What are the next steps for managing malnutrition, malabsorption, and potential adult Refsum disease given lactose intolerance, digestive issues, and pending phytanic acid level test results?

Management of Malnutrition, Malabsorption, and Suspected Adult Refsum Disease

Given Amanda's presentation with malnutrition, malabsorption, lactose intolerance, and concern for adult Refsum disease, the immediate priority is to obtain phytanic acid levels while simultaneously pursuing a comprehensive malabsorption workup that includes celiac disease serology and upper endoscopy with duodenal biopsies, as celiac disease is the most common treatable cause of malabsorption in adults and must be excluded before attributing symptoms to rarer conditions. 1

Immediate Diagnostic Steps

Phytanic Acid Testing

• Proceed with phytanic acid level testing as requested to evaluate for adult Refsum disease, which is characterized by elevated plasma phytanic acid and presents with retinitis pigmentosa, polyneuropathy, cerebellar ataxia, and importantly, can cause malabsorption 2, 3
• Phytanic acid is the primary diagnostic marker for adult Refsum disease and should be measured in plasma 4
• Early diagnosis is critical because adult Refsum disease is one of the few tapetoretinal degenerations accessible to dietary therapy 2, 3

Celiac Disease Evaluation (Priority)

• Obtain IgA anti-tissue transglutaminase (TTG) antibody testing immediately as the preferred initial serologic test, along with total IgA level to exclude IgA deficiency 1
• If IgA deficient, obtain IgG-based tests (IgG-DGP or IgG-TG2) 5
• Schedule upper endoscopy with at least four duodenal biopsies (including one to two from the duodenal bulb and at least four from the distal duodenum) regardless of serology results, given her malabsorption symptoms 5, 1
• This must be done while she is consuming gluten-containing foods; a gluten-free diet will invalidate testing 1

Critical caveat: Celiac disease is the most common cause of villous atrophy and malabsorption in adults, but multiple other conditions can mimic it including small intestinal bacterial overgrowth, tropical sprue, Whipple's disease, and immunodeficiency syndromes 5

Comprehensive Malabsorption Workup

Laboratory Assessment

• Complete blood count to assess for anemia (common in both celiac disease and malabsorption) 5, 1
• Iron studies (ferritin, serum iron, iron-binding capacity) 5
• Vitamin B12 and folate levels (B12 malabsorption occurs with terminal ileal disease or bacterial overgrowth) 5, 6
• 25-hydroxyvitamin D and parathyroid hormone 5
• Calcium, phosphorus, magnesium 5
• Albumin to assess nutritional status 5
• Fat-soluble vitamins (A, D, E, K) given malabsorption 5

Additional Testing Based on Initial Results

• If celiac serology is negative but symptoms persist, consider lactose hydrogen breath testing to objectively confirm lactose malabsorption (21-25% yield in IBS-like presentations) 5
• Stool studies including microscopy for ova, cysts, parasites, and fat globules 5
• Consider small intestinal bacterial overgrowth testing if symptoms and initial workup suggest this 5

Management Algorithm Based on Diagnostic Findings

If Adult Refsum Disease Confirmed (Elevated Phytanic Acid)

• Initiate strict low-phytanic acid and low-phytol diet immediately 2, 3, 7
• This dietary therapy ameliorates polyneuropathy and ataxia and slows or stops other manifestations including retinal degeneration 2, 3
• Refer to dietitian experienced in phytanic acid restriction for dietary counseling 7
• The diet must be maintained lifelong and leads to rapid, stable fall in phytanemia with progressive improvement in peripheral neuropathy and cerebellar symptoms 8
• Monitor phytanic acid levels regularly to assess dietary compliance and therapeutic response 4
• Arrange ophthalmology evaluation for retinitis pigmentosa assessment 2, 3
• Screen for depression (reported in 86.2% of ARD patients) and provide psychosocial support 7

If Celiac Disease Confirmed (Positive Serology + Villous Atrophy)

• Initiate strict gluten-free diet with less than 10 mg gluten per day 1
• Most patients experience substantial improvement within days to weeks 1
• Address nutritional deficiencies identified in laboratory testing with appropriate supplementation 1
• Iron supplementation (100-200 mg daily or every other day) if iron deficient 5
• Vitamin D supplementation (50,000 IU weekly or calcitriol 0.25-2 mg daily) 5
• Other micronutrient replacement as indicated by laboratory results 5
• Follow-up serology at 6 months, 12 months, then yearly 1
• Persistently positive serology indicates ongoing gluten exposure or intestinal damage 1

If Both Conditions Excluded

• Focus on lactose restriction given documented lactose intolerance
• Consider trial of low FODMAP diet for functional digestive symptoms
• Evaluate for other causes of malabsorption listed in differential (small intestinal bacterial overgrowth, pancreatic insufficiency, inflammatory bowel disease) 5
• Ensure adequate compensatory hyperphagia (50% increase in caloric intake divided into 5-6 meals daily) if significant malabsorption persists 5

Nutritional Support During Workup

• Initiate empiric supplementation for common deficiencies while awaiting test results:
  • Multivitamin 1-2 capsules daily 5
  • Calcium and vitamin D supplementation 5
  • Consider iron supplementation if symptomatic anemia present 5
• Arrange dietitian consultation experienced in malabsorption disorders for dietary optimization 5, 7
• Monitor weight closely as serial measurements track nutritional status and treatment response 5

Important pitfall: Do not delay phytanic acid testing or celiac workup—both require specific dietary states for accurate diagnosis (phytanic acid reflects dietary intake patterns, celiac testing requires gluten consumption), and early diagnosis of either condition significantly impacts long-term outcomes 1, 2, 3