What is the best course of management for a 15-year-old male with a history of exercise-induced asthma, gastritis, and suspected Irritable Bowel Syndrome (IBS), presenting with dizziness, nausea, and orthostatic intolerance, exacerbated by standing, with normal blood pressure and ongoing diarrhea, and no recent medication use?

Management of Orthostatic Intolerance with Gastrointestinal Symptoms in an Adolescent

This 15-year-old male has orthostatic intolerance (demonstrated by 8 bpm heart rate increase and dizziness on standing) that is likely the primary driver of his symptoms, and treating the orthostatic intolerance will likely resolve both the dizziness and potentially improve his gastrointestinal symptoms. 1, 2

Immediate Assessment and Diagnosis

The orthostatic vital signs confirm orthostatic intolerance: blood pressure dropped from 120/64 lying to 120/70 standing with heart rate increasing from 78 to 86 bpm (8 bpm increase) accompanied by dizziness at 30 seconds. 1, 3 This does not meet criteria for orthostatic hypotension (which requires ≥20 mmHg systolic or ≥10 mmHg diastolic drop), but the symptomatic heart rate increase with positional dizziness indicates orthostatic intolerance. 1, 4

The gastrointestinal symptoms (chronic diarrhea, gastritis, suspected IBS) are likely comorbid conditions rather than secondary to orthostatic intolerance, since they occur throughout the day and are not specifically triggered by standing. 5, 3 However, treating the orthostatic intolerance may still improve GI symptoms, as 78% of pediatric patients with chronic upper GI symptoms and orthostatic intolerance experience complete resolution of GI symptoms when orthostatic intolerance is treated. 2

The purulent nasal drainage and nasal congestion for one week likely represents acute bacterial sinusitis, which can contribute to dehydration and worsen orthostatic symptoms. 1

First-Line Treatment: Non-Pharmacologic Measures

Initiate aggressive volume repletion with increased salt and fluid intake immediately. 1 The American College of Cardiology/American Heart Association recommends encouraging increased salt (sodium tablets or high-sodium beverages) and fluid intake in patients with orthostatic intolerance due to dehydration. 1 Oral fluid bolus may require less volume than intravenous fluid to achieve similar treatment effect because oral fluid loading has a pressor effect. 1

• Prescribe 3-10 grams of additional dietary sodium daily (can be provided as sodium tablets or dissolved in beverages with osmolality comparable to normal body osmolality for faster rehydration). 1
• Increase total fluid intake to 2-3 liters daily, emphasizing beverages with higher sodium content. 1
• Encourage regular physical activity and exercise to avoid deconditioning, which exacerbates orthostatic intolerance. 1

Avoid medications that may cause hypotension. 1 Review all current medications (though patient denies taking any over-the-counter medications currently). 1

Treatment of Acute Sinusitis

Treat the purulent nasal drainage and nasal congestion as this likely represents acute bacterial sinusitis contributing to dehydration. Consider amoxicillin-clavulanate 875 mg twice daily for 5-7 days if symptoms persist beyond 10 days or worsen after initial improvement. This will help restore adequate hydration status.

Management of Gastrointestinal Symptoms

For the chronic diarrhea exacerbated by ramen noodles and spicy foods:

• Counsel the patient to completely eliminate ramen noodles (not just spicy foods), as he continues to consume them despite prior counseling and they clearly exacerbate his diarrhea. 6
• Identify and reduce excessive intake of lactose, fructose, sorbitol, caffeine, and alcohol, as these commonly trigger diarrhea in IBS. 6
• Start loperamide 2-4 mg as needed (maximum 12 mg daily) to control diarrhea and reduce stool frequency. 6, 7
• Add soluble fiber (ispaghula/psyllium) 3-4 g daily, gradually increased to avoid bloating, which is effective for global IBS symptoms. 6, 7
• Avoid insoluble fiber (wheat bran) as it worsens IBS symptoms. 6

For the gastritis and suspected IBS:

• Continue awaiting gastroenterology referral once insurance is activated for definitive evaluation and management. 1
• Consider a 12-week trial of probiotics for global symptoms, discontinuing if no improvement occurs. 6

Monitoring and Follow-Up

Reassess orthostatic vital signs in 2-4 weeks after initiating salt and fluid loading to determine if symptoms have improved. 1 If orthostatic intolerance persists despite adequate non-pharmacologic measures for 2-4 weeks, consider pharmacologic treatment with midodrine 2.5-5 mg three times daily (with last dose not later than 6 PM to avoid supine hypertension). 8

Review efficacy of loperamide and dietary modifications after 3 months and adjust treatment accordingly. 6 If diarrhea persists despite first-line measures, consider tricyclic antidepressants (amitriptyline 10 mg nightly, titrated slowly to 30-50 mg) as second-line therapy for both IBS symptoms and potential benefit for orthostatic intolerance. 6, 7

Critical Pitfalls to Avoid

Do not prescribe anticholinergic antispasmodics (like dicyclomine) without first determining the IBS subtype, as they can worsen constipation if the patient develops constipation-predominant symptoms. 6, 9

Do not dismiss the orthostatic intolerance as insignificant simply because blood pressure did not drop dramatically—the symptomatic heart rate increase with positional dizziness is clinically significant and requires treatment. 1, 3

Do not assume the GI symptoms are causing the orthostatic intolerance—the relationship is likely the opposite or they are comorbid conditions. 5, 3 However, treating the orthostatic intolerance may improve both symptom clusters. 2

Recognize that joint hypermobility, anxiety, and gastrointestinal issues are frequent comorbidities with orthostatic intolerance and should be screened for during follow-up. 3