Clinical and Imaging Study of Isolated and Mixed Rest and Action Tremor-Essential Tremor versus Parkinson's Disease

BACKGROUND: Some patients present an unusual association of both action tremor (AT) and rest tremor (RT) making the differential diagnosis between essential tremor (ET) and Parkinson's disease (PD) difficult. AIM: To investigate this particular clinical picture trying to focus on possible peculiar clinical inferences. PATIENTS AND METHODS: Twenty-three patients with atypical tremor syndrome were selected for the study. They underwent neurological examination, neuroimaging study, and brain DaTSCAN single-photon emission computed tomography. RESULTS: Twenty-three patients were evaluated; 17 presented mixed-tremor syndrome, while six patients showed only isolated AT or RT. DaTSCAN was pathological in 19 patients and normal in 3 patients. The emerging statistical data highlighted a positive correlation between disease duration and DaTSCAN abnormalities; Fisher's exact test showed a marked difference in evolution toward a dysfunction of dopaminergic pathways in patients with both AT and RT phenotype. CONCLUSION: The possible correlation between PD and ET has often been discussed without any clear findings. Are these patients suffering from ET prone to develop PD? Or are they the expression of a specific clinical phenotype? Our clinical survey has not led to absolute considerations; however, it seeks to highlight the clinical markers that might arouse the suspicion of extrapyramidal disease in patients with atypical tremor syndrome.