Cogwheel rigidity refers to the cogwheel-like jerk responses of body muscles when force is applied while bending a limb. This cogwheel jerk does not happen in normal circumstances. It is usually a common occurrence among patient’s suffering from Parkinson’s disease.
In fact, cogwheel rigidity is among the first signs of Parkinson’s disease. This is then marked with muscle rigidity, wherein the muscle reacts in ratchet-like movements when it is stretched.
Therefore, when checking for Parkinson’s disease, a doctor will typically conduct a cogwheel rigidity test along with a series of other diagnostic procedures. In case of Parkinson’s disease, cogwheel rigidity happens along with a tremor that usually starts in the fingers, also referred to as a unilateral pill-roll tremor. This tremor increases during stressful or anxious situations and decreases during purposeful movements and rest.
Cogwheel rigidity being a characteristic of Parkinson’s, it needs to be detected by the doctor; hence, a simple test is conducted. This is a physiotherapy procedure, which is non-invasive and painless in nature. Cogwheel rigidity is believed to usually occur in the arms but there are occasions when this rigidity can be elicited from the ankle as well. If the examiner is trying to elicit cogwheel rigidity from the arm, then he/she will hold your forearm steady while rotating your wrist in a range of motions. In case of muscle rigidity, the same can be felt and seen by the patient as well as examiner as a stiff or rigid feeling is accompanied by a tremor.
Since, the rigidity and the jerky movements resemble those of a cogwheel; this particular characteristic is referred to as cogwheel rigidity. So, when the examiner moves your limbs, he/she can actually feel the ratchet-like movement. We all complain about feeling stiff in the muscles, but this feeling is vastly different from the one experienced by a person suffering from Parkinson’s These patients also experience a tremor accompanied by other Parkinson’s symptoms, making cogwheel rigidity an uncomfortable experience.
Also, since cogwheel rigidity test is conducted to check for Parkinson’s disease, it is important to identify the first noticeable signs of the disease, for instance, tremor in the fingers, slower movements or constant stiffness in arms and legs. In addition to these, there are other signs of the disease like, monotonous speech, drooling, dysphagia and change in gait.
Occasionally, cogwheel rigidity is also caused as a result of certain medications. Antipsychotic drugs like phenothiazines, haloperidol, loxapine and thiothixene can cause cogwheel rigidity. On rare occasions, a drug called metoclopramide also causes it. Do note that cogwheel rigidity only happens to adults. It does not occur in children.