What are the differential diagnoses for a 19-year-old female presenting with smell sensitivity and vomiting for 2 weeks?

Differential Diagnoses for 19-Year-Old Female with Smell Sensitivity and Vomiting for 2 Weeks

The most critical diagnosis to rule out immediately in a 19-year-old female with smell sensitivity and vomiting for 2 weeks is pregnancy, followed by post-viral olfactory dysfunction (including COVID-19), and nausea and vomiting of pregnancy if pregnancy is confirmed. 1

Immediate Priority: Pregnancy Testing

• Pregnancy must be excluded first in any woman of childbearing age presenting with nausea, vomiting, and smell sensitivity, as it is the most common endocrinologic cause of these symptoms 1, 2
• Nausea and vomiting of pregnancy typically begins at 4-6 weeks gestation, peaks at 8-12 weeks, and is commonly associated with heightened smell sensitivity due to elevated human chorionic gonadotropin and estrogen levels 1
• The combination of smell sensitivity (hyperosmia) and vomiting lasting 2 weeks in a young female strongly suggests early pregnancy 1

If Pregnancy Test is Positive

• Diagnose as nausea and vomiting of pregnancy (NVP) and assess severity using the Motherisk Pregnancy-Unique Quantification of Emesis (PUQE) score to determine if this has progressed to hyperemesis gravidarum 1
• Early treatment is critical to prevent progression to hyperemesis gravidarum 1
• Initial management includes vitamin B6 (pyridoxine 10-25 mg every 8 hours) combined with doxylamine, which is FDA-approved for this indication 1

If Pregnancy Test is Negative: Post-Viral Olfactory Dysfunction

• The second most likely diagnosis is post-viral olfactory dysfunction with associated nausea, particularly COVID-19 or other viral upper respiratory infections 1
• Anosmia (complete smell loss) or altered smell perception (parosmia) occurs in 59-86% of COVID-19 patients and can present as the initial or isolated symptom 1
• Critically, parosmia (distorted smell perception) can cause profound nausea and vomiting when common food odors become disgusting, leading to loss of appetite and physical symptoms including vomiting 3
• Post-viral smell dysfunction typically develops 1-4 days after infection onset, with 73% of patients experiencing recovery within 7-14 days, though 20% have symptoms persisting beyond 14 days 1

Additional Differential Diagnoses to Consider

Gastrointestinal Causes

• Viral gastroenteritis: Usually self-limited with sudden onset, mild fever, and diarrhea, but 2-week duration makes this less likely 1, 4
• Functional gastrointestinal disorders: Including gastroparesis or cyclic vomiting syndrome, though these typically present with longer symptom duration 2, 5
• Food intolerance or formula intolerance: Can cause persistent vomiting but less likely to cause smell sensitivity 1

Neurologic Causes

• Migraine-associated nausea and vomiting: Migraines commonly cause osmophobia (smell sensitivity) and vomiting, and can present with prolonged symptoms 4, 2
• Increased intracranial pressure: From tumor, trauma, or other causes, though this would typically present with headache, neurologic signs, or altered mental status 1, 2

Metabolic and Endocrine Causes

• Metabolic disorders: Including diabetic ketoacidosis, thyroid disorders, or adrenal insufficiency, though these would typically have additional systemic symptoms 1, 2

Medication or Toxin-Related

• Medication adverse effects: Recent initiation of certain medications can cause both nausea and taste/smell alterations 4, 2
• Toxin exposure: Should be considered based on occupational or environmental history 2

Psychiatric Causes

• Eating disorders or psychiatric conditions: Can present with chronic nausea and vomiting, particularly in young females, though smell sensitivity is less typical 2, 5

Diagnostic Approach

Step 1: Obtain urine pregnancy test immediately 1, 2, 5

Step 2: Detailed history focusing on:

• Temporal relationship to any viral illness (fever, cough, myalgia, fatigue) 1
• Character of smell sensitivity: Is it heightened sensitivity (hyperosmia) or distorted smell (parosmia)? 3, 6
• Presence of nasal congestion or rhinorrhea (often absent in COVID-19 olfactory dysfunction) 1
• Headache patterns suggesting migraine 4
• Medication history and recent changes 4, 2
• Weight loss, dehydration, or inability to maintain oral intake 1, 5

Step 3: Physical examination:

• Vital signs and hydration status 5
• Nasal examination for rhinosinusitis or polyps 6
• Neurologic examination focusing on cranial nerves I, VII, IX, and X 6
• Abdominal examination to exclude acute abdomen 5

Step 4: Initial laboratory testing if indicated:

• Complete blood count, comprehensive metabolic panel to assess for dehydration, electrolyte abnormalities, or metabolic causes 5
• Thyroid-stimulating hormone if thyroid disorder suspected 5
• COVID-19 testing if post-viral etiology suspected 1

Common Pitfalls to Avoid

• Failing to test for pregnancy first in any woman of childbearing age with nausea and vomiting 1, 2
• Dismissing smell sensitivity as unimportant: This symptom strongly suggests either pregnancy or post-viral olfactory dysfunction and should guide the differential 1, 3
• Overlooking parosmia as a cause of nausea: Distorted smell perception can cause profound nausea and vomiting that persists as long as the smell disorder continues 3
• Ordering extensive imaging without clear indication: Most cases can be diagnosed with history, physical examination, and basic laboratory testing 2, 5
• Not recognizing that COVID-19 can present with isolated olfactory symptoms: Anosmia can be the only presenting symptom without typical respiratory manifestations 1