4-kg Unintentional Weight Loss in Medicine / Internal Medicine — 21yo Man | Gastroenterology | SMLE Q#13569

A 21-year-old man has 4 months of intensely pruritic rash on the extensor surfaces of both elbows, abdominal bloating, and non-bloody diarrhea (3–4 times/day) with 4-kg unintentional weight loss and fatigue. He has a cousin with similar symptoms on a special diet. Exam shows excoriated erythematous papulovesicular elbow lesions and pallor. Upper endoscopy shows scalloping of duodenal folds; biopsy shows subtotal villous atrophy with crypt hyperplasia and increased intraepithelial lymphocytes. Labs: hemoglobin 10.9 g/dL, serum calcium 1.9 mmol/L, mildly elevated transaminases; tissue transglutaminase IgA is positive. Ileocolonoscopy is normal. What is the most appropriate next step in management for this patient?