myokymia, fasciculation & denervation - facial nerve

Presentation: spontaneous twitching one side of face followed by unilateral facial weakness affecting upper and lower portions. Percussing over facial nerve elicits twitching. EMG shows myokymia, fasciculations, rare positive sharp waves, reduced recruitment with polyphasic motor units.
Kimura gives a succinct explanation of myokymia: "Myokymic discharges, otherwise known as grouped fasciculation potentials, consist of two to eight consecutive spontaneous single motor unit discharges, occurring repetitively"
• Kimura & Kohara: F34 T...
Focal or regional myokymia affecting limb muscles is caused by demyelinating lesions of peripheral nerves or roots, and frequently is associated with conduction block. It occurs, for example, in Guillain Barre Syndrome, CIDP, and also after radiotherapy.
Muscle Nerve. 1996 Feb;19(2):246-9.
Facial myokymia is often a symptom of brainstem lesions, including multiple sclerosis and pontine gliomas, that cause hyperexcitability of the facial nerve nucleus or demyelination of intramedullary nerve fibres.
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Widespread, generalised myokymia, neuromyotonia and fasciculations causing twitching, cramps and muscle stiffness occur in autoimmune peripheral nerve hyperexcitability syndromes including Isaacs syndrome and cramp fasciculation syndrome. These are acquired peripheral nerve ion channelopathies caused by antibodies against components of the voltage-gated potassium channel complex
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