myokymia

Myokymia is a movement phenomenon characterized by fine, continuous, undulating quivering of a muscle or muscle group, usually visible beneath the skin. It results from spontaneous, rhythmic firing of motor units and can affect facial muscles, eyelids, or more distal muscles. Unlike fasciculations, which are irregular twitches of single motor units, myokymia typically presents as grouped, worm-like movements that may persist for seconds to minutes and can occur at rest or with activity.

Clinical features vary by location. Facial myokymia is the most commonly described form and may involve the eyelid or mouth muscles. It can be continuous or episodic and is sometimes associated with facial numbness or weakness if linked to brainstem or demyelinating pathology. Myokymia of the limbs or trunk is less specific and often prompts evaluation for an underlyingneurological or peripheral nerve disorder.

Causes range from benign, isolated occurrences to manifestations of serious underlying conditions. Central causes include brainstem or cerebellar lesions, such as those seen in multiple sclerosis or brainstem stroke. Peripheral causes include peripheral nerve hyperexcitability syndromes (such as Isaacs syndrome), demyelinating neuropathies, or neuropathic injuries. Secondary factors may include electrolyte disturbances (e.g., hypocalcemia, hypmagnesemia), medications, toxins, or autoimmune processes.

Diagnosis is clinical and supported by electrophysiology. Electromyography typically shows myokymic discharges—bursts of motor unit activity with a distinctive waxing and waning pattern. Evaluation may include MRI or other imaging to identify central causes, and laboratory tests to assess electrolytes and immune or infectious etiologies.

Treatment focuses on the underlying cause when identified and may include anticonvulsants (e.g., carbamazepine, gabapentin, lamotrigine), baclofen, or immunotherapy in autoimmune conditions. Prognosis depends on the etiology and often improves when the primary disorder is treated. Mild, isolated myokymia may be transient and self-limited.