From the Guidelines
Tremors are typically associated with disorders affecting the cerebellum, basal ganglia, and peripheral nerves, rather than upper or lower motor neuron disorders. The clinical presentation of tremors can vary depending on the underlying cause, with cerebellar tremors (intention tremors) occurring during voluntary movement and worsening as the limb approaches its target 1. Parkinsonian tremors, associated with basal ganglia dysfunction, are typically resting tremors that decrease with intentional movement 1. Essential tremor, one of the most common movement disorders, involves postural or action tremors and is thought to involve cerebellar-thalamic-cortical circuits 1. Lower motor neuron disorders can sometimes produce fasciculations, which are brief, spontaneous contractions of muscle fibers that may appear tremor-like but are mechanistically different from true tremors 1. Understanding the specific characteristics of a tremor—whether it occurs at rest, during action, or with posture maintenance—helps determine its neuroanatomical origin and guides appropriate treatment. Some key points to consider when evaluating tremors include:
- The presence of resting tremors, which are characteristic of Parkinsonian syndromes 1
- The presence of intention tremors, which are characteristic of cerebellar disorders 1
- The presence of postural or action tremors, which are characteristic of essential tremor 1
- The presence of fasciculations, which are characteristic of lower motor neuron disorders 1. It is essential to note that while upper motor neuron lesions can produce spasticity and rigidity, they are less commonly associated with tremors 1.
From the Research
Tremor Classification
- Tremors can be classified as postural, rest, or action tremors 2
- They can be symptomatic of various disorders, including Parkinson's disease, essential tremor, orthostatic tremor, cerebellar disease, peripheral neuropathy, and alcohol withdrawal 2, 3
Pathophysiology of Tremors
- The pathophysiology of tremors in motor neuron disease may be central rather than peripheral in origin 4
- Action tremor in motor neuron disease can be part of a multisystem neurodegenerative disease and may be due to cerebellar dysfunction 4
- Peripheral neuropathy can also be present in Parkinson's disease, with links to prolonged L-DOPA exposure, homocysteine and methylmalonic acid levels, and genetic mutations 5
Upper or Lower Motor Neuron Involvement
- The study on motor neuron disease suggests that tremor in this condition may be central rather than peripheral in origin, implying upper motor neuron involvement 4
- However, peripheral neuropathy in Parkinson's disease indicates that lower motor neurons can also be affected 5
- The exact classification of tremors as upper or lower motor neuron disorders is not explicitly stated in the provided studies, but the evidence suggests that both can be involved depending on the underlying condition 2, 3, 6, 4, 5