Which result is commonly seen in upper motor neuron lesions?

In the context of upper motor neuron lesions, spasticity is a hallmark finding. Upper motor neurons originate in the brain and project to the spinal cord, where they synapse with lower motor neurons that directly innervate muscles. An upper motor neuron lesion disrupts this pathway, leading to a characteristic increase in muscle tone, known as spasticity. This increased tone is due to the loss of inhibitory control that upper motor neurons exert over the lower motor neurons.

Spasticity presents as a velocity-dependent increase in muscle tone, meaning that the resistance to passive movement is greater when the affected limb is moved quickly. This phenomenon occurs because the normal modulation of muscle contraction is lost, resulting in exaggerated reflex arcs.

The associated findings in upper motor neuron lesions can include the presence of hyperreflexia, which means that reflexes are often brisk and exaggerated. However, hyporeflexia is more commonly associated with lower motor neuron lesions, where there is a direct loss of anterior horn cells or peripheral nerves.

On the other hand, muscle atrophy and fasciculations are typically linked with lower motor neuron damage. Muscle atrophy occurs because of disuse and denervation of the muscle, while fasciculations, which are involuntary muscle twitches, arise