Asymmetric postural tremor preceding DOPA-responsive Parkinsonism - the transition disease

Tremulous Parkinson's disease (PD) and essential tremor are well known to be associated, but characteristics of progression of pure tremor state to PD remain unclear.

In this prospective study a cohort of 16 patients suffering from a suggested new disease entity was clinically, pharmacologically, and sonographically analyzed to evaluate whether characteristics giving rise to a new entity in this field can be detected.

All patients had a history of asymmetric postural tremor (aPT) who either already had developed surplus Parkinsonism (PARK group), or were still in the state of a pure asymmetric postural tremor syndrome (APT group). Asymmetry of aPT was assessed by tremor scores including an asymmetry index. DOPA-responsivity was analyzed by tremor scores and the score of the motor part of the Unified Parkinson's disease rating scale. Transcranial brain sonography was performed to evaluate echogenicity of the substantia nigra.

Mean age at onset of asymmetric postural tremor was 57 ± 8.5 years without significant differences between both groups. Family history was compatible with an autosomal-dominant inheritance pattern in the majority of patients of both the APT and PARK group. All patients in the PARK group and 3 out of 8 patients in the APT group (38%) with respect to their asymmetric postural tremor were DOPA-responsive. All patients of both groups eligible to transcranial brain sonography showed hyperechogenicity of substantia nigra. In both groups, there was no correlation between tremor severity and duration of asymmetric postural tremor.

Our data indicate that patients with an initial asymmetric and sometimes DOPA-responsive postural tremor syndrome and PARK patients are at various stages within the transition from aPT to a later developed DOPA-responsive Parkinsonian syndrome. It is postulated that the described group of patients may represent a separate disease entity with a hereditary background.