What exams should be done for a patient with dizziness, suspected to be caused by Hydrochlorothiazide (HCTZ), and a differential diagnosis of vertigo, in the context of a history of hypertension?

Diagnostic Examination for Dizziness with Suspected HCTZ Etiology and Vertigo Differential

Initial Clinical Assessment

Begin with orthostatic blood pressure measurement and a focused neurologic examination to distinguish medication-induced presyncope from true vertigo, as HCTZ commonly causes orthostatic hypotension through volume depletion and electrolyte disturbances. 1

Orthostatic Vital Signs

• Measure blood pressure and heart rate supine, then after 1 and 3 minutes of standing 2, 3
• A drop of ≥20 mmHg systolic or ≥10 mmHg diastolic suggests volume depletion from HCTZ 3, 4
• HCTZ-induced dizziness typically manifests as presyncope occurring after standing, particularly after recent dose increases 1

Electrolyte Assessment

• Check serum electrolytes (sodium, potassium, magnesium) immediately, as HCTZ-induced hypokalemia and hyponatremia can cause dizziness, weakness, and lethargy that patients may describe as "dizziness." 1
• Warning signs of electrolyte imbalance include weakness, lethargy, drowsiness, muscle cramps, and fatigue 1

Distinguishing Peripheral Vertigo from Medication Effects

Dix-Hallpike Maneuver

• Perform the Dix-Hallpike maneuver bilaterally to diagnose or exclude benign paroxysmal positional vertigo (BPPV), the most common cause of peripheral vertigo (42% of cases). 5, 6
• Positive findings include: torsional and upbeating nystagmus with 5-20 second latency, crescendo-decrescendo pattern, fatigability with repeat testing, and resolution within 60 seconds 6
• If the Dix-Hallpike is positive with typical nystagmus, imaging is unnecessary. 5
• Atypical findings (immediate onset, persistent nystagmus, purely vertical without torsional component) suggest central pathology requiring urgent neuroimaging 5, 6

Nystagmus Examination

• Assess for spontaneous nystagmus at baseline without provocative maneuvers 6
• Peripheral vertigo produces horizontal nystagmus with rotatory component, unidirectional, suppressed by visual fixation, and fatigable 6
• Central vertigo produces pure vertical nystagmus, direction-changing, not suppressed by visual fixation 6
• Baseline nystagmus without provocative maneuvers is a red flag for central causes. 6

Neurologic Examination for Central Causes

HINTS Examination (if acute vestibular syndrome present)

• Perform head-impulse test, assess nystagmus pattern, and test of skew deviation 3, 4
• This examination distinguishes peripheral from central etiologies when vertigo is continuous and severe 3

Assess for Neurologic Deficits

• Examine for dysarthria, dysmetria, dysphagia, sensory or motor deficits, diplopia, limb weakness, truncal/gait ataxia, or Horner's syndrome—any of these mandate immediate neuroimaging. 6
• Test gait and balance: severe postural instability with falling suggests central pathology (vertebrobasilar insufficiency or cerebellar lesions) 6
• Approximately 10% of cerebellar strokes present similarly to peripheral vestibular disorders. 6

Timing and Trigger Assessment

Episode Characteristics

• Episodes lasting <1 minute triggered by head position changes suggest BPPV 6
• Episodes lasting hours with hearing loss, tinnitus, and aural fullness suggest Ménière disease 7, 6
• Episodes lasting <30 minutes without hearing loss suggest vertebrobasilar insufficiency 6
• Daily continuous dizziness without true spinning vertigo is more consistent with medication side effects, anxiety, or cervicogenic causes 7

Hearing Evaluation

• Perform Weber and Rinne tests 6
• An abnormal Weber test mandates formal audiometry to characterize hearing loss type and degree. 6
• Fluctuating hearing loss distinguishes Ménière disease from other causes 6

Laboratory Testing

Essential Tests

• Serum electrolytes (sodium, potassium, magnesium, chloride) 1
• Blood glucose (HCTZ can cause hyperglycemia) 1
• Renal function (creatinine, BUN) as HCTZ elimination is prolonged in renal disease 1

When NOT to Order Tests

• Routine neuroimaging is not indicated for typical BPPV with positive Dix-Hallpike and no red flags. 5, 6
• The diagnostic yield of CT in isolated dizziness is <1%; MRI is 4% 5, 7
• Laboratory testing beyond electrolytes is rarely helpful in acute dizziness evaluation 2, 3

Red Flags Requiring Urgent Neuroimaging

Any of the following demand immediate MRI brain with diffusion-weighted imaging: 5, 6

• Severe postural instability with falling
• New-onset severe headache with vertigo
• Any additional neurologic symptoms (dysarthria, diplopia, weakness, sensory deficits)
• Downbeating nystagmus on Dix-Hallpike without torsional component
• Failure to respond to appropriate peripheral vertigo treatments
• Purely vertical nystagmus without torsional component
• Baseline nystagmus present without provocative maneuvers

Common Pitfalls to Avoid

• Do not assume dizziness in a hypertensive patient on HCTZ is due to elevated blood pressure—it is more likely due to medication-induced hypotension, electrolyte disturbances, or unrelated vestibular disease. 8
• Do not overlook subtle neurologic signs that may indicate central pathology 6
• Do not prescribe vestibular suppressants for BPPV as they prevent central compensation 6
• Do not miss the 10% of cerebellar strokes that present identically to peripheral vestibular disorders 6
• Approximately 25% of patients with acute vestibular syndrome have cerebrovascular disease, rising to 75% in high vascular risk cohorts. 6