Which condition is least likely to cause flaccid dysarthria?

Flaccid dysarthria is typically caused by neurological conditions affecting the lower motor neurons within the cranial and spinal nerves, leading to muscle weakness, reduced tone, and atrophy. Each of the conditions listed influences muscular control, but their mechanisms vary significantly concerning flaccid dysarthria.

Amyotrophic lateral sclerosis (ALS) primarily affects motor neurons in both the upper and lower motor neuron pathways, resulting in a mix of flaccid and spastic dysarthria. Myasthenia gravis affects the neuromuscular junction, leading to muscle weakness that often results in flaccid dysarthria due to fluctuating muscle fatigue. Peripheral nerve injury directly impacts nerve signals to the muscles, causing weakness and flaccidity.

In contrast, multiple sclerosis (MS) is primarily a demyelinating disease that primarily affects the central nervous system, leading to spastic dysarthria due to upper motor neuron involvement rather than flaccid dysarthria, which is generally seen with lower motor neuron damage. Therefore, since MS is less associated with flaccid dysarthria and more with other forms of dysarthria, it is the condition least likely to cause flaccid dysarthria.