Misinnervation

Misinnervation refers to erroneous reinnervation of muscles after nerve injury, in which regenerating axons connect to inappropriate targets, resulting in abnormal motor control. It is most often described after peripheral nerve injuries or surgical nerve repairs, when regenerating fibers lose precise guidance and form connections with non-target muscles or regions, producing synkinesis or unintended contractions.

Causes and mechanisms involve misdirected axonal growth during recovery, sometimes with polyneuronal innervation of a single muscle or inappropriate reinnervation of synergistic or antagonistic muscles. The result is co-activation of muscles that should act independently, or concurrent movements that are not voluntary. Misinnervation can occur in the facial nerve, brachial plexus, or other peripheral nerves, and may accompany or follow acute nerve palsies, tumors, or surgical manipulation.

Clinical features depend on the muscles involved but commonly include involuntary contractions that occur with voluntary movement, abnormal facial movements during smiling or blinking, or unintended limb movements when other muscles are activated. Patients may experience difficulty controlling precise movements and may notice alternating weakness in affected distributions.

Diagnosis relies on clinical history and examination. Electromyography (EMG) and nerve conduction studies can reveal overlapping motor activity and synkinetic patterns consistent with misinnervation, while imaging may identify structural causes of nerve injury.

Management is individualized and may include physical therapy with neuromuscular retraining, botulinum toxin injections to reduce unwanted contraction, and, in selected cases, surgical interventions such as selective neurectomy or nerve transfers. Prognosis varies, with some improvement possible through rehabilitation, but misinnervation can persist as a long-term complication of nerve injury.