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3.4 Celiac Disease & Irritable Bowel Syndrome
ABIM Internal Medicine Exam
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1 Chapter 0: The ABIM Exam, Blueprint & Study Strategy
0.1 Exam Format, Question Types & the 2026 Blueprint 0.2 Eligibility, Registration, Fees & Exam-Day Logistics 0.3 Scoring, the Passing Standard & Score Reports 0.4 Building a Blueprint-Weighted Study Plan
2 Chapter 1: Cardiovascular Disease (14% of Exam)
1.1 Ischemic Heart Disease & Acute Coronary Syndromes 1.2 Antithrombotic Therapy, Secondary Prevention & Mechanical Complications of MI 1.3 Atrial Fibrillation, Atrial Flutter & Stroke Prevention 1.4 Supraventricular Tachycardias, Ventricular Arrhythmias & Bradycardias 1.5 Heart Failure: Classification, Staging & Guideline-Directed Medical Therapy 1.6 Device Therapy, HFpEF & the Cardiomyopathies 1.7 Valvular Heart Disease & Endocarditis Prophylaxis 1.8 Pericardial Disease & Acute Aortic Syndromes 1.9 Hypertension: Classification, Diagnosis & Secondary Causes 1.10 Hypertensive Crises & Dyslipidemia 1.11 Adult Congenital Heart Disease & Coarctation of the Aorta 1.12 Syncope: Reflex, Orthostatic & Cardiac Causes 1.13 Cardiac Physical Examination, Murmurs & Antithrombotic Selection
3 Chapter 2: Endocrinology, Diabetes & Metabolism (9% of Exam)
2.1 Diabetes Mellitus: Diagnosis, Glycemic Targets & Pharmacotherapy 2.2 Insulin Therapy, Hyperglycemic Emergencies & Chronic Complications 2.3 Thyroid Function Testing & Hypothyroidism 2.4 Thyrotoxicosis, Thyroid Storm & Thyroid Nodules 2.5 Adrenal & Pituitary Disorders 2.6 Hypercalcemia, Hypocalcemia & Disorders of Mineral Metabolism 2.7 Osteoporosis & Paget Disease of Bone 2.8 Ovarian, Testicular & Reproductive Endocrine Disorders 2.9 Hypoglycemia, Endocrine Tumors, Polyglandular Syndromes & Severe Hypertriglyceridemia
4 Chapter 3: Gastroenterology & Hepatology (9% of Exam)
3.1 Esophageal Disease 3.2 Stomach & Duodenal Disease and Gastrointestinal Hemorrhage 3.3 Inflammatory Bowel Disease 3.4 Celiac Disease & Irritable Bowel Syndrome 3.5 Diverticular Disease & Colorectal Cancer Screening 3.6 Viral Hepatitis, Steatotic & Alcohol-Associated Liver Disease 3.7 Cirrhosis & the Complications of Portal Hypertension 3.8 Acute Pancreatitis 3.9 Chronic Pancreatitis & Biliary Tract Disease 3.10 Inherited, Autoimmune & Drug-Induced Liver Disease 3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV
5 Chapter 4: Infectious Disease (9% of Exam)
4.1 Lower Respiratory Tract Infections & Sepsis Syndromes 4.2 Viral Respiratory Pathogens & Tuberculosis 4.3 Central Nervous System Infections 4.4 Skin, Soft Tissue, Bone & Joint Infections 4.5 Infective Endocarditis & Cardiovascular Infection 4.6 Clostridioides difficile & Catheter-Related Bloodstream Infection 4.7 HIV Diagnosis, Antiretroviral Therapy & Prevention 4.8 Opportunistic Infections & Sexually Transmitted Infections 4.9 Fever of Unknown Origin, Neutropenic Fever & Toxic Shock 4.10 Travel-Related Illness, Vector-Borne Disease & Outbreaks 4.11 Infection Prevention, Nosocomial Infection & Postexposure Prophylaxis 4.12 Rheumatic Fever, Poststreptococcal Disease, Enteric & Hepatic Infections
6 Chapter 5: Pulmonary Disease (9% of Exam)
5.1 COPD: Diagnosis, GOLD Classification & Initial Pharmacotherapy 5.2 Interventions That Reduce COPD Mortality & Exacerbation Management 5.3 Asthma: Diagnosis, Stepwise Therapy & Status Asthmaticus 5.4 Interstitial Lung Disease & Idiopathic Pulmonary Fibrosis 5.5 Sarcoidosis, Hypersensitivity Pneumonitis & Occupational Lung Disease 5.6 Pulmonary Embolism: Diagnosis, Risk Stratification & Anticoagulation 5.7 Pulmonary Hypertension & Sleep-Disordered Breathing 5.8 Acute Respiratory Distress Syndrome & Mechanical Ventilation 5.9 Pleural Disease, Empyema & Pneumothorax 5.10 Bronchiectasis, Cystic Fibrosis & Restrictive Lung Disease 5.11 Evaluation of Cough, Dyspnea, Hemoptysis & the Solitary Pulmonary Nodule
7 Chapter 6: Rheumatology & Orthopedics (9% of Exam)
6.1 Rheumatoid Arthritis: Diagnosis & Systemic Manifestations 6.2 Antirheumatic Pharmacotherapy & the Spondyloarthropathies 6.3 Gout: Pathophysiology & Acute Management 6.4 Urate-Lowering Therapy & Calcium Pyrophosphate Deposition Disease 6.5 Osteoarthritis 6.6 Systemic Lupus Erythematosus 6.7 Systemic Sclerosis, Sjogren Syndrome & Inflammatory Myopathies 6.8 The Vasculitides 6.9 Regional Musculoskeletal Syndromes, Back Pain & Sports Injuries 6.10 Other Primary Rheumatic Disorders & Mixed Connective Tissue Disease 6.11 Osteonecrosis & Metabolic Bone Disease
8 Chapter 7: Hematology (6% of Exam)
7.1 Approach to Anemia & the Microcytic Anemias 7.2 Macrocytic, Normocytic & Hemolytic Anemias 7.3 Hemoglobinopathies, Thalassemias & Paroxysmal Nocturnal Hemoglobinuria 7.4 Platelet Disorders, Thrombocytopenia & the Bleeding Patient 7.5 Coagulation Factor Disorders, Thrombophilia & Anticoagulant Reversal 7.6 Acute Leukemias, Chronic Leukemias & Myeloproliferative Neoplasms 7.7 Lymphomas & Plasma Cell Disorders 7.8 Myelodysplastic Syndrome, Myeloproliferative Neoplasms & Porphyria 7.9 Transfusion Medicine & Late Complications of Transplantation
9 Chapter 8: Medical Oncology (6% of Exam)
8.1 Breast, Lung, Colorectal & Prostate Cancer 8.2 Oncologic Emergencies 8.3 Genitourinary & Gynecologic Malignancies 8.4 Head and Neck, Bone & Soft Tissue Cancer and Cancer of Unknown Primary 8.5 Complications of Cancer & Its Treatment 8.6 Cancer Prevention, Survivorship & Psychosocial Care
10 Chapter 9: Nephrology & Urology (6% of Exam)
9.1 Acute Kidney Injury: Staging, Etiology & Urine Microscopy 9.2 Glomerular Disorders & Nephrotic Syndrome 9.3 Nephritic Syndromes, RPGN & Indications for Renal Replacement Therapy 9.4 Chronic Kidney Disease: Staging & Progression Retardation 9.5 Complications of Chronic Kidney Disease: Anemia, CKD-MBD & Acidosis 9.6 Hyponatremia, Hypernatremia & Water Balance 9.7 Potassium Disorders & Systematic Acid-Base Analysis 9.8 Renal Tubular Acidosis & Nephrolithiasis 9.9 Prostate Disorders, Urinary Incontinence & Other Urologic Conditions 9.10 Cystic Kidney Disease, Obstructive Uropathy, Tubulointerstitial Disease & Hematuria
11 Chapter 10: Neurology (4% of Exam)
10.1 Acute Ischemic Stroke: Syndromes & Reperfusion 10.2 Transient Ischemic Attack, Secondary Prevention & Hemorrhagic Stroke 10.3 Headache & Facial Pain 10.4 Seizures, Epilepsy & Movement Disorders 10.5 Multiple Sclerosis & Neuromuscular Junction Disorders 10.6 Motor Neuron Disease & Acute Peripheral Neuropathy 10.7 Cranial Neuropathies & Neuro-Ophthalmology 10.8 Peripheral Neuropathies, CNS Tumors & Other Neurologic Disorders
12 Chapter 11: Psychiatry & Behavioral Health (4% of Exam)
11.1 Major Depressive Disorder & Medical Mimics 11.2 Antidepressant Pharmacotherapy & Treatment-Resistant Depression 11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity 11.4 Anxiety, Stress-Related & Obsessive-Compulsive Disorders 11.5 Alcohol Use Disorder & Withdrawal 11.6 Pharmacotherapy for Alcohol & Opioid Use Disorder 11.7 Toxidromes, Psychiatric Emergencies & Suicide Risk Assessment 11.8 Psychotic, Somatic Symptom, Factitious & Personality Disorders 11.9 Eating Disorders, Sleep Disorders & Sexual Health
13 Chapter 12: Dermatology (3% of Exam)
12.1 Dermatitis, Papulosquamous & Inflammatory Dermatoses 12.2 Acne, Rosacea & Cutaneous Infections 12.3 Herpes Zoster & Autoimmune Blistering Diseases 12.4 Nodules, Tumors & Cutaneous Oncology 12.5 Dermatologic Emergencies & Severe Cutaneous Adverse Reactions 12.6 Pigment Disorders, Alopecia, Nail Disease & Photosensitivity 12.7 Vascular Dermatoses, Environmental Injury & Cutaneous Signs of Systemic Disease
14 Chapter 13: Obstetrics & Gynecology / Women's Health (3% of Exam)
13.1 Contraception, Preconception Care & Teratogenicity 13.2 Hypertensive Disorders of Pregnancy & Gestational Diabetes 13.3 Thyroid Disease & Venous Thromboembolism in Pregnancy 13.4 Menopause & Menopausal Hormone Therapy 13.5 Abnormal Uterine Bleeding, Endometrial Disease & Gynecologic Cancer Screening 13.6 Breast Disorders & Diseases of the Vulva and Vagina 13.7 Menstrual Disorders, Fibroids, Endometriosis & Early Pregnancy Complications
15 Chapter 14: Geriatric Syndromes (3% of Exam)
14.1 Comprehensive Geriatric Assessment & Frailty 14.2 Falls, Gait Assessment & Polypharmacy 14.3 Urinary Incontinence & Pressure Injuries in Older Adults 14.4 Mild Cognitive Impairment, Dementia & Its Subtypes 14.5 Delirium & the Pharmacotherapy of Cognitive Disorders 14.6 Palliative Care, Hospice & Advance Care Planning 14.7 Chronic Wounds, Nutrition, Swallowing, Constipation & Hip Fracture 14.8 Sensory Impairment, Dizziness, Elder Mistreatment & Care Settings
16 Chapter 15: Allergy & Immunology (2% of Exam)
15.1 Anaphylaxis: Recognition & Emergency Management 15.2 Urticaria & Angioedema 15.3 Drug Allergy, Desensitization & Adult Immunodeficiency 15.4 Food Allergy, Insect Venom Hypersensitivity, Serum Sickness & Contrast Reactions 15.5 Rhinitis, Conjunctivitis, Eosinophilic & Mast Cell Disorders
17 Chapter 16: Preventive Medicine, Immunization & Clinical Epidemiology
16.1 The USPSTF Framework & Evidence-Based Cancer Screening 16.2 Cardiovascular & Metabolic Screening and Primary Prevention 16.3 Adult Immunization & Vaccines in Special Populations 16.4 Clinical Epidemiology, Biostatistics & Study Design
18 Chapter 17: Miscellaneous - Ethics, Patient Safety & Quality Improvement (2% of Exam)
17.1 Principles of Bioethics & Decisional Capacity 17.2 Informed Consent, Treatment Refusal & Special Scenarios 17.3 Surrogate Decision-Making, Advance Directives & Confidentiality 17.4 Patient Safety Science, Medical Error & Diagnostic Reasoning 17.5 Quality Improvement Methods, Health Disparities & Health Equity
19 Chapter 18: Perioperative Medicine & Medical Consultation
18.1 Preoperative Cardiovascular Risk Assessment 18.2 Preoperative Pulmonary Risk & Perioperative Medication Management 18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications
20 Chapter 19: Ophthalmology (1% of Exam)
19.1 The Acute Red Eye & Ophthalmic Emergencies 19.2 Painless Vision Loss & Chronic Ophthalmic Disease 19.3 Uveitis, Scleritis & Orbital Disease
21 Chapter 20: Otolaryngology & Dental Medicine (1% of Exam)
20.1 Dizziness, Vertigo & Epistaxis 20.2 Ear Disorders, Hearing Loss & Upper Respiratory Infections 20.3 Oral Cavity, Salivary Gland, Laryngeal & Taste and Smell Disorders
3.4 Celiac Disease & Irritable Bowel Syndrome
Key Takeaways Explain This Topic AI
Tissue transglutaminase IgA testing requires a simultaneous total IgA level, because selective IgA deficiency is over-represented in celiac disease and produces false-negative results.
Serology and biopsy are only interpretable while the patient is consuming gluten; a gluten-free diet before testing invalidates both.
Dermatitis herpetiformis is the cutaneous manifestation of celiac disease and is itself sufficient to establish the diagnosis in the right serologic context.
Irritable bowel syndrome is diagnosed from recurrent abdominal pain related to defecation or a change in stool form or frequency, in the absence of alarm features.
Alarm features including onset after age 50, weight loss, nocturnal symptoms, bleeding, anemia or a family history of colorectal cancer or inflammatory bowel disease mandate further evaluation.
Last updated: August 2026
- 1. Celiac Disease (Gluten-Sensitive Enteropathy)
- Pathophysiology & Genetics
Autoimmune enteropathy triggered by ingestion of dietary gluten (specifically the gliadin peptide fraction found in wheat, rye, and barley ).
Strongly associated with Human Leukocyte Antigens HLA-DQ2 (95%) and HLA-DQ8 (5%) .
Clinical Manifestations
Gastrointestinal: Chronic osmotic/secretory diarrhea, steatorrhea (pale, bulky, foul-smelling stools), flatulence, abdominal bloating, and weight loss.
Extraintestinal / Malabsorptive: Refractory iron deficiency anemia, premature osteopenia/osteoporosis (calcium/vitamin D malabsorption), aphthous stomatitis, elevated transaminases, peripheral neuropathy, and ataxia.
Dermatitis Herpetiformis: Pathognomonic cutaneous manifestation characterized by intensely pruritic, grouped, polymorphic erythematous papules and vesicles distributed symmetrically over the extensor surfaces (elbows, knees, buttocks, scalp, upper back).
Diagnosis: Direct immunofluorescence (DIF) of perilesional skin punch biopsy demonstrates granular IgA deposition in the dermal papillae .
Treatment: Strict lifelong gluten-free diet and oral Dapsone (must check baseline G6PD level to prevent acute hemolytic anemia).
Diagnostic Evaluation
Warning
Patients MUST be on a gluten-containing diet (at least 1–2 slices of wheat bread daily for 6–8 weeks) at the time of serologic and histologic testing. Testing while on a gluten-free diet causes false-negative results.
Step 1 — Serologic Testing:
Order serum IgA Tissue Transglutaminase (tTG-IgA) antibody PLUS Total Serum IgA .
The Total IgA Pitfall: Patients with Celiac disease have a 10- to 15-fold higher prevalence of Selective IgA Deficiency . In patients with IgA deficiency ( total IgA < 20 mg/dL \text{total IgA} < 20\text{ mg/dL} total IgA < 20 mg/dL ), tTG-IgA will be falsely negative. In this setting, order IgG-based testing : Deamidated Gliadin Peptide IgG (DGP-IgG) or tTG-IgG .
Step 2 — Confirmatory Endoscopy & Histopathology:
EGD with multiple duodenal mucosal biopsies (1–2 biopsies from the duodenal bulb and ≥ 4 \ge 4 ≥ 4 biopsies from the second/third portion of the duodenum).
Marsh Classification Hallmark Findings:
Intraepithelial lymphocytosis ( > 25 >25 > 25 intraepithelial lymphocytes per 100 enterocytes).
Crypt hyperplasia.
Blunting and total atrophy of intestinal villi (villous flattening).
Long-Term Management & Complications:
Strict lifelong Gluten-Free Diet (eliminate wheat, barley, rye; pure uncontaminated oats are generally safe in moderation).
Monitor adherence by checking tTG-IgA serology at 6 and 12 months post-dietary initiation.
Perform baseline DEXA scan for metabolic bone disease; replenish iron, folate, B12, vitamin D, and zinc.
Malignancy Risk: Increased risk of Enteropathy-Associated T-Cell Lymphoma (EATL) and small bowel adenocarcinoma in patients with refractory or poorly controlled disease.
2. Irritable Bowel Syndrome (IBS)
Irritable Bowel Syndrome (IBS) is a disorder of gut-brain interaction characterized by recurrent abdominal pain associated with altered bowel habits.
Rome IV Diagnostic Criteria
Recurrent abdominal pain on average at least 1 day per week in the last 3 months , with symptom onset at least 6 months prior, associated with ≥ 2 \ge 2 ≥ 2 of the following features :
Related to defecation (either improved or worsened by defecation).
Associated with a change in the frequency of stool .
Associated with a change in the form (appearance) of stool (according to the Bristol Stool Form Scale).
IBS Subtypes (Bristol Stool Scale)
IBS-D (Diarrhea-predominant): > 25 % >25\% > 25% stools Bristol types 6–7 (loose/watery) and < 25 % <25\% < 25% Bristol types 1–2 (hard/lumpy).
IBS-C (Constipation-predominant): > 25 % >25\% > 25% stools Bristol types 1–2 and < 25 % <25\% < 25% Bristol types 6–7.
IBS-M (Mixed): > 25 % >25\% > 25% stools Bristol types 1–2 AND > 25 % >25\% > 25% Bristol types 6–7.
Red Flag Alarm Features (Requiring Organic Workup / Colonoscopy)
Age ≥ 50 \ge 50 ≥ 50 years at symptom onset without prior CRC screening.
Unexplained unintentional weight loss.
Nocturnal diarrhea waking the patient from sleep.
Overt rectal bleeding or melena.
Unexplained iron deficiency anemia.
Family history of colorectal cancer, IBD, or celiac disease.
Palpable abdominal mass or lymphadenopathy.
Evidence-Based Pharmacotherapy
IBS Subtype First-Line & Dietary Interventions Targeted Pharmacotherapy Options
All Subtypes • Low-FODMAP diet (Fermentable Oligo-, Di-, Monosaccharides, and Polyols); • Soluble Fiber (Psyllium / Ispaghula husk 20–30 g/day; avoid insoluble bran which worsens gas/bloating) • Tricyclic Antidepressants (TCAs): Amitriptyline, Desipramine (10–50 mg qhs for visceral pain neuromodulation via anticholinergic and central analgesic effects).
IBS-D • Dietary avoidance of lactose, caffeine, artificial sweeteners • Loperamide (2–4 mg prn 30 min before meals); • Antispasmodics: Dicyclomine (10–20 mg QID), Hyoscyamine; • Rifaximin: 550 mg TID for 14 days (non-absorbable antibiotic, can be repeated up to 2 times for recurrent symptoms); • Eluxadoline: Mixed μ \mu μ -opioid receptor agonist (100 mg BID; contraindicated in patients without a gallbladder, history of pancreatitis, or alcohol excess due to risk of sphincter of Oddi spasm ).
IBS-C • Increased fluid intake, regular aerobic exercise • Osmotic Laxative: Polyethylene Glycol (PEG 3350, 17 g daily); • Secretagogues: ; - Lubiprostone: Chloride channel (ClC-2) activator (8 mcg BID for women); - Linaclotide: Guanylate cyclase-C agonist (72–290 mcg daily); - Plecanatide: Guanylate cyclase-C agonist (3 mg daily); • Prokinetic: Prucalopride (selective 5-HT4 receptor agonist, 1–2 mg daily).