What common condition is associated with rigidity?

Rigidity is a hallmark symptom commonly associated with parkinsonism, which includes Parkinson's disease and other related disorders. This condition is characterized by increased muscle tone leading to stiffness and resistance to passive movement. It often manifests as a non-oscillatory muscle tightness that is not dependent on the direction of movement, differentiating it from other types of muscle tone abnormalities.

In parkinsonism, rigidity can be tested through clinical evaluations such as the "lead-pipe" rigidity or "cogwheel" rigidity, where the muscle is stiff, and resistance can be felt continuously throughout the motion. This rigid muscle tone is one of the primary symptoms that help clinicians raise suspicion for Parkinson's disease or similar disorders, which are rooted in basal ganglia dysfunction.

While other conditions like cerebrovascular accidents (strokes) and multiple sclerosis can present with various neurological deficits and changes in muscle tone, they do not typically exhibit the classic rigidity pattern seen in parkinsonism. Myasthenia gravis primarily affects neuromuscular transmission, leading to fluctuating muscle weakness rather than rigidity. Thus, parkinsonism stands out as the condition most characteristically associated with rigidity.