Neoplasm as a cause of brachial plexus palsy in neonates.

Two patients with neonatal onset of arm weakness resulting from neoplastic involvement of the brachial plexus who were initially considered to have obstetric brachial plexus palsies are reported. The first patient was a 7-day-old female who presented with a left supraclavicular mass that was first detected at 2 days of age and left proximal arm weakness. The weakness involved the whole arm within 3 days. The mass was a malignant rhabdoid tumor. The second patient was a 28-month-old male who presented with slowly progressive right arm weakness, which began at 3 weeks of age, and episodes of scratch marks on the arm that began at 4 months of age. Magnetic resonance imaging revealed a plexiform neurofibroma of the brachial plexus. The features that are suggestive of a brachial plexus palsy caused by a neoplasm rather than of obstetric brachial plexus palsy include the following: the onset of weakness after the first day of age, with a progressive course; a history of a normal delivery and birth weight; the absence of signs of a traumatic injury or injuries; the appearance before 7 days of age of a growing supraclavicular mass without radiographic evidence of a clavicular fracture; and recurrent scratch marks on the weak arm.