How should I evaluate and manage a 51-year-old woman presenting with acute nausea, generalized myalgia, chills, near-syncope with diaphoresis, vomiting, severe fatigue, decreased oral intake, epigastric pain/heartburn, and constipation, who has been off levothyroxine (Synthroid) for three months?

Immediate Management of Acute GI Symptoms with Near-Syncope and Untreated Hypothyroidism

This patient requires urgent thyroid function testing (TSH and free T4), basic metabolic panel, ECG, and orthostatic vital signs, followed by immediate reinitiation of levothyroxine replacement therapy while simultaneously treating her acute vasovagal episode and gastroparesis-like symptoms.

Critical Initial Assessment

Syncope Evaluation

• The near-syncope episode with nausea, diaphoresis, and rapid recovery is consistent with vasovagal syncope, which is characterized by diaphoresis, warmth, nausea, pallor, and is often followed by fatigue 1.
• Perform orthostatic vital signs immediately: measure blood pressure and heart rate supine, then after standing for 3 minutes to assess for orthostatic hypotension (drop ≥20 mmHg systolic or ≥10 mmHg diastolic) 1.
• Obtain a 12-lead ECG to exclude cardiac causes, particularly given her age and acute presentation 1.
• The severe fatigue and "zero energy" combined with the syncopal episode warrants evaluation for metabolic causes including hypothyroidism 1.

Hypothyroidism as Primary Driver

• Untreated hypothyroidism for 3 months is likely the underlying cause of her constellation of symptoms: fatigue (present in 68-83% of hypothyroid patients), myalgias, constipation, and decreased energy 2, 3.
• Hypothyroidism can cause gastroparesis and delayed gastric emptying, explaining her nausea, decreased oral intake, and epigastric symptoms 4.
• The patient's own observation that she had "more energy and less fatigue and muscle aches" on Synthroid confirms symptomatic hypothyroidism 2.

Essential Laboratory Testing

Immediate Blood Work

• TSH and free T4 to confirm hypothyroidism and determine severity 2, 3.
• Comprehensive metabolic panel to assess for hyponatremia, hypercalcemia, hyperglycemia, or renal dysfunction—all metabolic causes of nausea and potential contributors to syncope 1, 5, 6.
• Complete blood count to exclude infection or anemia 6.
• Consider lipase if epigastric pain suggests pancreatitis 6.

Red Flags to Assess

• Check for signs of myxedema coma (hypothermia, hypotension, altered mental status), though unlikely given she is ambulatory 2.
• Assess hydration status given 2 days of decreased oral intake 1.

Thyroid Hormone Replacement

Levothyroxine Initiation

• Start levothyroxine 1.5 to 1.8 mcg/kg/day for this 51-year-old woman without known cardiac disease 3.
• If she has any cardiac risk factors or symptoms, start at a lower dose (25-50 mcg daily) and titrate up 3.
• Recheck TSH and free T4 in 6-8 weeks after initiation, then adjust dose to normalize TSH 2, 3.
• Expect gradual symptom improvement over weeks to months, not immediate resolution; fatigue, myalgias, and constipation should improve as thyroid levels normalize 2.

Management of Acute GI Symptoms

Nausea and Epigastric Pain

• Start metoclopramide 10-20 mg three times daily before meals as first-line therapy for gastroparesis-like symptoms with nausea 1, 5, 4.
• Add a proton pump inhibitor (e.g., omeprazole 20-40 mg daily) for epigastric pain and heartburn symptoms 1, 5.
• If nausea persists despite metoclopramide, add prochlorperazine 5-10 mg every 6-8 hours or ondansetron 4-8 mg every 8 hours 1, 5, 4.
• Use scheduled dosing rather than as-needed for the first week if symptoms are persistent 5.

Constipation Management

• Address constipation aggressively as it is a common cause of nausea and is worsened by hypothyroidism 1, 4.
• Start a stimulant laxative (senna or bisacodyl) plus a stool softener (docusate) 1.
• Consider polyethylene glycol 17 grams daily for maintenance 1.

Dietary Modifications

• Recommend small, frequent meals (5-6 per day) rather than 3 large meals to reduce gastric distension 4.
• Encourage adequate hydration throughout the day, aiming for at least 1.5-2 liters daily 4.
• Avoid trigger foods that worsen symptoms 7.

Syncope Prevention

Vasovagal Precautions

• Educate on prodromal symptoms (nausea, diaphoresis, lightheadedness) and instruct to sit or lie down immediately when these occur 1.
• Increase fluid and salt intake to maintain intravascular volume, particularly given her decreased oral intake 1.
• Avoid prolonged standing, hot environments, and rapid position changes 1.

Orthostatic Hypotension Management (if present)

• If orthostatic hypotension is confirmed, increase fluid intake to 2-3 liters daily and liberalize salt intake 1.
• Consider compression stockings if symptoms persist 1.
• Review for any medications that could contribute (though she reports being off thyroid medication only) 1.

Follow-Up and Monitoring

Short-Term (1-2 Weeks)

• Reassess symptoms, particularly energy level, nausea, and constipation 7.
• Ensure adequate hydration and nutrition 7.
• Monitor for recurrent syncope or worsening symptoms 1.

Medium-Term (6-8 Weeks)

• Recheck TSH and free T4 to assess levothyroxine dosing 2, 3.
• If GI symptoms persist despite normalized thyroid function, consider gastric emptying scintigraphy (4-hour study) to formally diagnose gastroparesis 5, 4.
• Consider upper endoscopy if alarm features develop (weight loss, dysphagia, persistent vomiting) 1, 8.

Common Pitfalls to Avoid

• Do not dismiss the 3-month gap in thyroid medication as inconsequential—this is the likely primary driver of her symptom complex 2, 3.
• Do not attribute all symptoms to gastroenteritis without addressing the underlying hypothyroidism 7, 8.
• Do not use antimotility agents (loperamide) for her constipation as these can worsen gastroparesis symptoms 4.
• Do not delay thyroid hormone replacement while pursuing extensive GI workup; start levothyroxine immediately based on clinical presentation 3.
• Do not overlook dehydration as a contributor to both her GI symptoms and near-syncope episode 1.