Along with bradykinesia and rigidity, tremor is one of the cardinal motor symptoms of Parkinson's disease (PD), often the first symptom to be noticed by the patient and their relatives. While bradykinesia and rigidity usually respond to dopaminergic therapies, tremor is often refractory to these medications and can cause significant disability in many patients. This variability of response appears to be related to different mechanisms/neurochemical abnormalities underlying the occurrence of tremor in PD patients.
Pavese et al. (Sun,) studied this question.