3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV

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

3.11 Small Intestinal Disease, Ischemia & Gastrointestinal Complications of HIV

Key Takeaways Explain This Topic AI

Bacterial overgrowth syndrome, short bowel syndrome, ischemic bowel disease, gastroenteritis and gastric bypass complications are enumerated under small intestinal disease.

Gastrointestinal complications of HIV infection form their own blueprint subsection under both Gastroenterology and Infectious Disease.

Acute mesenteric ischemia classically presents with pain out of proportion to examination findings, and a normal lactate does not exclude it early.

Terminal ileal resection causes bile-salt and vitamin B12 malabsorption, so ileal Crohn disease or resection warrants lifelong B12 monitoring.

Cytomegalovirus is the leading cause of colitis at CD4 counts below 50 cells per microliter and requires biopsy with viral inclusions for diagnosis.

Last updated: August 2026

1. Small Intestinal Bacterial Overgrowth

Excess colonic-type bacteria in the small bowel produce bloating, flatulence, diarrhea and malabsorption. It arises whenever the mechanisms that normally keep the small bowel sparsely colonized fail:

• Anatomic stasis: surgical blind loops, strictures, diverticula, adhesions
• Motility failure: diabetic autonomic neuropathy, scleroderma, chronic intestinal pseudo-obstruction
• Loss of the ileocecal valve after resection
• Achlorhydria from long-term acid suppression

The distinctive laboratory pattern is a low vitamin B12 with a normal or high folate : bacteria consume B12 while synthesizing folate. Fat malabsorption follows bacterial deconjugation of bile salts, producing steatorrhea and fat-soluble vitamin deficiency.

Diagnosis uses carbohydrate breath testing (an early hydrogen rise) or, less commonly, jejunal aspirate culture. Treatment is a course of antibiotics — rifaximin is commonly used — plus correction of the underlying anatomic or motility problem, without which recurrence is the rule.

2. Short Bowel Syndrome

Malabsorption after extensive resection. The functional consequences depend on which segment was lost, and this is the reasoning the exam tests.

• Segment lost Consequence
• Duodenum / proximal jejunum Iron, folate, calcium malabsorption
• Terminal ileum Vitamin B12 and bile salt malabsorption
• Ileocecal valve Bacterial overgrowth, faster transit
• Colon Loss of water and electrolyte salvage, loss of short-chain fatty acid energy

Terminal ileal disease or resection is the highest-yield item. Bile salts that escape ileal reabsorption enter the colon:

Limited resection (< ~100 cm): unabsorbed bile salts irritate the colon, producing bile-acid (choleretic) diarrhea that responds to a bile-acid sequestrant such as cholestyramine.

Extensive resection (> ~100 cm): the bile-salt pool is depleted, producing steatorrhea that worsens with a sequestrant and requires fat restriction and medium-chain triglycerides instead.

Giving cholestyramine to the wrong patient makes them worse — a classic distractor.

Other consequences of ileal resection: lifelong vitamin B12 supplementation , calcium oxalate kidney stones (unabsorbed fatty acids bind calcium, leaving oxalate free for absorption — enteric hyperoxaluria), and gallstone formation.

3. Post-Bariatric Complications

The blueprint lists gastric bypass complications explicitly.

Nutritional deficiencies: iron, vitamin B12, folate, thiamine, calcium, vitamin D, copper and zinc. Thiamine deficiency can present acutely as Wernicke encephalopathy after protracted post-operative vomiting and is a medical emergency.

Dumping syndrome: early (30 minutes; osmotic, with cramping, diarrhea and vasomotor symptoms) versus late (1–3 hours; reactive hyperinsulinemic hypoglycemia). Both are managed by dietary modification.

Internal hernia: intermittent postprandial pain after Roux-en-Y that can progress to closed-loop obstruction; imaging may be normal between episodes and a high index of suspicion is required.

Marginal ulceration at the gastrojejunal anastomosis, strongly associated with smoking and NSAID use.

4. Ischemic Bowel Disease

Three distinct syndromes that are frequently confused.

• Acute mesenteric ischemia Chronic mesenteric ischemia Ischemic colitis
• Vessel Superior mesenteric artery Two or more mesenteric vessels Colonic watershed
• Onset Sudden, severe Postprandial, months Subacute

Classic phrase Pain out of proportion to examination "Intestinal angina," food fear, weight loss Cramping with bloody diarrhea

Typical patient Atrial fibrillation (embolic), atherosclerosis (thrombotic), low-flow state Diffuse atherosclerosis, smoker Older, after hypotension or vascular surgery

• Diagnosis CT angiography CT/MR angiography Colonoscopy
• Treatment Emergent revascularization Revascularization Usually supportive

Acute mesenteric ischemia is the emergency. Early in its course the abdomen is soft and unimpressive while the patient reports severe pain — the discordance is the diagnosis. Lactate rises late , so a normal lactate must not be used to exclude it. Peritoneal signs indicate infarction and are a late finding. Embolic occlusion in a patient with atrial fibrillation is the classic vignette.

Ischemic colitis is far more common, involves the watershed areas (splenic flexure, rectosigmoid), and typically resolves with supportive care; the rectum is usually spared because of dual blood supply.

5. Infectious Gastroenteritis

Most acute diarrheal illness is self-limited and requires only oral rehydration. The exam focuses on when not to follow that rule.

Indications for stool testing: severe illness, fever, bloody stool, immunocompromise, recent antibiotics, hospitalization, or persistent symptoms.

Inflammatory (invasive) pathogens — Shigella , Campylobacter , Salmonella , Shiga toxin-producing Escherichia coli , Entamoeba histolytica — cause fever, bloody stool and fecal leukocytes. Non-inflammatory pathogens — norovirus, enterotoxigenic E. coli , Vibrio , preformed toxins from Staphylococcus aureus or Bacillus cereus — cause watery diarrhea without fever.

The single most important antibiotic rule: in suspected Shiga toxin-producing E. coli (including O157:H7) , antibiotics and antimotility agents are contraindicated , because they increase the risk of hemolytic uremic syndrome . Suspect it when bloody diarrhea occurs with little or no fever.

Other associations worth knowing: Campylobacter preceding Guillain-Barré syndrome ; Yersinia mimicking appendicitis with right lower quadrant pain; Vibrio vulnificus after raw shellfish, especially dangerous in iron overload and cirrhosis; and post-infectious irritable bowel syndrome after any of these.

6. Gastrointestinal Complications of HIV Infection

The likely pathogen tracks the CD4 count , and this stratification is the testable structure.

• CD4 count Diarrheal / GI pathogens and lesions
• Any count Bacterial enteritis (often more severe and bacteremic), Clostridioides difficile , medication effect
• < 200 Cryptosporidium , Microsporidia , Isospora (Cystoisospora)
• < 100 Esophageal candidiasis , HSV and CMV esophagitis
• < 50 Cytomegalovirus colitis , Mycobacterium avium complex

Esophageal disease is a common presentation:

Candida — the most common cause; oral thrush plus dysphagia justifies empiric fluconazole , with endoscopy reserved for non-responders.

Cytomegalovirus — large, solitary, linear or deep ulcers; treated with ganciclovir.

Herpes simplex virus — multiple small, shallow, well-circumscribed ulcers; treated with acyclovir.

Idiopathic aphthous ulceration — a diagnosis of exclusion treated with corticosteroids or thalidomide.

Cytomegalovirus colitis at CD4 counts below 50 causes abdominal pain, bloody diarrhea, fever and weight loss, and may perforate. Serology is inadequate for diagnosis; colonoscopic biopsy demonstrating intranuclear inclusions is required.

Chronic watery diarrhea with a normal CD4 count on suppressive antiretroviral therapy is more likely to be a medication adverse effect — protease inhibitors are the usual culprits — than an opportunistic infection. Ultimately, the definitive treatment for most HIV-associated gastrointestinal opportunistic disease is immune reconstitution with effective antiretroviral therapy ; pathogen-directed treatment alone rarely produces durable control when the CD4 count remains low.