What is the diagnosis for a patient with episodic abdominal pain, altered bowel habits, and loose watery stools, with symptoms consistent with Irritable Bowel Syndrome (IBS)?

Diagnosis: Irritable Bowel Syndrome with Diarrhea (IBS-D)

This patient meets diagnostic criteria for Irritable Bowel Syndrome with diarrhea-predominant subtype (IBS-D) based on the Rome II criteria: episodic abdominal pain present intermittently for one year that is relieved by defecation, associated with loose/watery stools, mucus passage, and incomplete evacuation sensation, with normal examination and stable weight. 1

Diagnostic Criteria Met

The patient fulfills the Rome II diagnostic criteria requiring at least 12 weeks (need not be consecutive) in the preceding 12 months of abdominal pain with two out of three features 1:

• Pain relieved with defecation - explicitly stated in the presentation 1
• Change in stool frequency - "must pass several loose, watery stools" indicates increased frequency 1
• Change in stool form - loose, watery stools represent altered consistency 1

IBS-D Subtype Classification

This patient has diarrhea-predominant IBS (IBS-D) based on Rome criteria defining IBS-D as loose/watery stools more than 25% of the time with hard stools less than 25% of the time 1, 2. The patient's presentation of recurrent loose, watery stools with no mention of constipation clearly places her in this category 1.

Supportive Diagnostic Features Present

Multiple supportive features strengthen the IBS-D diagnosis 1:

• Mucus passage - noted occasionally in stool 1
• Incomplete evacuation sensation - explicitly described despite inability to pass more stool 1
• Crampy abdominal pain - characteristic pain quality for IBS 1
• Intermittent symptom pattern - symptoms present intermittently over one year fits the typical IBS pattern of flares lasting 2-4 days followed by remission periods 1, 3

Critical Absence of Alarm Features

The normal examination and stable body weight are crucial negative findings that support a functional diagnosis rather than organic disease 1. Key alarm features that are appropriately absent include 1, 4:

• No rectal bleeding or hematochezia 1, 4
• No documented weight loss 1, 4
• No nocturnal symptoms (not mentioned, suggesting symptoms don't wake her from sleep) 1, 3
• Normal abdominal examination 1
• Age consideration - if patient is female and under 45 years, this further supports IBS diagnosis 1, 4

Diagnostic Approach in Primary Care

A working diagnosis of IBS-D can be safely made in primary care based on typical symptoms, normal physical examination, and absence of alarm features, confirmed by observation over time 1. The one-year symptom duration satisfies the temporal requirement 1.

Recommended Initial Screening Tests

For patients under 45 years without alarm features, minimal testing is appropriate 1, 2:

• Complete blood count - to exclude anemia 1, 2
• Stool Hemoccult - screening test 1
• Consider celiac serology (IgA tissue transglutaminase) - celiac disease can present identically to IBS and has prevalence of 1:111 to 1:250 1, 2
• Stool examination for ova and parasites - if relevant travel history or geographic exposure 1, 2

When Colonoscopy Is NOT Required

For patients under 45 years with typical IBS symptoms, normal examination, stable weight, and no alarm features, colonoscopy is not indicated 1, 4. The British Society of Gastroenterology guidelines support making a positive diagnosis without extensive investigation in this clinical scenario 1.

Common Diagnostic Pitfalls to Avoid

• Do not confuse IBS-D with functional abdominal pain syndrome - the latter presents with continuous rather than intermittent pain and represents a more severe condition with poor response to conventional treatment 1
• Lactose intolerance screening is only indicated if the patient consumes substantial amounts of milk (>280 ml/day) - lactose malabsorption is found in only 10% of IBS patients and exclusion rarely cures IBS 1
• Postinfectious IBS occurs in 10-20% of cases - ask about preceding acute gastrointestinal illness 1
• Microscopic colitis should be considered in patients with diarrhea - sigmoidoscopy with biopsy is recommended for all patients with diarrhea-predominant symptoms if referred to hospital 1

Age-Specific Considerations

If this patient is over 45 years at symptom onset, colonoscopy should be performed to exclude colorectal malignancy regardless of the absence of other alarm features 1, 4. The age threshold of 45-50 years represents a critical cutoff for increased cancer risk 1, 4.