What are the potential causes of shaking in the left arm and hand when held out straight in an older adult with a history of tremors?

Shaking in Left Arm and Hand When Held Outstretched

The most likely diagnosis is essential tremor, which characteristically presents as a postural and kinetic tremor that is maximal when the hands are outstretched, though in an older adult with tremor history, you must urgently rule out limb-shaking TIA (a rare manifestation of carotid occlusive disease) and consider Parkinson's disease or functional tremor. 1, 2

Immediate Diagnostic Priorities

Critical Red Flags Requiring Urgent Evaluation

• Limb-shaking TIA must be excluded if the tremor is precipitated by postural changes, head turning, or hyperextension of the neck, as this represents critical carotid stenosis requiring urgent vascular imaging 2
• The tremor in limb-shaking TIA is typically 3-4 Hz, rhythmic, and can be mistaken for seizures, but lacks Jacksonian march and is precipitated by maneuvers causing carotid compression 2
• Immediate carotid duplex ultrasound or MRA is indicated if there are any vascular risk factors (hypertension, diabetes, smoking, prior stroke) or if the tremor is triggered by positional changes 2

Distinguishing Features on Examination

Essential Tremor characteristics:

• Kinetic tremor (during movement) is greater than postural tremor (when arm is outstretched) 3
• Wrist flexion-extension tremor predominates over wrist rotation tremor 3
• The tremor is regularly recurrent without directionality 3
• Postural tremors in both arms are typically out of phase 3
• Intention tremor (during finger-nose-finger testing) occurs in 50% of cases 3
• Arm tremor is generally mildly asymmetric, which fits with unilateral left arm presentation 3

Parkinson's Disease features:

• Resting tremor (4-6 Hz) that disappears with movement is the hallmark—this is opposite to the scenario described 4, 1
• If tremor is present when arm is held outstretched but absent at rest, Parkinson's is less likely 1
• However, rest tremor can occur as a late feature in essential tremor, creating diagnostic confusion 3

Functional Tremor considerations:

• Superimposing alternative voluntary rhythms on the tremor can entrain it to stillness in functional tremor 5
• Use the unaffected right limb to dictate a new rhythm (tapping/opening and closing the hand) to test entrainability 5
• Functional tremor often shows variability in frequency and amplitude with distraction 5

Diagnostic Algorithm

Step 1: Vascular Risk Assessment

• Obtain immediate carotid imaging (duplex ultrasound or MRA) if patient has hypertension, diabetes, smoking history, or if tremor is positional 2
• Limb-shaking TIA patients benefit from urgent reperfusion procedures (surgical or radiological) to reduce stroke risk 2

Step 2: Tremor Characterization

• Observe tremor at rest, with arms outstretched (postural), and during finger-nose-finger testing (kinetic/intention) 1, 3
• Action tremor maximal with outstretched hands suggests essential tremor or enhanced physiologic tremor 1
• Document tremor frequency: essential tremor is typically 4-8 Hz 4
• Assess for head tremor, which occurs mainly in women with essential tremor and follows arm tremor 3

Step 3: Neurological Examination

• Check for bradykinesia, rigidity, and gait disturbance suggesting Parkinson's disease 6
• Perform finger-to-nose and heel-to-shin tests to assess for cerebellar dysmetria 7
• Evaluate for nystagmus, ocular motor abnormalities, or ataxia suggesting posterior fossa pathology 7

Step 4: Medication and Metabolic Review

• Review medications for centrally acting agents that could cause or worsen tremor 7
• Consider thyroid function tests, electrolytes, and glucose to exclude metabolic causes 6
• Assess for alcohol use, as withdrawal can cause action tremor 6

Treatment Approach

For Essential Tremor (Most Likely)

• Propranolol is first-line therapy for essential tremor, particularly effective for postural and action tremor 6, 4
• Primidone is an alternative first-line agent 6, 4
• Benzodiazepines can be used but should be avoided in elderly patients due to fall risk and cognitive dysfunction 8, 4

For Parkinson's Disease (If Resting Tremor Present)

• Carbidopa-levodopa combination remains first-line treatment for parkinsonian tremor 9, 6, 4
• Anticholinergics can be effective but are poorly tolerated in older adults 4

For Functional Tremor

• Avoid aids and equipment in the acute phase, as they interrupt normal automatic movement patterns 5
• Teach techniques to superimpose alternative voluntary rhythms to entrain tremor to stillness 5
• Use gross rather than fine movements initially (large marker on whiteboard rather than normal handwriting) 5
• Discourage cocontraction or tensing of muscles as a method to suppress tremor 5

Critical Pitfalls to Avoid

• Do not assume essential tremor without excluding limb-shaking TIA in an older adult with vascular risk factors—this is a stroke-risk emergency 2
• Do not diagnose Parkinson's disease based solely on tremor when outstretched, as this is an action tremor pattern, not the resting tremor of Parkinson's 1
• Do not prescribe levodopa for action tremor—it is ineffective and may worsen the tremor 1
• Avoid prolonged benzodiazepine use in elderly patients due to increased fall risk, cognitive impairment, and drug interactions 8
• Do not overlook medication-induced tremor, particularly from beta-agonists, valproate, lithium, or stimulants 6

Urgent Imaging Indications

MRI brain with diffusion-weighted imaging is indicated if: 7

• New ataxia, dysmetria, or limb incoordination accompanies the tremor
• Vertical diplopia, nystagmus, or ocular motor abnormalities are present
• Associated vertigo, nausea, weakness, sensory changes, or dysarthria occur
• Any red flag features suggesting posterior circulation stroke