What sign is typically associated with upper motor neuron lesions?

Upper motor neuron lesions typically result in several characteristic signs, one of which is increased muscle tone, also known as spasticity. This occurs because upper motor neurons are responsible for sending signals from the brain to the spinal cord that facilitate voluntary movement and the modulation of muscle tone. When these pathways are damaged, the inhibition of reflex activity is lost, leading to a state of hyperactivity in the stretch reflexes, which manifests as increased tone in the muscles.

In contrast, decreased reflexes and flaccid muscle tone are more indicative of lower motor neuron lesions, where the direct connection between the spinal cord and muscles is compromised, resulting in diminished or absent reflexes and reduced muscle tone. Paresis, or weakness, can be seen in both upper and lower motor neuron lesions, but it doesn’t specifically differentiate between the two types. Therefore, the hallmark sign associated with upper motor neuron lesions is indeed increased muscle tone.