Tremor dominant Parkinsonism: Clinical description and LRRK2 mutation screening

Tremor dominant parkinsonism (TDP) is characterized by initial prominent resting and action tremor, mild parkinsonism, unpredictable response to medication, and a better prognosis than idiopathic Parkinson's disease (PD). We report on clinical features and longitudinal course of 26 patients suffering from TDP. Mean disease duration was 6.5 ± 3 years, 61.5% of patients had a positive family history of tremor, 73% did not need drug treatment, performance of 123I-Ioflupane SPECT showed reduced striatal tracer uptake in 65.4% of patients, and odor identification testing was pathologic in all the patients tested (n = 22). Co-occurrence of action and resting tremor were the most annoying and disabling symptoms in all the patients, whereas rigidity and/or bradykinesia were clinically irrelevant in most of them. We also sequenced the full coding region of the Leucine-rich repeat kinase 2 gene (LRRK2) in all patients. We found a novel Val2390Met mutation that was not found in 864 chromosomes. Our results suggest a broader clinical heterogeneity related to LRRK2 mutations and points towards TDP as a subtype within the spectrum of PD, in which disabling tremor but otherwise mild parkinsonian signs and a better prognosis are the main characteristics.