Facial synkinesis and hemifacial spasm are at times difficult to distinguish. The difference is that with hemifacial spasm there is simultaneous contraction of the entire face that is completely beyond the patient's voluntary control. With facial synkinesis, there is contraction of the aberrantly innervated muscle group with the voluntary contraction of the other muscle group; involuntary contraction of one muscle is simultaneous with voluntary contraction of a different muscle. Hemifacial spasm is completely involuntary. Facial synkinesis can be voluntarily suppressed for a period of time, at least as long as one could voluntarily inhibit blinking. Asking the patient to blink produces the cocontraction of the orbicularis oris, asking the patient to smile produces the cocontraction of the orbicularis oculi.
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