What is the most likely diagnosis and appropriate management for a patient with marked eosinophilia, iron-deficiency anemia, left upper quadrant abdominal pain, fatigue, nausea, and early satiety?

Eosinophilic Gastroenteritis with Parasitic Infection as Primary Differential

The most likely diagnosis is eosinophilic gastroenteritis (EGE), but parasitic helminth infection—particularly schistosomiasis or strongyloidiasis—must be excluded first given the marked eosinophilia, and this exclusion takes diagnostic priority before initiating immunosuppressive therapy. 1

Immediate Diagnostic Priorities

Rule Out Parasitic Infection First

• Obtain concentrated stool microscopy (three samples) and Strongyloides serology immediately before any treatment, as these have high diagnostic yield and helminth infection is frequently asymptomatic despite marked eosinophilia 1
• Schistosomiasis can present with LUQ pain, marked eosinophilia (often >5 × 10⁹/L), nausea, and abdominal symptoms 2-8 weeks after freshwater exposure; schistosomiasis serology should be sent 1
• Toxocara serology should be obtained, as visceral larva migrans causes abdominal pain, hepatosplenomegaly, and marked eosinophilia 1
• If any travel history to endemic regions exists, empirical treatment with albendazole 400 mg plus ivermectin 200 μg/kg should be considered while awaiting results, but exclude Loa loa exposure before giving ivermectin 1

Confirm Iron Deficiency Anemia

• Verify iron deficiency with serum ferritin <30 mcg/L (or <100 mcg/L if inflammation present) and transferrin saturation <16% 2, 3
• Ferritin may be falsely elevated as an acute phase reactant in the setting of eosinophilic inflammation 2, 4

Secondary Diagnostic Evaluation: Eosinophilic Gastroenteritis

When to Suspect EGE

Once parasitic causes are excluded, EGE becomes the leading diagnosis when:

• Marked peripheral eosinophilia (85.7% of EGE cases) is present 5
• LUQ pain, early satiety, nausea, and fatigue are the dominant symptoms 6, 7
• History of atopy, asthma, eczema, or allergic rhinitis exists (present in 25-75% of EGE cases) 8, 7
• Elevated serum IgE (71.4% of EGE cases) 5

Endoscopic Evaluation

Upper endoscopy with multiple biopsies from stomach and duodenum is mandatory to demonstrate eosinophilic infiltration (>20-30 eosinophils per high-power field in gastric or intestinal mucosa) 8, 6

Expected endoscopic findings in EGE include:

• Small patchy mucosal erythema or erosions (75% of cases) 5
• Mucosal fold thickening (17.9%) 5
• Submucosal nodules (21.4%) 5
• Small gastroduodenal ulcers (14.3%) 5

During the same endoscopy, obtain duodenal biopsies to screen for celiac disease, which accounts for 3-5% of iron deficiency anemia cases and can coexist with eosinophilic disorders 2, 3, 4

Complete the Anemia Work-Up

Bidirectional endoscopy (colonoscopy in addition to upper endoscopy) is strongly recommended because:

• Dual pathology occurs in 10-15% of iron deficiency anemia cases 1, 2, 4
• Colorectal or gastric malignancy must be excluded in any adult with unexplained iron deficiency anemia 2, 3, 4
• EGE can involve the colon, and colonic biopsies may be diagnostic 6, 7

Treatment Algorithm

If Parasitic Infection is Confirmed

• Schistosomiasis: Praziquantel 40 mg/kg single dose, repeated at 6-8 weeks; consider prednisone 20 mg daily for 5 days if Katayama syndrome features are present 1
• Strongyloidiasis/hookworm/ascariasis: Albendazole 400 mg twice daily for 3 days 1
• Toxocariasis: Albendazole 400 mg twice daily for 5 days 1

If Eosinophilic Gastroenteritis is Confirmed

Initiate oral prednisone 20-40 mg daily for 2-4 weeks as first-line therapy, which achieves remission in most patients (75-100% response rate) 8, 9, 5

Alternative or adjunctive approaches:

• Food allergen testing with elimination diet (particularly dairy, wheat, eggs, soy) 6, 7
• Loratadine, proton pump inhibitors, and dietary modification achieved remission in 62.5% of patients in one series 5
• Leukotriene receptor antagonists or mast cell stabilizers as steroid-sparing agents 7

Relapse occurs in 25% of patients after steroid withdrawal, requiring either repeat courses or maintenance therapy 5

Concurrent Iron Replacement

Start oral ferrous sulfate 200 mg three times daily (65 mg elemental iron per dose) immediately, regardless of investigation results 2

• Continue for 3 months after hemoglobin normalizes to replenish stores 1, 2
• If oral iron is not tolerated or ineffective, intravenous iron should be administered 1

Critical Pitfalls to Avoid

• Never start corticosteroids before excluding Strongyloides infection, as immunosuppression can trigger hyperinfection syndrome with disseminated strongyloidiasis and high mortality 1
• Do not accept minor endoscopic findings (erosions, small ulcers) as the sole explanation for iron deficiency without completing colonoscopy 1, 4
• Do not stop investigation after finding one cause; multiple etiologies coexist in 10-15% of cases 2, 4
• Failure to screen for celiac disease results in missed diagnoses in 3-5% of iron deficiency anemia cases 2, 3, 4
• EGE has a 25% relapse rate, so arrange close follow-up and do not assume permanent remission after initial treatment response 5