What conditions are associated with elevated beta defensin 2, MMP (Matrix Metalloproteinase) 9, fecal lactoferrin, and fecal eosinophil protein X, with normal lysozyme, S100A12, and calprotectin, in a patient with chronic diarrhea and worsening gastrointestinal symptoms?

Differential Diagnosis: Eosinophilic Gastrointestinal Disease with Possible Bile Acid Diarrhea

The constellation of elevated fecal eosinophil protein X, elevated beta-defensin 2, elevated MMP-9, and elevated fecal lactoferrin with normal calprotectin and S100A12 most strongly suggests eosinophilic gastroenteritis or food protein-induced enteropathy, with bile acid diarrhea as a secondary consideration given the chronic nature and recent worsening with nocturnal symptoms.

Primary Diagnostic Consideration: Eosinophilic Gastrointestinal Disease

Key Distinguishing Features

• Elevated fecal eosinophil protein X is the critical finding that points toward eosinophilic infiltration of the gastrointestinal tract, which can occur without significant neutrophilic inflammation (hence normal calprotectin and S100A12) 1.

• The presence of mucus in stool, intermittent rash, bloating, and gas are consistent with food protein sensitivity or eosinophilic gastroenteritis, which can present with these exact symptoms 2.

• **Normal calprotectin (<50 mg/kg) and normal S100A12 effectively exclude active inflammatory bowel disease** (IBD), as both markers have >90% sensitivity for IBD and would be markedly elevated if Crohn's disease or ulcerative colitis were present 2, 1.

Understanding the Biomarker Pattern

• Elevated beta-defensin 2 (HBD-2) indicates activation of the innate immune system but is NOT specific for IBD—it can be elevated in irritable bowel syndrome and other functional disorders with low-grade mucosal immune activation 3.

• Elevated MMP-9 reflects tissue remodeling and can occur in eosinophilic conditions, food sensitivities, and microscopic inflammation without frank IBD 3.

• Elevated fecal lactoferrin with normal calprotectin is unusual but can occur when there is mucosal inflammation without significant neutrophil infiltration, as seen in eosinophilic disorders 2.

Secondary Consideration: Bile Acid Diarrhea

Clinical Features Supporting This Diagnosis

• Nocturnal diarrhea is an alarm feature that suggests organic disease and can occur with bile acid malabsorption, particularly when symptoms worsen over time 2, 4.

• Bile acid diarrhea typically presents with watery diarrhea that worsens after meals and can be associated with bloating and gas 2.

• The 3-year duration with recent worsening suggests a progressive process that could include bile acid malabsorption, especially if there is any history of cholecystectomy, ileal disease, or idiopathic bile acid malabsorption 2.

Recommended Testing

• The AGA suggests testing for bile acid diarrhea using SeHCAT scanning (not available in North America) or serum 7α-hydroxy-4-cholesten-3-one 2.

• If objective testing is unavailable, an empiric trial of bile acid binders (cholestyramine 4g before meals) is reasonable, with clinical response suggesting bile acid diarrhea as the cause 2.

Other Conditions to Exclude

Celiac Disease

• IgA tissue transglutaminase (tTG) with total IgA must be checked to exclude celiac disease, which can present with chronic diarrhea, bloating, and malabsorption 2, 5.

• For IgA-deficient patients, IgG-tTG or IgG deaminated gliadin peptides should be used 5.

Giardiasis

• Giardia antigen testing or PCR is strongly recommended due to high prevalence and excellent test performance in chronic diarrhea 2, 5.

• Giardiasis can cause chronic diarrhea with bloating, gas, and malabsorption without elevating calprotectin 6.

Microscopic Colitis

• Colonoscopy with biopsies from right and left colon is mandatory to exclude microscopic colitis, which has entirely normal-appearing mucosa on endoscopy but shows characteristic histologic changes 2, 4.

• Microscopic colitis cannot be diagnosed without histology and is a common cause of chronic secretory diarrhea, particularly in older adults 2, 6.

Mandatory Next Steps

Immediate Investigations Required

• Complete blood count, comprehensive metabolic panel, liver function tests, iron studies, vitamin B12, folate, and thyroid function tests to assess for anemia, malabsorption, and metabolic abnormalities 5, 4, 7.

• IgA-tTG with total IgA to screen for celiac disease 2, 5.

• Giardia antigen or PCR testing 2, 5.

• Colonoscopy with biopsies from right and left colon (not rectum) even if mucosa appears normal, to exclude microscopic colitis and assess for eosinophilic infiltration 2, 4.

Additional Testing Based on Initial Results

• Upper endoscopy with duodenal and gastric biopsies if eosinophilic gastroenteritis is suspected, to assess for eosinophilic infiltration throughout the GI tract 2.

• Allergy testing and empiric elimination diet (dairy, wheat, soy, eggs, nuts) if eosinophilic disease is confirmed, as food protein sensitivity is a common trigger 2.

• Bile acid testing or empiric trial of cholestyramine if other causes are excluded 2.

Critical Pitfalls to Avoid

• Do not assume IBS based on Rome IV criteria alone, as these have only 52-74% specificity and cannot exclude microscopic colitis, eosinophilic disease, or bile acid diarrhea 2, 4.

• Do not rely on calprotectin alone to exclude all organic disease—eosinophilic conditions and bile acid diarrhea can have normal calprotectin 2.

• Do not skip colonoscopy with biopsies, as microscopic colitis and eosinophilic colitis require histologic diagnosis and cannot be detected by imaging or stool markers alone 2, 4.

• Do not forget to check total IgA when testing for celiac disease, as IgA deficiency leads to false-negative tTG results 5, 8.