Deficiency syndromes of fat-soluble vitamins

Vitamin A Deficiency - Night Blindness Blues

• Function: Vision (retinal cycle), immune health, and differentiation of epithelial cells. Stored in stellate (Ito) cells of the liver.
• Causes: Malnutrition, fat malabsorption (e.g., celiac disease, cystic fibrosis), or liver disease.
• Ocular Signs (Xerophthalmia):
  • Nyctalopia (night blindness) is the earliest symptom.
  • Bitot's spots: White, foamy plaques of keratin on the conjunctiva.
  • Keratomalacia: Corneal softening, ulceration, leading to irreversible blindness.
• Other Effects: Follicular hyperkeratosis, impaired immunity (↑ risk of measles morbidity).

⭐ Deficiency leads to squamous metaplasia of epithelial linings (e.g., respiratory, urinary tracts), replacing normal mucus-secreting epithelium with keratinized squamous cells.

Vitamin D Deficiency - Brittle Bones Breakdown

• Pathophysiology: Insufficient UV light or dietary intake → ↓ calcitriol (1,25-dihydroxyvitamin D) → impaired intestinal absorption of Ca²⁺ & PO₄³⁻.
• Syndromes:
  • Rickets (Children): Defective mineralization of cartilaginous growth plates.
    • Bowed legs (genu varum), rachitic rosary (costochondral hypertrophy), craniotabes.
  • Osteomalacia (Adults): Defective mineralization of existing bone.
    • Diffuse bone pain, muscle weakness, ↑ fracture risk.
• Labs: ↓ Ca²⁺, ↓ PO₄³⁻, ↑ PTH (secondary hyperparathyroidism), ↑ alkaline phosphatase.

⭐ On X-ray, osteomalacia classically presents with Looser zones (pseudofractures)-radiolucent bands perpendicular to the cortex, especially in the scapula, pelvis, or femoral neck.

Vitamin E Deficiency - Nerve & RBC Wreck

• Function: Potent lipid-soluble antioxidant. Protects RBC and neuronal cell membranes from free radical-induced oxidative damage.
• Causes: Rare. Primarily from fat malabsorption syndromes (cystic fibrosis, cholestasis) or abetalipoproteinemia.
• Clinical Presentation:
  • Hemolytic anemia: Increased RBC fragility leads to acanthocytosis (spur cells) and a shortened RBC lifespan.
  • Neurologic Dysfunction: Due to demyelination of posterior columns and spinocerebellar tracts.
    • Ataxia
    • Peripheral neuropathy
    • Loss of proprioception and vibration sense
  • Retinopathy: Pigmentary changes that can mimic retinitis pigmentosa.

⭐ Neurologic symptoms can closely mimic Friedreich ataxia. Differentiate by the absence of hypertrophic cardiomyopathy and skeletal deformities (e.g., scoliosis) in Vitamin E deficiency.

Vitamin K Deficiency - The Bleeding Problem

• Function: Essential cofactor for γ-glutamyl carboxylase, which activates clotting factors II, VII, IX, X and anticoagulant proteins C & S.
• Etiology: Malabsorption (Crohn's, cystic fibrosis), broad-spectrum antibiotics (↓ gut flora), and newborns (sterile gut, poor placental transfer).
• Labs & Clinical: ↑ PT is the earliest indicator (Factor VII's short half-life), later followed by ↑ aPTT. Normal bleeding time. Presents with easy bruising, mucosal bleeding, melena, and hematuria.

⭐ Warfarin acts as a Vitamin K antagonist by inhibiting the enzyme Vitamin K epoxide reductase, preventing the regeneration of active Vitamin K.

High‑Yield Points - ⚡ Biggest Takeaways

• Vitamin A deficiency presents with night blindness, xerophthalmia (dry eyes), and corneal Bitot spots.
• Vitamin D deficiency causes rickets in children and osteomalacia in adults, leading to defective bone mineralization.
• Vitamin E deficiency can cause hemolytic anemia and neurologic dysfunction (e.g., spinocerebellar ataxia).
• Vitamin K deficiency impairs clotting factor synthesis, causing a prolonged PT/INR and bleeding risk.
• Deficiencies are common in fat malabsorption syndromes like cystic fibrosis and cholestasis.