USMLE

Vitamin A (Retinol) Deficiency and Excess

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Vitamins
  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus

Summary

Vitamin A (Retinol) imbalances include syndromes of deficiency and excess.

Vitamin A deficiency has a number of characteristic clinical findings, including night blindness (nyctalopia), bitot spots, dry scaly skin (xerosis cutis), and keratomalacia (corneal liquefaction).

Vitamin A excess is more common than deficiency, and chronic hypervitaminosis A is characterized by dry skin, joint pain, pseudotumor cerebri, and hepatomegaly. Acute vitamin A toxicity presents with nausea/vomiting and vertigo. Crucially, vitamin A is teratogenogenic, and prescription of retinol-containing drugs should be carefully considered in sexually-active and pregnant women.

Key Points

  • Vitamin A (Retinol) Deficiency
    • Usually due to fat malabsorption
      • pancreatic insufficiency (e.g. cystic fibrosis), biliary obstruction, or small-bowel resection are potential causes
    • Clinical Presentation (“skin and eyes”)
      • Night blindness (nyctalopia)
      • Corneal degeneration (keratomalacia) = liquefaction of cornea
      • Bitot spots (foamy spots) on conjunctiva
        • formed by squamous metaplasia
      • dry, scaly skin (xerosis cutis)
        • via follicular hyperkeratosis and loss of sebaceous gland function
      • Immunosuppression
        • T-cells need Vitamin A for normal maturation
  • Vitamin A (Retinol) Excess
    • Classically in young women taking isotretinoin (vitamin A derivative) for acne
    • Acute hypervitaminosis A (low-yield)
      • nausea, vomiting, vertigo, and blurred vision
    • Chronic hypervitaminosis A
      • Pseudotumor cerebri/idiopathic intracranial hypertension (IIH)
        • headache and papilledema
      • Hepatomegaly/hepatotoxicity
      • Dry skin/skin changes
      • Alopecia, hyperlipidemia, and joint pain (arthralgias) may be seen
    • Teratogenic (high-yield**)
      • ⊝ pregnancy test and two forms of contraception are required before isotretinoin is prescribed
      • Potential effects include craniofacial abnormalities (cleft palate), cardiac abnormalities (transposition of great vessels, tetralogy of fallot),posterior fossa CNS defects, and auditory defects


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