Which symptom is indicative of UMN involvement in ALS?

• A. Atrophy and muscle weakness
• B. Muscle spasticity and increased reflexes
• C. Involuntary muscle movements
• D. Lack of coordination

Answer: (B)

The indication of upper motor neuron (UMN) involvement in Amyotrophic Lateral Sclerosis (ALS) is characterized by symptoms such as muscle spasticity and increased reflexes. Upper motor neurons originate in the brain and communicate with lower motor neurons, coordinating voluntary movement. When UMNs are affected, as seen in ALS, the signals sent to lower motor neurons can become disrupted leading to a lack of inhibition on the muscles. This results in spasticity, which is characterized by increased muscle tone and stiffness.

Additionally, the hyperactive reflexes associated with UMN damage occur due to the disinhibition of reflex pathways. Normal reflexes may become exaggerated when the upper motor neurons are dysfunctional, as they are responsible for modulating these reflex responses.

In contrast, atrophy and muscle weakness are more strongly associated with lower motor neuron involvement; involuntary muscle movements may relate to other neurological conditions, and lack of coordination can be indicative of a variety of neurological issues, not specifically pointing to UMN involvement in ALS. Therefore, the symptom of muscle spasticity and increased reflexes clearly aligns with the effects of upper motor neuron dysfunction in this context.