathy, particularly in patients with renal failure, nephrotic syndrome or hypothyroidism. The myopathy is painful and myokymia of unknown origin is sometimes present. The mechanism of damage is not known, but p-chlorophenol is a major metabolite of clofibrate and p-chlorophe-nol is a particularly potent uncoupler of cellular oxidative phosphorylation and disrupts the fluidity of lipid membranes. Muscle damage is repaired rapidly on the cessation of treatment. 

Clozapine-induced myokymia (weakness and reduced muscle tone, with undulating movements of the muscle and skin, accompanied by involuntary repetitive firing of grouped motor unit action potentials) has been reported (196). 

A 33-year-old woman developed muscle twitching and spasms of the legs and back after having taken clozapine for 3 years (197). Neurological examination showed myokymia in both thighs, calves, and the lower lip. The myokymia disappeared 1 week after withdrawal of clozapine. 

David WS, Sharif AA. Clozapine-induced myokymia. Muscle Nerve 1998 21(6) 827-8. 

Eyelid myokymia or benign eyelid twitching is a common localized form of facial myokymia. It is a transient condition in which mild to moderate fine undulating contractions of the orbicularis muscle occurs, causing an annoying... 

Eyelid myokymia does not progress to other parts of the face. When myokymia involves the other facial muscles, it is a sign of an underlying neurologic problem that needs further evaluation and referral. 

Banik R, Miller NR. Chronic myokymia Mmited to the eyelid is a benign condition.J Neuro Opthahnol 2004 24 290-292. 

Myokymia (wave-like muscle fiber twitching)... 

Browne DL, Gancher ST, Nutt JG et al 1994 Episodic ataxia/myokymia syndrome is associated with point mutat ions in the human potassium channel gene, KCNAl. Nat Genet 8 136-140... 

Myoclonus can occut in hypothytoidism. Tendon teflexes ate slowed with a delay in the tecovety phase. In the atche-typical Achilles teflex, this is commonly tefetted to as the Hangmans teflex (Miles and Sutveyot, 1965). Isolated myopathy, such as dtopped head syndtome with isolated weakness of the splenius capitus muscle, has also been described. Ptosis also occurs with myokymia. Ataxia is known to occur, but may actually reflect the poorly coordinated muscular activity rather than cerebellar abnormality (Pinelli et al., 1990). 

Although neuromuscular conditions are known to be associated with autoimmune thyroid diseases, EMG myokymia has not been described. We had previously reported two cases with hypothyroidism referred for diagnostic work-up of bilateral ptosis (Lo et al., 2003). Both patients were young females who were otherwise normal when examined physically, but had hypothyroidism on replacement of L-thyroxine. They presented with isolated bilateral ptosis. An axonal lesion involving the VII nerve was unlikely in the presence of normal EMG motor unit recruitment and the absence of active denervation changes. Normal NGS also helped rule out an underlying hypothyroidism-related polyneuropathy. 

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