What is the differential diagnosis for a patient presenting with lightheadedness, syncope, and shakiness?

Differential Diagnosis for Lightheadedness, Syncope, and Shakiness

The most common causes of this symptom triad are orthostatic intolerance (including orthostatic hypotension and postural orthostatic tachycardia syndrome), reflex (vasovagal) syncope, cardiac arrhythmias, and medication side effects—with the specific diagnosis determined by timing of symptoms, positional triggers, and associated features. 1, 2

Immediate Diagnostic Framework

The key to narrowing your differential is determining when symptoms occur and what triggers them, rather than focusing solely on the patient's description of the sensation 2:

Position-Triggered Causes

Orthostatic hypotension presents with lightheadedness occurring within 3 minutes of standing from sitting or lying, defined as a sustained drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg 1. The shakiness in this context represents the sympathetic nervous system's attempt to compensate for inadequate cerebral perfusion 2.

• Delayed orthostatic hypotension takes >3 minutes to develop and is frequently missed if you only measure standing vitals for 1-2 minutes—you must check BP at 1,3,5, and 10 minutes of standing 1, 2
• Neurogenic orthostatic hypotension is a subtype caused by autonomic nervous system dysfunction rather than environmental triggers like dehydration or medications 1

Postural orthostatic tachycardia syndrome (POTS) causes lightheadedness with a sustained heart rate increase ≥30 bpm within 10 minutes of standing (≥40 bpm in ages 12-19) without significant BP drop 1, 2. The shakiness represents tremulousness from excessive sympathetic activation 1.

Reflex (Vasovagal) Syncope

Reflex syncope (also called neurally-mediated or vasovagal syncope) is the most frequent cause of transient loss of consciousness and presents with prodromal symptoms including lightheadedness, visual changes ("tunnel vision" or "graying out"), sweating, nausea, and shakiness before syncope occurs 1, 3. This represents an inappropriate reflex by an otherwise normal autonomic nervous system, fundamentally different from autonomic failure 1.

• Prodromal symptoms are related to both decreased cerebral blood flow (lightheadedness, visual changes) and the mechanism causing syncope (sweating, nausea) 1
• The shakiness may represent tremulousness from sympathetic activation before the parasympathetic surge that causes syncope 1

Cardiac Causes

Cardiac arrhythmias (both bradycardia and tachycardia) cause lightheadedness and syncope through inadequate cardiac output and cerebral hypoperfusion 1. The shakiness may represent palpitations or tremulousness from catecholamine release 1.

• Ventricular tachycardia, heart block, and sick sinus syndrome are high-risk causes requiring urgent evaluation 1
• Structural heart disease (aortic stenosis, hypertrophic cardiomyopathy) can cause exertional syncope 1

Medication-Induced

Medication side effects, particularly from diuretics, vasodilators, antihypertensives, and sedatives, commonly cause chronic lightheadedness and orthostatic symptoms 2. This is especially prevalent in older patients 2.

Critical Red Flags Requiring Urgent Evaluation

You must identify patients with serious conditions that require immediate inpatient evaluation 1:

• Syncope during exertion or while supine (suggests cardiac cause) 1
• Chest pain, dyspnea, or palpitations (suggests cardiac arrhythmia or structural disease) 1
• New neurological deficits (suggests vertebrobasilar insufficiency or posterior circulation stroke/TIA) 2
• Family history of sudden cardiac death or inherited arrhythmia syndromes 1
• Abnormal ECG showing conduction disease, ischemia, or arrhythmia 1

Essential Physical Examination

Measure orthostatic vital signs by checking BP and heart rate supine, then at 1,3,5, and 10 minutes of standing to capture delayed orthostatic hypotension 2. Document any symptoms that occur during the standing test 2.

• A heart rate increase ≥15 bpm upon standing indicates appropriate autonomic compensation 4
• Look for associated symptoms during standing: lightheadedness, palpitations, tremor, weakness, visual disturbances 2

Additional Differential Considerations

Metabolic causes including hypoglycemia, anemia, and dehydration can present with this symptom triad 2. The shakiness may represent hypoglycemia-induced tremor or weakness from anemia 2.

Anxiety and panic disorders frequently cause lightheadedness, tremulousness, and near-syncope, though true loss of consciousness is rare 2. Note that hyperventilation symptoms fall under "panic attacks" in psychiatric classification, and it remains uncertain whether hyperventilation alone can cause true loss of consciousness 1.

Common Pitfalls to Avoid

• Don't dismiss orthostatic symptoms as "just dehydration" or anxiety without proper orthostatic vital sign measurement 2
• Don't confuse presyncope (near-syncope) with true syncope—presyncope includes extreme lightheadedness and variable degrees of altered consciousness without complete loss of consciousness 1
• Don't use vague terms like "dysautonomia" without specifying the nature of autonomic dysfunction (autonomic failure versus reflex syncope are fundamentally different) 1
• Don't assume all shakiness is seizure activity—it may represent tremulousness from sympathetic activation or muscle weakness from hypoperfusion 1, 2