Sixteen cases of radial mononeuropathy, presenting with wristdrop and seen in the EMG laboratory at Children’s Hospital, Boston, during 16 years, 1979-95, were analysed. Eight were atraumatic, including 2 in newborns, related to compression in 6 and entrapment in 2. Eight were caused by fractures or lacerations. The lesions localized by EMG were in the distal main radial nerve trunk in 9 (56%), the posterior interosseous nerve in 5 (31%), and in the proximal main radial nerve trunk in 2 (13%). Demyelinating lesions in 4 cases improved within 6-12 weeks, and axonal injuries in 13 took between 6 weeks and 18 months to improve or recover. Two showed no improvement in 4 years, and 1 caused by sclerotherapy for a nevus was progressive. 
COMMENT. These authors have previously determined that an EMG taken within 1-2 days of birth and showing fibrillation potentials is required to support a diagnosis of intrauterine prenatal-onset neuropathy . The precise temporal profile for signs of denervation in the neonate with birth injury has not been well defined, and an EMG performed later than 48 hours after birth may not distinguish prenatal from perinatal injuries. The distribution of the EMG abnormalities differentiates the radial neuropathies from the brachial plexus palsies.