In a 40-year-old woman with hypothyroidism on levothyroxine 112 µg, who has had a one-week history of recurrent dizziness (mostly in the morning), a single syncopal episode, right‑ear tinnitus, and increased stress/anxiety, what is the appropriate workup and most likely diagnosis?

Workup and Diagnosis

This patient requires urgent evaluation for cardiac causes of syncope first, followed by assessment for vestibular disorders, with particular attention to excluding levothyroxine overtreatment as a contributor to her symptoms.

Immediate Priority: Rule Out Life-Threatening Cardiac Causes

The syncopal episode is the most concerning feature and demands immediate attention. Loss of consciousness is never a symptom of Ménière's disease 1, which immediately shifts the differential away from purely vestibular etiologies and toward cardiac or neurologic causes.

Essential Initial Workup:

Cardiac evaluation (highest priority):

• 12-lead ECG - to assess for arrhythmias, conduction abnormalities
• Orthostatic vital signs - measure blood pressure and heart rate supine and after 3 minutes standing
• Thyroid function tests (TSH, free T4) - critical given levothyroxine therapy
• Continuous cardiac monitoring (Holter or event monitor) - given recurrent symptoms 2

Rationale: Levothyroxine overtreatment can precipitate cardiac arrhythmias, tachycardia, and palpitations 3. The FDA label explicitly warns that overtreatment may cause "arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest" 3. Conversely, severe hypothyroidism can cause bradyarrhythmias and syncope 4.

Secondary Assessment: Vestibular vs. Other Causes

Key Clinical Distinctions to Clarify:

Characterize the "dizziness":

• True vertigo (spinning sensation) vs. lightheadedness/presyncope (feeling faint)
• This distinction is critical: lightheadedness suggests cardiovascular causes (orthostatic hypotension, vasovagal syncope, arrhythmia), while true vertigo suggests vestibular pathology 1

Morning timing pattern suggests:

• Orthostatic hypotension (common with rapid position changes upon waking)
• Possible levothyroxine-induced cardiac effects
• Less consistent with typical Ménière's disease (attacks are spontaneous, not time-related)

Differential Diagnosis Framework:

1. Levothyroxine-Related (Most Likely Given Context):

• Overtreatment: Can cause arrhythmias, palpitations, anxiety symptoms 3
• Undertreatment: Can cause bradycardia and syncope 4
• TSH and free T4 levels will guide this assessment

2. Vestibular Migraine (Consider if true vertigo present):

• Attacks typically last hours (can be minutes to >24 hours) 1
• Associated with stress/anxiety (patient reports significant recent stress)
• Tinnitus can occur but hearing loss is less common than in Ménière's
• Clinicians should assess for vestibular migraine when evaluating for Ménière's disease 1

3. Ménière's Disease (Less Likely):

• Requires unilateral tinnitus (patient has right ear involvement - consistent)
• Requires fluctuating hearing loss (not mentioned in history)
• Requires episodic vertigo lasting 20 minutes to 12 hours (duration unclear here)
• Syncope excludes this diagnosis 1

4. Vasovagal Syncope:

• Single episode with stress/anxiety context 2
• Would not explain tinnitus or morning dizziness pattern

5. Benign Paroxysmal Positional Vertigo (BPPV):

• Positional vertigo lasting seconds, not minutes/hours
• No associated tinnitus or syncope 1

Complete Workup Algorithm:

Tier 1 (Urgent - within 24-48 hours):

• ECG
• Orthostatic vital signs
• TSH, free T4
• Complete blood count, comprehensive metabolic panel
• Cardiac monitoring if ECG abnormal or high suspicion

Tier 2 (If cardiac workup negative):

• Audiometry - essential to document hearing loss if present (required for Ménière's diagnosis)
• Detailed vestibular history - duration of episodes, triggers, associated symptoms
• Consider tympanometry (hypothyroidism can affect Eustachian tube function 5)

Tier 3 (Specialist referral if indicated):

• ENT/Audiology if hearing loss or definite vertigo confirmed
• Cardiology if arrhythmia or structural heart disease identified
• Neurology if atypical features or concern for central causes

Critical Pitfalls to Avoid:

1. Do not assume vestibular pathology without ruling out cardiac causes - syncope demands cardiac evaluation first
2. Do not overlook levothyroxine dose optimization - both over- and undertreatment can cause these symptoms 3
3. Do not diagnose Ménière's without documented fluctuating hearing loss - this is a required criterion 1
4. Do not miss the stress/anxiety component - this increases likelihood of vestibular migraine or vasovagal syncope 1, 2

Most Likely Diagnosis:

Based on the clinical presentation, the most probable diagnosis is either:

1. Levothyroxine-induced cardiac effects (over- or undertreatment) with orthostatic component
2. Vestibular migraine triggered by stress, IF true vertigo is confirmed
3. Vasovagal syncope with concurrent benign tinnitus

The TSH/free T4 results will be decisive in determining next steps. If thyroid function is abnormal, adjust levothyroxine and reassess. If thyroid function is optimal and cardiac workup is negative, proceed with vestibular evaluation and consider vestibular migraine as primary diagnosis given the stress context and tinnitus 1, 6.