A disorder characterized by progressive degeneration of motor neurons is known as?

Amyotrophic lateral sclerosis (ALS) is indeed characterized by the progressive degeneration of motor neurons, which leads to muscle weakness and atrophy. This condition primarily affects the motor neurons in the brain and spinal cord, resulting in the loss of voluntary muscle functions. As the disease progresses, individuals may experience difficulty in speaking, swallowing, and eventually breathing, due to the involvement of respiratory muscles.

In contrast, the other options refer to entirely different conditions. Myxedema is a severe form of hypothyroidism that affects various bodily systems but does not involve motor neuron degeneration. Grave's disease is an autoimmune hyperthyroid condition leading to an overproduction of thyroid hormone. Dementia refers to a decline in cognitive function that affects memory, thinking, and social abilities, rather than specifically impacting motor neurons. Therefore, the distinct definition of ALS aligns perfectly with the description given in the question.