What is the most likely diagnosis and management for a 4-year-old girl with abdominal pain, vomiting, and fever for several days, with a normal ultrasound (USG) of the abdomen?

Acute Gastroenteritis with Consideration for Alternative Diagnoses

Most Likely Diagnosis

This 4-year-old girl most likely has acute viral gastroenteritis, but the normal ultrasound and 3-day symptom duration with recent fever onset warrant careful exclusion of non-gastrointestinal causes, particularly urinary tract infection, otitis media, pneumonia, or early appendicitis. 1

Critical Differential Considerations

The presentation of fever, vomiting, and abdominal pain with normal ultrasound requires systematic evaluation beyond simple gastroenteritis:

• Non-gastrointestinal infections including meningitis, bacterial sepsis, pneumonia, otitis media, and urinary tract infection commonly present with fever, vomiting, and abdominal pain in young children 1
• Early appendicitis may not show ultrasound findings initially, as ultrasound has limitations with sensitivity ranging 66-97% in pediatric patients and can miss early or retrocecal appendicitis 1
• Mesenteric lymphadenitis accounts for 12.7% of acute abdominal pain cases in hospitalized children 2

Immediate Diagnostic Workup Required

Essential Studies to Order Now:

• Urinalysis with microscopy and urine culture to exclude urinary tract infection/pyelonephritis, given the combination of abdominal pain and fever 3
• Complete blood count with differential to assess for leukocytosis suggesting bacterial infection or appendicitis 1
• Stool examination with methylene blue stain to identify white blood cells suggesting invasive bacterial enteritis requiring antimicrobial therapy 1
• Physical examination focus: Check for otitis media, assess lung sounds for pneumonia, evaluate for meningeal signs, and perform serial abdominal examinations for evolving peritoneal signs 1

When to Pursue Advanced Imaging:

• CT abdomen/pelvis should be considered if clinical suspicion for appendicitis remains high despite negative ultrasound, as CT demonstrates 90-100% sensitivity and 87-100% specificity in pediatric appendicitis 1
• CT is superior to ultrasound for excluding appendicitis, with negative likelihood ratios of 0-0.09 across studies 1

Hydration Assessment and Management

Evaluate Dehydration Severity:

Assess for clinical signs to categorize as mild (3-5%), moderate (6-9%), or severe (≥10%) dehydration 3, 4:

• Mild dehydration: Normal mental status, moist mucous membranes, normal skin turgor
• Moderate dehydration: Dry mucous membranes, decreased skin turgor, reduced urine output 3
• Severe dehydration: Altered mental status, prolonged capillary refill (>2 seconds), cool extremities, rapid deep breathing 3

Rehydration Protocol:

• For mild-moderate dehydration: Administer low-osmolarity oral rehydration solution (ORS) at 50-100 mL/kg over 3-4 hours 3, 4
• Replace ongoing losses: Give 10 mL/kg ORS for each watery stool and 2 mL/kg for each vomiting episode 3
• Ondansetron may be administered to children >4 years with significant vomiting to facilitate oral rehydration tolerance 3, 4
• Intravenous rehydration with isotonic fluids (lactated Ringer's or normal saline) at 20 mL/kg over 30 minutes is indicated for severe dehydration, shock, altered mental status, or failure of oral rehydration 3, 4

Nutritional Management

• Continue breastfeeding if applicable throughout the illness 3, 4
• Resume age-appropriate diet immediately after rehydration without fasting or dietary restriction 3, 4
• Avoid foods high in simple sugars (soft drinks, undiluted apple juice) as they exacerbate diarrhea through osmotic effects 1

Medications to Absolutely Avoid

• Loperamide is contraindicated in all children <18 years with acute diarrhea due to risk of severe abdominal distention, ileus, and death 1, 3, 4
• Antimotility agents, adsorbents, and antisecretory drugs do not reduce diarrhea volume or duration and can cause serious side effects 1, 3
• Do not use sports drinks or apple juice as primary rehydration fluids due to inappropriate osmolarity 3

Antimicrobial Therapy Considerations

Antimicrobial agents have limited usefulness since viral agents cause most acute gastroenteritis 1:

• Consider antibiotics only if: Bloody diarrhea with white blood cells on stool stain, recent antibiotic use (suspect Clostridium difficile), day care exposure with Shigella or Giardia prevalence, recent foreign travel, or immunodeficiency 1
• Watery diarrhea with vomiting in a child <2 years most likely represents viral gastroenteritis and does not require antimicrobial therapy 1

Admission Criteria

Hospitalize if any of the following are present 3:

• Severe dehydration (≥10% fluid deficit)
• Signs of shock or altered mental status
• Failure of oral rehydration therapy after 2-4 hours
• Intractable vomiting despite ondansetron
• Persistent tachycardia despite adequate rehydration suggesting underlying pathology

Critical Pitfalls to Avoid

• Do not assume viral gastroenteritis without excluding serious non-gastrointestinal infections that present identically in young children 1
• Do not rely solely on negative ultrasound to exclude appendicitis if clinical suspicion remains high, as ultrasound sensitivity is imperfect and appendix may not be visualized 1
• Do not delay rehydration while awaiting diagnostic test results; initiate ORS immediately 3
• Reassess after 2-4 hours of rehydration; if still dehydrated, reestimate deficit and restart rehydration or escalate to intravenous therapy 3