lesion of the brachial plexus may present with signs restricted to one
muscle or to a few muscles. The clinical manifestations of fascicular
brachial plexus lesions may be indistinguishable from those of peripheral
nerve branchlesions. The
diagnosis of a fascicular brachial plexus lesion is established by the
combination of weakness in a muscle innervated by a distal or intermediate
nerve of the brachial plexus and (1) clinical or electrophysiological
abnormality in a muscle innervated from the same spinal segment but through
a proximal brachial plexus nerve; or (2) a Horner syndrome (Figure 222.1).
The combination of weakness of a muscle innervated by distal brachial
plexus nerves and Horner syndrome imply C8 or T1 ventral root or spinal
nerve damage, or both.
Figure 222.1.— [A] Inability to extend the distal
phalange of the right thumb. [B] Right-sided Horner syndrome. This patient
had a brachial nerve lesion confirmed by EMG findings of proximal brachial
plexus nerve involvement.
nerve lesions always produce segmental flaccid monoparesis. Segmental
limb weakness due to peripheral nerve injury may occur with lesions that
damage a nerve, a major branch, or just a few fascicles within a nerve
or a branch. Injury to the whole nerve or a major branch produces characteristic
clinical findings that differentiate these injuries from brachial plexus
injury and other peripheral nerve injuries.
Involvement of a secondary branch or a fascicle within a nerve or a branch
produces a pattern of weakness that can seldom be clinically differentiated
from a fascicular brachial plexus lesion.