Objective: To examine the prevalence of cogwheel rigidity (CWR) in a cohort of Parkinson disease (PD) patients

Background: First noted in a 1901 publication, CWR is a ratchet-like resistance to passive movement in a joint and is generally associated with PD.¹ The change in the tone has been ascribed to tremor,² despite the frequency of the ratcheting being higher than the typical rest tremor in PD. Its pathophysiology is thought to lie in the spinal cord.² Denny-Brown suggested that both rigidity and tremor had the same underlying mechanism; tremor arose when the mechanism was “imbalanced.” ³ Our interest in the cogwheel phenomenon is sparked by medical trainees’ importance ascribed to it.

Method: While evaluating 70 consecutive PD patients, we scored the presence or absence of CWR in the arms during the clinical exam, which always included the Unified Parkinson’s Disease Rating Scale, part 3, motor subscale (UPDRS-III), which rates exam findings of bradykinesia, tremor and rigidity on a scale of 0 to 4.

Results: Of 70 subjects, 31 (44%) had CWR in at least one limb (29% women; mean age 70 years; PD duration, mean 6.3 years, range 0-23 years). This was not statistically significantly different from the frequency expected by chance (p=0.06). The 56% with No-CWR had similar clinical characteristics (36% women; mean age 70 years; PD duration, mean 6.8 years, range 0-30 years).  When present, CWR was often present unilaterally. Comparing patients with and without resting tremor, with those with and without CWR, we observed an association between the presence of resting tremor and CWR (X² =10.89, p=0.001), but not all patients with CWR had rest tremor. CWR was also associated with severity of resting tremor bilaterally (right: X² =17.35, p=0.002; left: X² =18.04, p=0.001).

Conclusion: Cogwheel phenomenon is not present in the majority of PD patients. Its absence is apparently of no clinical significance. Our results indicate CWR is associated with the presence of tremor and tremor severity. However, nearly half of the limbs with tremor had no-CWR. Our findings have implications for neurologists and other physicians, many of whom have learned in medical school, incorrectly, that CWR is synonymous with idiopathic PD.

References: 1. Ghiglione P, Mutani R, Chiò A. Cogwheel rigidity. Archives of neurology 2005;62:828-830.
2. Rodriguez-Oroz MC, Jahanshahi M, Krack P, et al. Initial clinical manifestations of Parkinson’s disease: features and pathophysiological mechanisms. The Lancet Neurology 2009;8:1128-1139.
3. Denny-Brown D. Clinical symptomatology of diseases of the basal ganglia. Amsterdam, North Holland1968.
4. Wüllner U, Abele M, Schmitz-Huebsch T, et al. Probable multiple system atrophy in a German family. Journal of Neurology, Neurosurgery & Psychiatry 2004;75:924-925.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/prevalence-of-cogwheel-phenomenon-in-parkinson-disease/