Abstract
It is controversial if early onset Parkinson's disease (EOPD) (onset at <41 years of age) is Parkinson's disease (PD) occuring at a younger age or a different disease. This controversy is due to some clinical and pathological differences between EOPD and PD. Within EOPD, there appear to be two groups namely: young onset Parkinson's disease (YOPD), with onset between 21 and 40 years, and juvenile parkinsonism (JP), with onset at <20 years. The two major clinical differences between these groups are a higher familial occurence of PD and dystonia in JP. In this study, we determine if the two groups have the classical features of PD, namely rest tremors, rigidity, bradykinesia, and postural instability, and have a meaningful response to levodopa. Furthermore, we compare their other clinical features, autonomic and cognitive functions, and levels of CSF monoamine metabolites to determine differences between these groups. We observe that all YOPD (100%) and JP (85%) patients had rest tremors. Most of these patients also had a meaningful response to levodopa (YOPD: 72%; JP: 100%). The prevalence of family history of PD was similar, whereas dystonia was more frequent in JP (43%) compared to YOPD (9%). Autonomic symptoms were twice as common in JP (42%) compared to YOPD (17%). However, bedside autonomic fuctions were abnormal in similar proportions and, like in PD, suggest involvement of parasympathetic nervous system. Congnitive dysfunction does occur but with no difference in severity between the two groups. The difference in number of patients between YOPD and JP groups makes statistical comparison of the occurence of clinical features like dystonia and autonomic dysfunction difficult. A similar situation exists in earlier studies on EOPD and could be a possible reason for the apparent difference between YOPD and JP; hence, combining two earlier studies with ours, we perform a meta‐analysis. The meta‐analysis did not confirm significant differences in the occurrence of dystonia or a positive family history of PD in the two groups. Besides clinical similarities between YOPD and JP, like in PD, these former two have dopaminergic deficiency demonstrated by significantly low mean CSF homovanillic acid level. Our study demonstrates that EOPD is similar to PD and there are no striking clinical differences between YOPD and JP. Hence, we suggest that EOPD is PD occuring at a younger age.