A patient with chronic heart failure on high-dose furosemide is started on enteral nutrition for an inability to consume adequate oral nutrition. Despite a slow advancement to goal feeding rate, he suffers from electrolyte imbalance and peripheral neuritis. Deficiency of which vitamin should be suspected?

• A. Vitamin B12
• B. Folate
• C. Thiamin
• D. Riboflavin

Answer: (C)

Thiamin (vitamin B1) deficiency fits this scenario because high-dose loop diuretics like furosemide increase urinary loss of water-soluble vitamins, and starting enteral nutrition without adequate thiamine supplementation can precipitate deficiency. Thiamine is essential for carbohydrate metabolism as a cofactor for pyruvate dehydrogenase; without it, energy production falters, leading to weakness and neuropathy, and it can worsen heart failure symptoms (beriberi). In chronic heart failure patients on diuretics, this deficiency can present as peripheral neuritis and electrolyte disturbances during nutritional support. The other vitamins can cause neuropathy or other signs, but their deficiencies are not as directly linked to loop diuretic use and enteral feeding in this clinical context.