Klumpke paralysis is caused by an injury to the nerves of the brachial plexus which may be resulted from a difficult delivery. This injury can cause a stretching (neuropraxia,), tearing (called “avulsion” when the tear is at the spine, and “rupture” when it is not), or scarring (neuroma) of the brachial plexus nerves. Most infants with Klumpke paralysis have the more mild form of injury (neuropraxia) and often recover within 6 months.
Signs and symptoms include weakness and loss of movement of the arm and hand. Some babies experience drooping of the eyelid on the opposite side of the face as well. This symptom may also be referred to as Horner's syndrome. 
- Ruchelsman DE, Pettrone S, Price AE, Grossman J. Brachial Plexus Birth Palsy: An overview of early treatment options. Bulletin of the NYU Hospital for Joint Diseases. 2009;67(1):83-9.