Evolution of Facial Paralysis

Phase 1. Muscle weakness in the middle of the face (flaccid or hypotonic phase). This occurs because the signals that control the facial muscles do not work correctly, either due to a damaged facial nerve or the conduction system for these signals. This causes one side of the face to lose mobility and the muscles to atrophy (hypotonia), while the muscles become more active than normal on the opposite side (hypertonia).  

Phase 2. Recovery of mobility (reinnervation-recovery phase). This phase usually begins 3-4 months after the onset of paralysis, although it depends on the type of facial nerve injury. It is when the facial nerve grows slowly and reaches the facial muscles, reconnecting with them as they gradually recover their ability to move.  

Phase 3. Involuntary, unconscious movements (synkinesis). This phase usually appear 3-4 months after the start of the previous (recovery) phase, although it sometimes coincides with it. Sequelae in the form of involuntary and unconscious movements, called synkinesis, appear in this phase. An example is when trying to smile; sometimes the eye muscles also involuntarily contract. This is because the nerves are reconnecting after the injury but doing so incorrectly. Sustained muscle contraction or persistent muscle tension is produced by hyperactivity of the facial nucleus which leads the muscles into a state of excessive tension. This can cause stiffness, discomfort and even pain in the face.