Developmental apraxia arising from neonatal brachial plexus palsy.

OBJECTIVE

To determine whether motor unit activation is impaired in patients with persisting disability arising from neonatal brachial plexus palsy (NBPP).

BACKGROUND

In NBPP patients, the authors previously found more extensive muscle reinnervation than might have been anticipated from the clinical examination.

METHODS

Motor skills were tested in a group of nine boys and seven girls with prior NBPP, who then underwent physiologic investigation of proximal and distal muscles in their affected and unaffected arms. The latter tests comprised measurements of maximal evoked muscle compound action potential (M-wave) amplitude, maximal voluntary torque, twitch torque, and twitch interpolation. A group of 17 children of similar ages served as control subjects.

RESULTS

In the NBPP group, motor skills were diminished and voluntary torque was reduced relative to M-wave amplitude and twitch torque. Moreover, interpolated twitches could be demonstrated in some NBPP patients but not in control subjects.

CONCLUSION

Persisting disability in NBPP patients is due, at least in part, to impaired motor unit activation. The authors suggest that the impairment is a form of developmental apraxia caused by defective motor programming in early infancy.