Introduction
Heilman described primary orthostatic tremors for the first time in 1984. The medical literature is divided on whether primary orthostatic tremor is a type of essential tremor, a separate clinical entity, or an exaggerated physiological response to standing still. Females are affected slightly more frequently than males. Because many people with primary orthostatic tremors go unrecognized or misdiagnosed, some believe the disorder is underdiagnosed, making it difficult to determine the true prevalence of this disease in the general population.
What Is Primary Orthostatic Tremor?
Orthostatic tremor (OT) is a rare neurological condition characterized by standing-related rhythmic tremors in the legs and trunk. Primary orthostatic tremor (POT) is a type of OT that occurs without another neurological or systemic disorder. Although the precise prevalence of POT is unknown, it is considered a rare condition. It is a progressive movement disorder characterized by unsteadiness while standing due to a rapid tremor affecting the legs and trunk. The tremor is sometimes described as 'shaky legs,' it improves when walking, sitting, or lying down. For this reason, people with primary orthostatic tremors fear falling and may attempt to sit or walk immediately after standing. Tiredness, physical exhaustion, pain, and muscle stiffness or weakness are all symptoms of POT.
What Are the Signs and Symptoms of Primary Orthostatic Tremors?
The most common symptom of primary orthostatic tremor is the occurrence of a high-frequency tremor affecting both legs while standing. The tremor is involuntary and rhythmic and causes feelings of vibration, unsteadiness, or imbalance in the legs. It is usually too rapid to be visible to the naked eye. Still, it can be palpated by touching the thighs or calves, listening to these muscles with a stethoscope, or using electromyography.
The tremor associated with POT is position-specific, which means it only occurs when a person is standing and disappears completely or partially when they walk, sit, or lie down. Some people can stand for several minutes before the tremor begins, while others can only stand for a few seconds. The tremor becomes more severe as the condition progresses, as do feelings of unsteadiness. In rare cases, affected people may experience leg stiffness, weakness, or pain.
Although the tremor caused by POT is typically limited to the legs, some affected individuals may also experience arm tremors. In addition, overgrowth of the affected muscles (muscular hypertrophy) may occur in some rare cases in conjunction with primary orthostatic tremors.
It is important to note that POT does not progress to other conditions or affect other body systems. However, the condition can significantly impact an individual's quality of life, especially if it interferes with their ability to stand, walk, or perform daily activities.
What Causes Primary Orthostatic Tremors?
Primary orthostatic tremor has no known cause and is classified as idiopathic. Some researchers believe the disorder is a variant or subtype of essential tremor, while others believe it is a distinct entity on its own.
Primary orthostatic tremors may have a genetic component in some cases, as some affected individuals have a family history of tremors. More research, however, is required to determine the precise role that genetic factors may play in the development of the condition.
Other factors that may contribute to the development of primary orthostatic tremors include abnormal brain activity, changes in the levels of certain neurotransmitters, and disruptions in the nervous system's normal functioning. These theories, however, are still speculative, and more research is needed to fully understand their relevance to the development of primary orthostatic tremors.
How Is Primary Orthostatic Tremor Diagnosed?
POT diagnosis is frequently complex and may necessitate the expertise of a neurologist or movement disorder specialist. There are no definitive diagnostic criteria for POT, so the diagnosis is commonly made based on the patient's clinical history and examination findings.
The presence of a rapid tremor when standing that disappears when sitting or lying down is one of the distinguishing features of POT. The tremor is usually too fast to see with the naked eye and is best detected with surface electromyography (EMG). The electrical impulses of muscle fibers at rest and during contraction are measured by a surface EMG. By reproducing the characteristic tremor in the legs, a surface electromyogram can often quickly establish a diagnosis of primary orthostatic tremor. Surface electromyograms use electrodes placed on the skin overlying the muscles to be tested. EMG can also assist in distinguishing POT from other types of tremors, such as essential tremors, Parkinson's disease, or dystonia.
Other tests that may be used to diagnose POT, in addition to EMG, include:
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Posturography measures a patient's ability to maintain balance.
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Tilt-table testing assesses changes in blood pressure and heart rate when standing.
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Magnetic resonance imaging (MRI) or computed tomography (CT) scans can also rule out other underlying neurological or systemic conditions.
How Is Primary Orthostatic Tremor Treated?
There is currently no cure for POT, and treatment options are limited. However, some management strategies may help patients with POT alleviate symptoms and improve their quality of life.
Pharmacotherapy: Although limited evidence supports its efficacy, pharmacotherapy is frequently used as the first-line treatment for POT. Benzodiazepines such as Clonazepam, anticonvulsants such as Gabapentin or Pregabalin, and beta-blockers such as Propranolol may be used to treat POT. These medications may help some patients reduce tremors and improve balance but may also cause sedation or other side effects.
Botulinum Toxin Injections: Although there is limited evidence to support their use, botulinum toxin injections may also be used to treat POT. Botulinum toxin is a neurotoxin that can be injected directly into muscles to reduce tremors and improve function. The injections are usually given every three to four months and may cause temporary weakness or other side effects.
Deep Brain Stimulation: Deep brain stimulation (DBS) is a surgical procedure in which a device implanted in the brain delivers electrical stimulation to specific areas. DBS has been used successfully in the treatment of other types of tremors, such as essential tremors and Parkinson's disease, and it may also be effective in the treatment of POT. However, no randomized controlled trials are currently available to support the use of DBS.
Conclusion
Primary orthostatic tremor (POT) is a rare neurological condition characterized by a tremor in the legs while standing. It is frequently misdiagnosed, making it difficult to determine its prevalence in the general population. The condition is position-specific, manifesting when standing and disappearing entirely or partially when walking, sitting, or lying down. While no known cause exists, some theories propose abnormal brain activity, genetic factors, and nervous system disruptions. Although there is no cure, pharmacotherapy, physical therapy, and deep brain stimulation may help relieve symptoms.
