Which condition is characterized by stiffness and muscle spasms, often associated with neurological symptoms?

Stiff-Person syndrome is characterized by stiffness and muscle spasms that can severely restrict movement. This condition is often accompanied by neurological symptoms, such as heightened sensitivity to stimuli and muscle rigidity, which can lead to painful spasms.

The underlying pathology involves disruptions in the regulation of motor neuron activity, where autoantibodies target proteins within the body that are crucial for the normal functioning of the central nervous system. This results in the characteristic stiffness and rigidity of muscles, which can lead to significant mobility challenges.

Other conditions mentioned do present with muscle-related symptoms but differ in their primary characteristics and underlying mechanisms. For instance, Parkinson's disease primarily involves tremors, bradykinesia, postural instability, and does not typically present with the same level of muscle stiffness and spasms as seen in Stiff-Person syndrome. Myasthenia gravis is associated more with muscle weakness rather than stiffness, resulting from an autoimmune attack on the neuromuscular junction. Muscle dystrophy encompasses a group of genetic disorders that lead to progressive muscle degeneration and weakness but do not primarily cause stiffness or significant neurological symptoms in the same way. Hence, Stiff-Person syndrome is the most fitting answer here.