What is the diagnosis and treatment for a 32-year-old woman with alternating constipation and diarrhea, worsening during stress and after consuming high-FODMAP (Fermentable Oligo-, Di-, Mono-saccharides, and Polyols) foods, with a history of tension headaches?

Diagnosis: Irritable Bowel Syndrome with Mixed Bowel Habits (IBS-M)

This patient meets diagnostic criteria for IBS-M based on alternating constipation and diarrhea, abdominal symptoms improved by defecation, stress-related exacerbation, and FODMAP sensitivity—all classic features that align with Rome criteria without requiring extensive testing in a young patient without alarm features. 1

Diagnostic Approach

Positive Symptom Identification

• The Rome II criteria are met: abdominal discomfort with at least 2 of 3 features: (1) relief with defecation, (2) onset with change in stool frequency, and (3) onset with change in stool form 1
• IBS-M subtype classification: alternating hard and soft stools more than 25% of the time each defines mixed-pattern IBS 1
• Stress reactivity: worsening during stress reflects the exaggerated colonic response to psychological stimuli characteristic of IBS, mediated through corticotropin-releasing factor 2
• FODMAP sensitivity: symptom aggravation with high-FODMAP foods indicates fermentable carbohydrate intolerance, seen in approximately 50% of IBS patients who report meal-related symptom exacerbation 1, 2

Associated Features Supporting Diagnosis

• Tension headaches: non-gastrointestinal symptoms including headache, lethargy, and backache are common comorbidities that improve diagnostic accuracy 1
• Age and demographics: 32-year-old woman fits the typical IBS demographic (most common in women and young people) 3

Exclusion of Alarm Features

No testing is required in this patient as she lacks red flags: no fever, weight loss, blood in stools, anemia, nocturnal symptoms, age >50 years, or family history of colon cancer 1

A basic screening panel (hemoglobin, C-reactive protein, celiac serology) is reasonable to exclude organic disease, but extensive investigation should be avoided 1, 3

Treatment Algorithm

First-Line Management

1. Patient Education and Reassurance

• Provide positive diagnosis with explanation of the brain-gut axis dysregulation and stress-reactivity mechanisms 1
• Reassure about benign prognosis and absence of structural pathology 1

2. Dietary Modification

• Low-FODMAP diet is the evidence-based first-line dietary intervention for moderate-to-severe symptoms, delivered by a specialized dietitian 1, 4
• The diet should be implemented in two phases: strict elimination (<0.5g FODMAPs per meal) for 2-3 weeks, then gradual reintroduction based on symptom response 5, 4
• Efficacy: 70-86% of IBS patients achieve significant symptom reduction with low-FODMAP diet in controlled trials 4, 6
• Avoid excessive caffeine-containing beverages 1

3. Lifestyle Modifications

• Increase physical activity, which improves IBS symptoms 1
• Establish regular toileting routine and adequate time for defecation 1
• Address sleep hygiene and stress management 1

4. Stress Management

• Brain-gut behavior therapies (cognitive behavioral therapy, gut-directed hypnotherapy, mindfulness-based stress reduction) are indicated given stress-related exacerbation 1
• These therapies are distinct from standard psychological treatments for anxiety/depression and specifically target gut symptoms 1

Second-Line Pharmacological Treatment

If first-line measures fail after 4-6 weeks:

For abdominal pain:

• Low-dose tricyclic antidepressants (TCAs) are preferred for gastrointestinal symptoms, particularly pain 1
• Antispasmodics (anticholinergics like dicyclomine or hyoscyamine) may help with cramping 1

For diarrhea-predominant episodes:

• Loperamide or codeine as needed 1
• Rifaximin 550mg three times daily for 14 days is FDA-approved for IBS-D and reduces symptoms in 41% vs 31% placebo 7

For constipation-predominant episodes:

• Osmotic laxatives (polyethylene glycol) or stimulant laxatives (senna, bisacodyl) 8
• Increase dietary fiber cautiously, as high-fiber diets may worsen abdominal discomfort in many IBS patients 1

Third-Line Considerations

If symptoms remain refractory:

• Test for small intestinal bacterial overgrowth (breath testing) 1
• Evaluate for bile acid diarrhea with SeHCAT scan or empiric bile acid sequestrant trial 3
• Consider pelvic floor dysfunction evaluation if defecatory symptoms predominate 3
• Assess for microscopic colitis with colonoscopy if persistent diarrhea 1

Critical Pitfalls to Avoid

• Do not pursue exhaustive testing in young patients without alarm features—this delays diagnosis and increases healthcare costs 1
• Do not implement low-FODMAP diet without dietitian supervision—stringent long-term restriction risks nutrient deficiency and adverse microbiota effects 5, 6
• Do not use low-dose TCAs to treat comorbid mood disorders—they are insufficient for psychological symptoms; use SSRIs instead if depression/anxiety is present 1
• Do not dismiss stress-related symptoms as "all in the head"—stress has documented physiological effects on colonic motility via CRF pathways 2
• Recognize that 60% of IBS patients report stress exacerbation, but 40% of organic disease patients do too—stress reactivity alone is not diagnostically specific 1, 2