Is well-formed, normal-colored stool with no other abdominal symptoms and night blindness indicative of malabsorption with no other symptoms?

Is Well-Formed Stool with Night Blindness Indicative of Malabsorption?

Yes, night blindness alone with otherwise normal-appearing stools can indicate malabsorption, specifically fat-soluble vitamin A deficiency from conditions like small intestinal bacterial overgrowth (SIBO) or other malabsorptive disorders. The absence of diarrhea or steatorrhea does not exclude malabsorption.

Why This Presentation Suggests Malabsorption

Night blindness is a specific clinical manifestation of vitamin A deficiency, which occurs when bacterial overgrowth causes bile salt deconjugation and pancreatic enzyme degradation, leading to fat-soluble vitamin malabsorption even without overt steatorrhea. 1

• Vitamin A deficiency presents with night blindness, poor color vision, dry flaky skin, and xerophthalmia as the earliest and most specific symptoms 1, 2
• The combination of dilated gut with reduced propulsion and ineffective migrating myoelectric complex allows anaerobic bacteria to proliferate, causing malabsorption of fat-soluble vitamins A and E (less commonly D and K) 1
• Stool appearance can remain well-formed and normal-colored despite significant malabsorption, particularly in early SIBO or when bacterial overgrowth affects vitamin absorption without causing frank steatorrhea 2

Clinical Cases Supporting This Presentation

Multiple case reports document night blindness as the presenting symptom of malabsorption with intestinal disease:

• A patient with duodenal diverticulosis and bacterial overgrowth presented with night blindness from vitamin A deficiency, with resolution after treating bacterial overgrowth and vitamin A supplementation 3
• Patients with Crohn's disease and bowel resections developed progressive night blindness with markedly depleted vitamin A levels (11 µg/dL, reference 20-120 µg/dL) 4
• Post-bariatric surgery patients developed vitamin A deficiency retinopathy with night blindness as the primary symptom, with median duration of 14 months before diagnosis 5

Diagnostic Workup Required

Check serum vitamin A (retinol) levels immediately in any patient presenting with night blindness, regardless of stool appearance. 2, 6

Additional testing to identify the underlying cause:

• Confirm SIBO diagnosis through hydrogen and methane breath testing or small bowel aspiration during upper endoscopy 2
• Screen for other fat-soluble vitamin deficiencies: serum 25-hydroxyvitamin D, alpha-tocopherol (vitamin E), and vitamin K1/PIVKA-II levels 2, 7
• Evaluate for other malabsorptive conditions: celiac serology, fecal calprotectin (if age <45), complete blood count, C-reactive protein, and albumin 1
• Consider bile acid malabsorption testing with 23-seleno-25-homotaurocholic acid scanning or serum 7α-hydroxy-4-cholesten-3-one if there is history of cholecystectomy or atypical features 1

Critical Clinical Pitfalls

Do not wait for diarrhea or obvious steatorrhea to investigate malabsorption when night blindness is present. Several important caveats:

• Vitamin A deficiency can occur with serum retinol levels as low as 0.21 µmol/L while maintaining relatively normal stool appearance 8
• Rod-mediated vision (night vision) is affected before cone function, making night blindness the earliest symptom 8
• Bacterial overgrowth can manufacture vitamin K and folic acid, potentially masking other signs of malabsorption with normal or elevated levels of these vitamins 1
• The absence of weight loss does not exclude malabsorption, as vitamin deficiencies can develop before significant nutritional compromise 2

Management Approach

Once vitamin A deficiency is confirmed:

• Begin supplementation with water-miscible vitamin A at 10,000 IU (3000 µg) daily, adjusting based on follow-up laboratory testing 1, 2
• Treat underlying SIBO if confirmed, as correction of bacterial overgrowth is essential for long-term resolution 3
• Monitor vitamin A levels at 3-month intervals initially, then every 6 months once stabilized 2, 7
• Serum retinol levels of 0.7 µmol/L or higher are required for normal dark-adapted rod sensitivity, though normal time-course of rod adaptation may require levels >0.95 µmol/L 8
• Consider intramuscular vitamin A if oral supplementation fails to correct deficiency 4, 5