What causes congenital brachial plexus palsy?

Congenital brachial plexus palsy may occur due to trauma during delivery, trauma before delivery, amniotic bands, or congenital chicken pox. The majority of cases of congenital brachial plexus palsy are due to trauma during delivery. Most of these neonates have a clear history of shoulder dystocia and evidence of acute trauma to other areas of the body. Trauma prior to the initiation of labor should be suspected as the cause of brachial plexus palsy in small neonates delivered by cesarean section and without evidence of acute trauma. Most of these neonates have fixed deformities of the extremity that implies that the limb movements have been restricted for a prolonged period of time. The presence of fibrillation by electromyography in the first week of life is strong evidence that the injury occurred prior to delivery. Fibrillation does not occur until 10 days after nerve injury. Amniotic bands in the distribution of the shoulder and neck may produce brachial plexus palsy. The presence of an amniotic band is diagnostic. The affected arm is usually deformed and only partially developed. Chicken pox as the cause of brachial plexus palsy should be considered in neonates born to mothers that develop chicken pox during early and middle pregnancy. Neonates with congenital chicken pox have cutaneous scarring which results from exposure of the vesicular lesions to amniotic fluid.