Exploring the link between essential tremor and Parkinson's disease.

Area of Science:

• Neuroscience
• Neurology
• Medical Imaging

Background:

• Epidemiological studies suggest a link between essential tremor (ET) and Parkinson's disease (PD).
• Some ET cases may represent a neurodegenerative disease with Lewy bodies, similar to PD.
• Parkinson's disease with antecedent essential tremor (PD_conv) may have unique characteristics.

Purpose of the Study:

• To investigate the relationship between PD and premorbid ET.
• To identify pathobiological differences distinguishing PD_conv from PD.
• To analyze central dopaminergic and peripheral noradrenergic integrity in ET, PD_conv, and PD patients.

Main Methods:

• Positron emission tomography (PET) using ¹⁸F-N-(3-fluoropropyl)-2beta-carbon ethoxy-3beta-(4-iodophenyl) nortropane.
• ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG) myocardial scintigraphy.
• Inclusion of 51 ET, 32 PD_conv, and 95 PD patients.

Main Results:

• PD_conv exhibited typical striatal pathology of PD but with delayed noradrenergic impairment.
• Both PD subtypes showed similar presynaptic dopamine transporter deficits; ET patients had high densities except in the thalamus.
• Presynaptic dopaminergic availability decreased across ET, PD_conv, and PD groups. Myocardial denervation was initially less in PD_conv but progressed faster.

Conclusions:

• PD_conv represents a distinct subclass where PD pathobiology interacts with ET pathobiology early in the disease.
• The findings highlight unique neurodegenerative patterns in PD_conv patients.
• Understanding this interplay is crucial for differentiating and potentially treating these conditions.