What neurological condition is characterized by "cogwheel rigidity"?

Cogwheel rigidity is a distinctive feature associated with Parkinson's disease, a neurodegenerative disorder. This type of rigidity is characterized by a jerky, oscillating movement when a limb is passively moved, reflecting the impairment in the normal smoothing of muscle tone due to increased muscle stiffness. In Parkinson’s patients, this rigidity occurs alongside other hallmark symptoms such as bradykinesia, resting tremor, and postural instability.

The term "cogwheel" describes the way the rigidity manifests in a manner reminiscent of the teeth of a cogwheel, where there is a ratcheting effect during passive movements rather than a fluid motion. This symptom is primarily caused by dysfunction in the basal ganglia, which plays a crucial role in the coordination and regulation of voluntary movement. As the disease progresses, this rigidity can become more pronounced and is an important clinical indicator when diagnosing Parkinson's disease.