What is the differential diagnosis for a patient with vomiting responsive only to intravenous (IV) medications, inability to keep food and oral medications down, and abdominal pain, particularly in the left lower quadrant?

Differential Diagnosis for Vomiting Responsive Only to IV Medications with Left Lower Quadrant Pain

The most likely diagnosis is acute left-sided colonic diverticulitis, which is the most common cause of left lower quadrant pain in adults and can present with severe vomiting requiring IV antiemetics when complicated by obstruction or severe inflammation. 1

Immediate Life-Threatening Considerations

Obtain CT abdomen/pelvis with IV contrast immediately to identify the source and guide treatment, as clinical diagnosis alone has poor accuracy (sensitivity 0.68, specificity 0.98) and imaging changes management in 25% of cases. 1

Critical diagnoses requiring urgent surgical consultation include:

• Perforated diverticulitis with peritonitis - presents with severe left lower quadrant pain, vomiting, fever, and signs of sepsis; mortality increases from 1.2% without sepsis to 67.8% with septic shock 1
• Bowel obstruction from sigmoid diverticulitis - causes progressive vomiting (initially gastric, then bilious), inability to pass flatus or stool, and abdominal distension 1, 2
• Colonic perforation from cancer or diverticulitis - presents with peritoneal signs, free air on CT, and hemodynamic instability 1
• Mesenteric ischemia - characterized by pain out of proportion to exam findings and carries 30-90% mortality 3

Primary Differential Diagnoses for Left Lower Quadrant Pain with Severe Vomiting

Acute Left-Sided Colonic Diverticulitis (Most Common)

• Accounts for the majority of left lower quadrant pain cases in Western populations, with prevalence rising 50% between 2000-2007 1
• Presents with acute left lower quadrant pain or tenderness, elevated inflammatory markers (CRP, WBC), and may cause vomiting when complicated by obstruction or severe inflammation 1
• Only 50% of elderly patients have typical left lower quadrant pain, with 17% having fever and 43% lacking leukocytosis, making clinical diagnosis unreliable 1
• CT findings include bowel wall thickening, pericolic fat stranding, and potential complications (abscess, perforation, obstruction) 1

Large Bowel Obstruction

• Presents with colic-like abdominal pain, abdominal bloating, absence of flatus/bowel movements, and progressive vomiting (initially gastric, then bilious) 1, 2
• Vomiting is less frequent than in small bowel obstruction but becomes prominent as obstruction progresses 1
• Physical exam shows abdominal distension (65.3%), absent bowel sounds, and tenderness without peritoneal signs unless perforation occurs 1
• Causes include colon cancer (especially in patients with bloody stools or rectal bleeding), diverticular stricture, or volvulus 1, 2

Complicated Diverticulitis with Abscess

• Presents with persistent left lower quadrant pain, fever, and severe vomiting requiring IV medications 1
• Abscesses >3-4 cm require percutaneous drainage plus IV antibiotics; smaller abscesses may respond to antibiotics alone 1
• CT demonstrates pericolic fluid collection, often with rim enhancement 1

Inflammatory Bowel Disease (Crohn's Disease or Ulcerative Colitis)

• Can present with left lower quadrant pain, bloody diarrhea, weight loss, and vomiting when complicated by stricture or severe inflammation 1
• More common in younger patients but can present at any age 1

Epiploic Appendagitis

• Causes acute focal left lower quadrant pain without systemic symptoms (no fever, normal WBC) 1
• Self-limited condition managed conservatively with NSAIDs 1
• CT shows oval fatty lesion adjacent to colon with surrounding inflammatory changes 1

Secondary Considerations

Gynecologic Pathology (in Women)

• Ovarian torsion, ruptured ovarian cyst, tubo-ovarian abscess, or ectopic pregnancy can cause left lower quadrant pain with vomiting 1
• Requires pelvic ultrasound and gynecology consultation 1

Urologic Causes

• Pyelonephritis - presents with fever, costovertebral angle tenderness, pyuria, and vomiting 1, 3
• Urolithiasis - causes colicky flank pain radiating to groin, hematuria, and vomiting from severe pain 1

Small Bowel Obstruction

• Presents with crampy periumbilical pain, early bilious vomiting, and inability to pass flatus 4
• Vomiting is more prominent and occurs earlier than in large bowel obstruction 4

Gastroparesis or Cyclic Vomiting Syndrome

• Causes severe nausea and vomiting responsive only to IV medications (particularly ondansetron) 5, 4
• Gastroparesis presents with early satiety, postprandial vomiting, and abdominal discomfort; treated with metoclopramide 4
• Cyclic vomiting syndrome causes episodic severe vomiting with symptom-free intervals; requires specialist follow-up 4

Diagnostic Algorithm

Step 1: Assess Hemodynamic Stability and Sepsis

• Check vital signs for hypotension (MAP <65 mmHg), tachycardia, fever, or altered mental status indicating sepsis or septic shock 1
• Obtain lactate level; lactate >2 mmol/L with vasopressor requirement defines septic shock with 67.8% mortality 1
• Examine for peritoneal signs (guarding, rebound tenderness, absent bowel sounds) indicating perforation requiring emergent surgery 1

Step 2: Obtain Laboratory Studies

• Complete blood count (leukocytosis suggests infection/inflammation) 1
• Comprehensive metabolic panel (electrolyte abnormalities from vomiting, elevated creatinine from dehydration) 1
• C-reactive protein (CRP >175 mg/L suggests complicated diverticulitis, though 39% of complicated cases have lower CRP) 1
• Lactate dehydrogenase (elevated in bowel ischemia or obstruction) 2
• Urinalysis (rule out urinary tract infection or nephrolithiasis) 1

Step 3: Obtain CT Abdomen/Pelvis with IV Contrast

• CT is the most useful examination for left lower quadrant pain with sensitivity and specificity near 100% for most causes 1
• IV contrast improves detection of bowel wall pathology, pericolic abnormalities, vascular pathology, and fluid collections 1
• Unenhanced CT has similar accuracy (64-68%) to contrast-enhanced CT (68-71%) in elderly patients when contrast is contraindicated 1
• CT identifies diverticulitis, abscess, perforation (free air), obstruction, cancer, and alternative diagnoses 1

Step 4: Initiate Supportive Care

• Place nasogastric tube for bowel decompression if obstruction suspected (reduces vomiting and abdominal distension) 2, 4
• IV fluid resuscitation with crystalloids to correct dehydration and electrolyte abnormalities 1, 4
• IV ondansetron 4 mg over 2-5 minutes for severe vomiting unresponsive to oral medications; repeat dosing does not provide additional benefit 5
• NPO (nothing by mouth) until diagnosis established 2, 4

Management Based on Diagnosis

Uncomplicated Diverticulitis (No Abscess, No Perforation, No Obstruction)

• Antibiotics can be avoided in immunocompetent patients without sepsis or significant comorbidities, as antibiotic treatment does not accelerate recovery or prevent complications 1
• If antibiotics used: Ertapenem 1g IV q24h or Eravacycline 1mg/kg IV q12h for community-acquired infection 3
• Bowel rest with clear liquids, advance diet as tolerated 1
• Close clinical monitoring to assess for resolution of inflammation 1

Complicated Diverticulitis with Abscess

• Abscesses <3-4 cm: IV antibiotics alone (Ertapenem 1g q24h or Eravacycline 1mg/kg q12h) 1, 3
• Abscesses ≥3-4 cm: Percutaneous drainage plus IV antibiotics 1
• If percutaneous drainage not feasible or patient has septic shock: Meropenem 1g IV q6h by extended infusion, Doripenem 500mg IV q8h by extended infusion, or Imipenem/cilastatin 500mg IV q6h by extended infusion 3
• Antibiotic duration: 4 days post-source control for uncomplicated infections; extend to 7 days for immunocompromised or critically ill patients 3

Perforated Diverticulitis or Bowel Obstruction

• Emergent surgical consultation for peritonitis, free air on CT, hemodynamic instability, or clinical deterioration despite medical management 1
• Broad-spectrum IV antibiotics immediately (Meropenem, Doripenem, or Imipenem/cilastatin as above) 3
• Aggressive fluid resuscitation and correction of electrolyte abnormalities 1

Bowel Obstruction from Cancer or Other Causes

• Nasogastric decompression, IV fluids, and correction of electrolyte disturbances 1, 4
• Surgical consultation to determine need for operative intervention versus conservative management 1
• If malignant obstruction: Consider octreotide and corticosteroids to reduce nausea/vomiting 6

Gastroparesis or Cyclic Vomiting

• Metoclopramide is the mainstay of therapy for gastroparesis 4
• For cyclic vomiting: IV ondansetron 4 mg, volume and electrolyte repletion, and gastroenterology follow-up 4

Critical Pitfalls to Avoid

• Do not rely on clinical assessment alone, as misdiagnosis rates are 34-68% without imaging and clinical diagnosis of diverticulitis has only 65% positive predictive value 1, 3
• Do not delay CT imaging in patients with severe vomiting requiring IV medications and left lower quadrant pain, as this combination suggests serious pathology requiring urgent diagnosis 1
• Do not assume normal WBC or absence of fever excludes serious pathology, as 43% of elderly patients with diverticulitis lack leukocytosis and only 17% have fever 1
• Do not discharge patients without definitive imaging when vomiting is severe enough to require IV medications, as this indicates either severe underlying disease or complications 1, 4
• Do not miss septic shock, defined by vasopressor requirement to maintain MAP ≥65 mmHg and lactate >2 mmol/L, which carries 67.8% mortality 1