A patient on prolonged total parenteral nutrition without supplementation develops seborrheic dermatitis around the eyes, nose, and mouth, along with alopecia and paresthesias. Laboratory studies show elevated urinary organic acids including 3-hydroxyisovaleric acid. Which vitamin is deficient, and what is the underlying mechanism?

• A Pantothenic acid deficiency due to impaired CoA synthesis
• B Biotin deficiency due to impaired carboxylase recycling by biotinidase ✓
• C Riboflavin deficiency due to impaired FAD-dependent glutathione reductase
• D Vitamin B6 deficiency due to impaired PLP-dependent transamination

Explanation

The patient has biotin deficiency from TPN without supplementation. Elevated 3-hydroxyisovaleric acid reflects impaired activity of 3-methylcrotonyl-CoA carboxylase, a biotin-dependent enzyme. Biotinidase normally recycles biotin from biocytin. While the question describes deficiency from TPN (not genetic biotinidase deficiency), the biochemical hallmark of elevated 3-hydroxyisovaleric acid indicates impaired carboxylase function due to biotin lack. The dermatitis, alopecia, and neuropsychiatric symptoms are classic for biotin deficiency.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.