MS-3881

A 3-month-old infant is seen by their pediatrician due to their mother’s concern about their hand being fixed in an unusual position. The infant had a difficult delivery with shoulder dystocia, but has been healthy since birth and meeting developmental milestones.

During the exam, the pediatrician observes that the infant’s fingers on the left hand are permanently flexed, resembling a claw. There is also muscle wasting in the left forearm. Additionally, the pediatrician notes left-sided miosis, ptosis, and anhidrosis.

What is the most probable cause of these symptoms in this infant?