Essential and aging-related tremor: Differences of central control.
BACKGROUND
For essential tremor, the distribution of age of onset is bimodally distributed, with peaks in adolescence and another in late adulthood. The latter is here referred to as aging-related tremor, and it is considered to be associated with earlier aging and increased mortality. We hypothesize that different tremor networks detected by multichannel electroencephalography (EEG) underlie these two tremor groups.


METHODS
We investigated 20 patients with essential tremor separated into two groups and 10 age- and sex-matched aging-related tremor patients using pooled coherence spectra of the maximally coherent EEG electrodes during a holding task, a pinch grip task, and whilst performing slow hand movements. Functional and effective connectivity at the coupling frequency was estimated.


RESULTS
The maximal coherence was significantly higher in early-onset essential tremor compared with aging-related tremor during the three tasks. Compared with the patients with aging-related tremor, 2 Hz to 40 Hz power, spectral peak frequency, and relative signal-to-noise ratio were not different, but the electromyographic amplitude was significantly greater in essential tremor. The source analysis revealed the well-known cortico-brainstem-cerebello-thalamo-cortical network for classical essential tremor, but patients with aging-related tremor showed a cortico-thalamic network only. The connections between the sources for both tremors were bidirectional. Only the cerebellum and the brainstem showed unidirectional connections in essential tremor and the thalamus in aging-related tremor patients. A second essential tremor group with similar electromyographic amplitudes confirmed the differences between both tremor types.


CONCLUSIONS
We show that the oscillating cerebral networks underlying classical essential tremor and aging-related tremor differ, suggesting a pathophysiological difference.
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Muthuraman
M
Muthuraman
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Günther
G
Deuschl
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Abdul Rauf
AR
Anwar
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Kidist Gebremariam
KG
Mideksa
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Friederike
F
von Helmolt
Department of Neurology, University Hospital Schleswig Holstein, Campus Kiel, Germany.
Susanne A
SA
Schneider
D017668:Age of Onset; D000368:Aged; D000375:Aging; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D058256:Brain Waves / Q000502:physiology*; D016022:Case-Control Studies; D015331:Cohort Studies; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D014202:Tremor / Q000503:physiopathology*
Essential tremor; aging-related tremor; brain stem; cerebellum; coherence; connectivity; source analysis