Final answer:
The incorrect sign or symptom of UMN syndrome listed is actually correct. Clonus is indeed a symptom associated with UMN lesions, along with other symptoms like paralysis, weakness, spasticity, and loss of fine voluntary movements.
Step-by-step explanation:
The incorrect sign or symptom of upper motor neuron (UMN) syndrome is E. Clonus. Clonus is a muscular spasm involving repeated, often rhythmic contractions, which is typically associated with UMN lesions and therefore not incorrect. The signs and symptoms that are characteristic of UMN syndrome include paralysis, weakness, spasticity, loss of fine voluntary movements, and clonus. Spasticity is an increase in muscle tone leading to stiff and awkward movements, while the clasp-knife response is a sudden decrease in resistance to passive movement of a limb, making it akin to a clasp-knife snapping shut. These symptoms distinguish UMN lesions from lower motor neuron (LMN) lesions, where flaccid paralysis, muscle atrophy, and fasciculations are more commonly observed.
Conditions such as Amyotrophic Lateral Sclerosis (ALS) degenerate motor neurons and impact muscle movement. With ALS, patients initially experience muscle weakening and coordination difficulties, eventually leading to paralysis. Therefore, each of the listed signs or symptoms (A-D) correctly relates to UMN syndrome, making E. Clonus an appropriate symptom, not an incorrect one.