A tremor is an involuntary, rhythmic, oscillatory movement of a body part. These movements result from the alternating or simultaneous contraction of opposing muscles. Tremors are classified based on the circumstances under which they occur, such as when a muscle is at complete rest or when it is active. Postural tremor is a specific type of action tremor that manifests when a person actively holds a body part in a position against gravity. This article explains the mechanics, primary causes, and general steps for diagnosis and management of postural tremor.
Defining Postural Tremor: When and How It Occurs
Postural tremor is characterized by shaking that begins when a person maintains a voluntary posture. This occurs when a limb is held stationary against gravity, such as holding the arms outstretched or holding a cup steady. The tremor typically ceases immediately when the limb is fully relaxed and supported, or when the person moves the limb to perform an action. This places it within the broader category of action tremors, which are linked to muscle activation.
Postural tremor must be distinguished from other involuntary movements. A resting tremor, often associated with Parkinson’s disease, occurs when the muscle is completely relaxed and diminishes during voluntary movement. An intention tremor is absent at rest and during posture, but intensifies as the limb moves closer to its target. The defining characteristic of postural tremor is its presence during the maintenance of a fixed, non-moving position.
The frequency of a postural tremor usually falls within the range of 4 to 12 Hertz, meaning the limb oscillates 4 to 12 times per second. This rhythmic oscillation results from abnormal signaling within the central nervous system affecting motor control circuits. While often most noticeable in the hands and arms, the involuntary movement can also affect the head, voice, legs, and trunk when those parts are actively held in position.
The Primary Causes of Postural Tremor
Postural tremor generally stems from two main categories: a long-term neurological condition or a temporary, reversible state. The most common cause overall is Enhanced Physiological Tremor (EPT), which is a temporary amplification of the minimal, natural tremor everyone experiences. EPT results from increased sympathetic nervous system activity, which heightens the body’s “fight or flight” response.
This enhanced state can be triggered by external or metabolic factors, including acute anxiety, emotional stress, physical exhaustion, or the consumption of stimulants like caffeine. Certain medications, such as antidepressants and thyroid replacement hormones, can also elevate sympathetic activity and induce EPT. The tremor is typically fine, symmetrical, and has a higher frequency, often between 7 and 12 Hertz. Since EPT is triggered by an identifiable factor, it is generally reversible once the underlying cause is addressed.
The most common neurological cause of persistent postural tremor is Essential Tremor (ET). ET is a progressive disorder that often involves a genetic component. It is characterized by a tremor that is both postural and kinetic, meaning it is present when holding a position and when moving. It typically affects both sides of the body, often beginning in the hands and sometimes progressing to the head, voice, or legs.
Essential Tremor is thought to be related to abnormal communication between the cerebellum and other areas of the brain. The frequency of ET is typically lower than EPT, usually ranging from 4 to 8 Hertz. While the exact cause remains unclear, a family history suggests an inherited component in about half of the cases, and it is a chronic condition that may gradually worsen.
How Doctors Identify and Address Postural Tremor
Identifying the cause of a postural tremor begins with a detailed medical history and a physical examination. The doctor will ask about the onset and frequency of the shaking, whether it is relieved by rest or exacerbated by stress, and if there is a family history of tremor. A thorough review of all medications and lifestyle factors, such as caffeine and alcohol intake, is performed to screen for drug-induced or enhanced physiological causes.
During the neurological examination, the physician observes the tremor while the patient performs specific tasks designed to activate it, such as holding the arms outstretched. They may also ask the patient to perform kinetic tasks like drawing a spiral to assess how the tremor affects movement. Blood tests may be ordered to rule out metabolic conditions that can cause tremor, such as an overactive thyroid gland or liver disorders.
Management strategies for postural tremor are highly specific to the underlying cause. If the tremor is Enhanced Physiological Tremor, the primary approach is to remove the trigger. This involves reducing caffeine intake, managing anxiety, or adjusting the dosage of a triggering medication in consultation with the prescribing physician.
For Essential Tremor, treatment focuses on reducing the severity of the tremor to improve daily function. Medication options often include beta-blockers, such as propranolol, and certain anti-seizure drugs, such as primidone. While these medications are not a cure, they can significantly suppress the involuntary movements. For severe, disabling ET where medication is ineffective, surgical options like deep brain stimulation may be considered.