If response is obtained to central pain, peripheral stimulation is not needed. Peripheral pain may produce a spinal reflex, and is therefore, not an effective test of upper motor neuron function. Withdrawal can be described by the presence of normal flexion in response to pain. Pulling away without flexing the wrist is one way to differentiate normal flexion from abnormal flexion. Rigid flexion is considered abnormal flexion.
Rigid extension is referred to as abnormal extension .
Absence of movement or tone is referred to as flacid paralysis. In addition to the assessment of strength described above, muscles should be inspected and palpated. Inspect for asymmetrical movement or abnormal limb rotation. Decreased tone may represent early upper motor neuron or peripheral nerve injury. Increased tone is associated with upper motor neuron injury.