Arm Monoplegia Due to Lower Motor Neuron Lesions
A lower motor neuron
lesion may occur at the: (1) brachial center of the spinal cord; (2)
roots and spinal nerves that arise from the spinal segments C5 to T1;
(3) brachial plexus; or (4) peripheral nerves (Figure 214.1 D through
G). Lesions in the brachial center, roots, and spinal nerves usually
occur together with brachial plexus lesions.
Sites of possible nervous system injury that can produce arm monoparesis.
A: brain to midbrain; B: upper pons; C: lower pons and medulla; D: rostral
spinal cord; E: brachial center; F: brachial plexus; G: peripheral nerves;
V: ventricles; T: thalamus; UQ: upper quadrant; FN: facial nerve; LQ:
lower quadrant; BP: brachial plexus; LSP: lumbosacral plexus.
The colored rectangles indicate the location of weakness produced by
damage to the different components of the somatic motor system.
brachial plexus is the most common site of injury in neonates with flaccid
arm weakness. A brachial plexus lesion may present as complete or segmental
Complete brachial plexus injury refers to weakness of the whole
arm. Segmental arm monoparesis due to brachial plexus injury in the
neonate has four clinical presentations: (1) Duchenne-Erb palsy; (2)
upper-middle trunk syndrome, (3) Klumpke palsy, and (4) fascicular syndromes.
Brachial plexus palsy must be differentiated from flaccid arm monoparesis
due to an upper motor neuron lesion and from peripheral nerve damage.