What could be causing night blindness, difficulty with vision, back pain, and recent diarrhea in a 15-year-old female with a history of night blindness since childhood?

Vitamin A Deficiency from Malabsorption Syndrome

This 15-year-old female most likely has vitamin A deficiency secondary to chronic malabsorption, evidenced by lifelong night blindness now progressing to worsening vision, with recent diarrhea and back pain suggesting an underlying gastrointestinal disorder causing fat-soluble vitamin malabsorption.

Primary Diagnosis: Vitamin A Deficiency

The clinical presentation is classic for progressive vitamin A deficiency:

• Night blindness since childhood represents the earliest and hallmark symptom, resulting from insufficient rhodopsin synthesis in retinal photoreceptors 1, 2, 3
• Progressive vision difficulty indicates advancing xerophthalmia and potential corneal involvement 2, 3
• Recent diarrhea strongly suggests an underlying malabsorption syndrome as the root cause 2, 4

Underlying Etiology: Malabsorption Syndrome

The combination of chronic night blindness with recent diarrhea points to a gastrointestinal disorder causing fat malabsorption:

• Celiac disease is a leading consideration in adolescents with chronic malabsorption and vitamin A deficiency 2
• Crohn's disease commonly presents with diarrhea, back pain (from inflammatory arthropathy), and vitamin A deficiency 5
• Chronic pancreatitis can cause both back pain and fat-soluble vitamin malabsorption 6
• Small intestinal bacterial overgrowth (SIBO) causes diarrhea and vitamin A deficiency through bile salt deconjugation 4

The back pain may represent:

• Inflammatory arthropathy associated with inflammatory bowel disease 5
• Vertebral bone pain from concurrent vitamin D deficiency 4
• Referred pain from pancreatic pathology 6

Diagnostic Approach

Immediate Laboratory Testing

• Serum retinol (vitamin A) level - expect <200 ng/mL (normal 400-700 ng/mL) 6, 5
• Complete blood count - assess for anemia from malabsorption 4
• Comprehensive metabolic panel - evaluate liver function and electrolytes 2
• Prothrombin time/INR - screen for vitamin K deficiency 4
• 25-hydroxyvitamin D level - commonly co-deficient with vitamin A 4
• Tissue transglutaminase IgA with total IgA - screen for celiac disease 2
• Fecal calprotectin - evaluate for inflammatory bowel disease 5

Ophthalmologic Evaluation

• Dark adaptation testing - will show reduced adaptation to <1 log unit 6
• Electroretinography (ERG) - scotopic responses will be extinguished or severely reduced 6, 5
• Slit lamp examination - assess for Bitot spots, corneal xerosis, or keratomalacia 2, 3

Critical Pitfall

Serum retinol levels may remain falsely normal despite depleted hepatic stores, particularly in chronic liver disease or during acute inflammation 2. However, given the severe clinical presentation with lifelong night blindness, testing will likely reveal markedly depleted levels 6, 5.

Immediate Treatment Protocol

Vitamin A Supplementation

Begin oral vitamin A 10,000-25,000 IU daily immediately 3, 4:

• For severe night blindness with progressive vision loss, start at 25,000 IU daily 3
• If malabsorption is severe or patient cannot tolerate oral therapy, consider intramuscular vitamin A 50,000 IU 5
• Water-miscible formulations are preferred in malabsorption syndromes for improved absorption 4
• Clinical improvement in night blindness should occur within 7 days of adequate supplementation 6

Concurrent Fat-Soluble Vitamin Replacement

Given malabsorption etiology, replace all fat-soluble vitamins simultaneously 4:

• Vitamin D: 3,000 IU daily (titrate based on 25-OH vitamin D levels) 4
• Vitamin E: 100 IU daily (if neuropathy present) 4
• Vitamin K: 300 mcg daily (if coagulopathy present) 4

Monitoring

• Recheck serum vitamin A level after 3 months of supplementation 3
• Repeat ERG testing once vitamin A normalized to document functional recovery 6, 5
• Monitor every 6 months if chronic malabsorption persists 4

Treatment of Underlying Malabsorption

The definitive treatment requires identifying and managing the underlying gastrointestinal disorder:

• If celiac disease confirmed: strict gluten-free diet with continued vitamin supplementation 2
• If Crohn's disease diagnosed: immunosuppressive therapy per gastroenterology, with ongoing vitamin monitoring 5
• If SIBO identified: rifaximin 550 mg three times daily for 14 days, with repeat breath testing 4
• If chronic pancreatitis: pancreatic enzyme replacement therapy 6

Critical Safety Considerations

Avoid Vitamin A Toxicity

• Do not exceed 25,000 IU daily for prolonged periods without monitoring 3
• Upper limit is 10,000 IU daily for women of childbearing age due to teratogenic risk 3
• Signs of toxicity include hepatomegaly, alopecia, increased intracranial pressure, and hypercalcemia 1

Urgent Ophthalmology Referral

Refer immediately to ophthalmology if any of the following are present 1:

• Corneal clouding or ulceration (keratomalacia) 2, 3
• Severe vision loss beyond night blindness 3
• Any structural corneal abnormality on examination 2

Keratomalacia can progress to permanent blindness within days without treatment 2, 3.

Prognosis

• Night blindness is completely reversible with adequate vitamin A replacement if corneal damage has not occurred 6, 5
• Scotopic ERG responses normalize within weeks of vitamin A repletion 6, 5
• Permanent blindness results only if keratomalacia progresses to corneal perforation and scarring 2, 3
• Long-term prognosis depends on successful management of the underlying malabsorption disorder 4, 5