What is the cause of sudden onset dizziness and fatigue in a previously healthy individual?

Sudden Dizziness and Fatigue in a Previously Healthy Individual

In a previously healthy individual with sudden onset dizziness and fatigue, the most critical priority is to immediately rule out life-threatening cardiac and neurological causes—specifically cardiac arrhythmias (particularly atrioventricular block), posterior circulation stroke, and orthostatic hypotension—before considering benign peripheral vestibular disorders.

Immediate Life-Threatening Causes to Exclude

Cardiac Arrhythmias

• Atrioventricular block can present with fatigue and dizziness, particularly when conducting in a 2:1 pattern or occurring during exertion 1
• Second-degree AV block type I (Wenckebach), while often asymptomatic in healthy patients, can cause exertional intolerance or dizziness when occurring frequently or during exercise 1
• Intermittent complete AV block causing presyncope can occur even in patients with no baseline heart disease or evident conduction abnormalities, with 8% of syncope patients having paroxysmal idiopathic AV block despite normal ECG and echocardiogram 1
• Obtain an immediate 12-lead ECG to assess for conduction abnormalities, bradycardia, or prolonged PR interval (>300 ms can cause "pseudo pacemaker syndrome") 1

Posterior Circulation Stroke

• Acute persistent vertigo with dizziness lasting days to weeks requires differentiation between peripheral vestibular causes and stroke, as 75-80% of patients with posterior circulation infarct have no focal neurologic deficits 2, 3
• Isolated transient vertigo may precede a vertebrobasilar stroke by weeks or months, with attacks typically lasting less than 30 minutes 1
• Perform the HINTS examination (Head-Impulse, Nystagmus, Test of Skew) if trained, which has 100% sensitivity for detecting stroke versus 46% for early MRI 2, 4
• Red flags requiring urgent MRI brain without contrast include: sudden severe headache, focal neurological deficits, inability to stand or walk, downbeating nystagmus, or sudden unilateral hearing loss 2, 3

Orthostatic Hypotension and Autonomic Dysfunction

• Orthostatic hypotension presents with dizziness, fatigue, weakness, and lethargy upon standing due to impaired sympathetic vasoconstriction 1
• Classical orthostatic hypotension occurs 30 seconds to 3 minutes after standing and is commonly drug-induced (vasoactive drugs, diuretics, alpha-blockers) or related to volume depletion 1
• Measure orthostatic vital signs: blood pressure and heart rate supine, then at 1 and 3 minutes after standing 1
• A systolic BP drop ≥20 mmHg or diastolic drop ≥10 mmHg confirms orthostatic hypotension 1

Secondary Considerations After Excluding Life-Threatening Causes

Benign Paroxysmal Positional Vertigo (BPPV)

• Brief episodic vertigo lasting seconds to <1 minute triggered by head position changes suggests BPPV 2, 3
• Perform the Dix-Hallpike maneuver as the gold standard diagnostic test, looking for latency of 5-20 seconds, torsional upbeating nystagmus toward the affected ear, and symptoms resolving within 60 seconds 2, 4
• BPPV does not typically cause isolated fatigue without positional vertigo 2

Vestibular Neuritis

• Acute persistent vertigo with constant symptoms, nausea, and vomiting lasting days suggests vestibular neuritis 3
• Fatigue may accompany the acute phase but is not the predominant symptom 3

Medication-Induced Causes

• Review all medications, as antihypertensives, sedatives, anticonvulsants, psychotropic drugs, and cardiovascular medications commonly cause dizziness and fatigue 1, 2
• Drug-induced atrial fibrillation can present with fatigue, palpitations, dizziness, and shortness of breath 1

Infectious and Inflammatory Causes

• Lyme carditis causes AV block (usually at the AV nodal level) with approximately 40% requiring temporary pacing, though permanent block after antibiotic therapy is rare 1
• COVID-19 can present with anosmia, dizziness, and fatigue as early symptoms 1

Anemia and Metabolic Causes

• Chronic gastrointestinal bleeding from small intestinal ulcers can present with recurrent dizziness, fatigue, and anemia over years 5
• Check complete blood count, basic metabolic panel, and glucose to exclude anemia, electrolyte abnormalities, and hypoglycemia 1

Diagnostic Algorithm

1. Obtain vital signs including orthostatic measurements and 12-lead ECG immediately 1
2. Perform focused neurological examination looking for focal deficits, ataxia, and abnormal nystagmus patterns 2, 3
3. If acute persistent vertigo with high vascular risk factors (age >50, hypertension, diabetes, prior stroke), obtain MRI brain without contrast even with normal neurologic exam, as 11-25% may have posterior circulation stroke 2
4. If brief episodic positional symptoms, perform Dix-Hallpike maneuver 2, 4
5. Review medication list for causative agents 1, 2
6. Obtain basic laboratory studies: CBC, BMP, glucose 1

Critical Pitfalls to Avoid

• Do not rely on the patient's description of "spinning" versus "lightheadedness"—instead focus on timing (seconds, minutes, hours, days) and specific triggers (positional, spontaneous, exertional) 2, 3
• Do not assume a normal neurologic examination excludes stroke, as most posterior circulation strokes present without focal deficits 2, 3
• Do not order CT head for isolated dizziness, as it has <1% diagnostic yield and misses most posterior circulation infarcts; MRI with diffusion-weighted imaging is far superior (4% vs <1% yield) 2
• Do not overlook reversible causes such as Lyme carditis or drug toxicity, which require medical therapy and supportive care before determining need for permanent pacing 1
• Do not skip orthostatic vital signs, as medication-induced orthostatic hypotension is a leading reversible cause of dizziness and fatigue 1, 2

When Imaging IS Indicated

• Abnormal neurologic examination 2
• HINTS examination suggesting central cause 2
• High vascular risk patients (age >50, hypertension, diabetes, atrial fibrillation, prior stroke) with acute vestibular syndrome 2
• Sudden unilateral hearing loss 2, 3
• New severe headache 2
• Progressive neurologic symptoms 2
• Unilateral or pulsatile tinnitus 2

When Imaging is NOT Indicated

• Brief episodic vertigo with positive Dix-Hallpike test consistent with BPPV and no red flags 2, 4
• Acute persistent vertigo with normal neurologic exam and HINTS examination consistent with peripheral vertigo by trained examiner 2
• Nonspecific dizziness without vertigo, ataxia, or neurologic deficits 2