Other neurological findings that may help to localize the lesion in a patient with spastic arm weakness are the presence of seizures and gaze preference. Seizures are more common with cortical or subcortical lesions than with lesions below these areas. Convulsions usually involve the weak arm and may become generalized. Gaze preference may occur with spastic arm weakness.
Spastic arm weakness is due to a focal central nervous system lesion. The evaluation of a neonate with spastic arm weakness should include MRI and MRA of the brain. Magnetic resonance imaging and angiography of the brain usually localize the lesion. If the MRI and the MRA are normal, an MRI of the upper cervical spine should be done.

Neonates with flaccid arm monoplegia have decreased frequency and strength of movement of the affected limb (Figure 211.1 [A]). They also show absence or decreased movement during the Moro reflex (Figure 211.1 [B]) and decreased biceps, brachioradialis, and triceps muscle stretch reflexes. The location of the lesion in a neonate with flaccid weakness may be in the upper motor neuron or in the lower motor neuron.

A	B

Figure 211.1.— Flaccid arm monoparesis. [A] The left arm rests motionless. [B] The Moro reflex does not elicit movement of the weak arm.