Significant evidence supports the assertion that Essential Tremor (ET) is a progressively degenerative neurodegenerative disorder, with its classification evolving. Research has shown clear pathological changes in the brain, such as Purkinje cell loss and cerebellar abnormalities, which indicate neurodegeneration. ET is also linked to non-motor symptoms like mild cognitive impairments and accelerated cognitive decline, similar to other neurodegenerative conditions.
Essential tremor (ET) belongs to a group of diseases known as neurodegenerative disorders or, more specifically, movement disorders, though it was once considered a more isolated condition.
Evidence suggests that ET is likely a complex and heterogeneous family of conditions rather than a single disease, with some cases showing genetic links to other neurodegenerative or movement disorders.
Evidence suggests that ET is likely a complex and heterogeneous family of conditions rather than a single disease, with some cases showing genetic links to other neurodegenerative or movement disorders.
- Progressive Nature: ET is a chronic, progressive disorder, meaning it worsens over time.
- Neuronal Changes: Studies show that ET is associated with neuronal loss and postmortem changes in specific cell populations within the nervous system, a hallmark of neurodegenerative diseases.
- Selective Vulnerability: The disease shows a selective vulnerability of specific cell populations, leading to cell loss and a decline in function.
- Heterogeneity: While there is debate, many clinical features suggest ET is a degenerative disorder, with differences in age of onset and progression rates among patients.
Why "family of diseases"?
- Heterogeneity: The clinical presentation of essential tremor is diverse, with variations in affected body parts (hands, head, voice, etc.) and the presence of non-motor symptoms.
- Neuropathology: Studies have identified pathological changes in the cerebellum, the part of the brain that controls movement, characteristic of neurodegenerative conditions.
- Genetics: Essential tremor can be inherited in an autosomal dominant pattern, suggesting genetic factors are at play. Research has also identified different genes associated with ET.
- Associated conditions: Some individuals with essential tremor may also have other neurological conditions, such as Parkinson's disease or dementia, or a family history of other movement disorders, like dystonia.
Essential Tremor is a Neurological & Neurodegenerative disease
Evidence for ET as a neurodegenerative disorder:
- Post-mortem studies: These studies have shown neuronal loss, particularly Purkinje cells in the cerebellum, and other cellular changes typical of neurodegenerative diseases.
- Advanced neuroimaging: MRI and other techniques reveal distinct structural changes in the brain, including evidence of neuronal loss, which supports the neurodegenerative hypothesis.
- Association with other neurodegenerative diseases: There is a noted increased risk of developing Parkinson's disease (PD) in individuals with ET.
- Progressive nature: Symptoms of ET typically worsen over time, a hallmark of many progressive neurodegenerative disorders.
- Non-motor symptoms: The presence of cognitive deficits (attention, executive function, memory) and other non-motor features, which can progress, further aligns ET with the broader category of neurodegenerative diseases.
Controversy and alternative views:
- Some researchers still propose that ET might be primarily an "electrical disorder" related to overactivity in motor networks, without necessarily involving significant underlying brain damage.
- There is also the idea that ET might be a complex group of diseases rather than a single entity.
In summary: While the debate continues, the current scientific consensus leans towards essential tremor being a neurodegenerative disorder, given the accumulating evidence of progressive cellular changes in the brain and its association with other neurological conditions.
ET Neurodegenerative Study: Dr. Benito-León is supported by the National Institutes of Health. Monitoring Editor: Elan D. Louis.
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National Library of Medicine
Evidence
*Associated non-motor features
-Suggests more widespread involvement of different functional brain regions
*Cognitive deficits
-Increased prevalence or incidence of MCI and dementia in ET
*Psychiatric features (depression, anxiety, social phobia)
-Many neurodegenerative diseases are neuropsychiatric disorders. Depression in ET may be primary
*Mild olfactory dysfunction, hearing impairment, sleep dysregulation
-Increased in some ET patients. Not specific to neurodegeneration
- Insidious onset
- Prevalence increases with age, and exponentially with advanced age
- Older age of onset associated with more rapid disease progression
- Somatotopic spread of tremor to cranium (neck, voice, jaw) with disease progression
- Intention tremor, gait ataxia, oculomotor abnormalities
- Isolated rest tremor in arm only with longstanding disease
*Associated non-motor features
-Suggests more widespread involvement of different functional brain regions
*Cognitive deficits
-Increased prevalence or incidence of MCI and dementia in ET
*Psychiatric features (depression, anxiety, social phobia)
-Many neurodegenerative diseases are neuropsychiatric disorders. Depression in ET may be primary
*Mild olfactory dysfunction, hearing impairment, sleep dysregulation
-Increased in some ET patients. Not specific to neurodegeneration
- Increased risk of AD
- Increased risk of PD
- Hereditability factors lead to earlier onset disease
