Introduction: There is now growing evidence that essential tremor and Parkinson's disease are related.
Aim: To present the main findings from epidemiologic, genetic, clinical, imaging and pathologic studies, contrasting evidences for and against an association between essential tremor and Parkinson's disease.
Development: We include a complete update of the latest findings regarding the overlap between these two disorders. There is current evidence that a history of essential tremor may herald the onset of Parkinson's disease in a subset of patients. Furthermore, the fact that the risk of essential tremor is significantly increased in relatives of patients with Parkinson's disease suggests the possibility that both conditions are genetically related, probably sharing common hereditary predisposition. Dopaminergic deficit among essential tremor patients in functional imaging studies and recent pathological studies describing Lewy bodies in some essential tremor patients, support further evidence for an overlap between both conditions, at least in a subset of patients.
Conclusion: The convergence of all the reviewed data suggests the possible existence of a mixed essential tremor-Parkinson's disease phenotype in some patients. However, further studies are needed to better understand this phenotype.