Hypervitaminosis A

Hypervitaminosis A is the toxic state resulting from the excessive ingestion of preformed Vitamin A (retinol or retinyl esters). Unlike water-soluble vitamins, Vitamin A is stored in the liver, and its capacity for storage can be exceeded, leading to toxicity. It has a relatively narrow therapeutic window compared to other vitamins.

Etiology and Pathogenesis

• Source of Toxicity: Toxicity is caused exclusively by preformed Vitamin A (found in liver, fish liver oils, therapeutic supplements, and fortified foods).
• Carotenoids: Precursors like beta-carotene (found in vegetables) do not cause hypervitaminosis A because their conversion to retinol is physiologically regulated.
• Mechanism: When hepatic storage capacity is exceeded, free retinol circulates in the blood (unbound to Retinol Binding Protein), causing cellular damage by disrupting lysosomal membranes.
• "Gulf Syndrome": A historical term referring to hypervitaminosis A and D observed in children due to excessive intake of attractive fish oil pearls brought from Middle-East countries.

1. Acute Hypervitaminosis A

This occurs following the ingestion of a massive dose of Vitamin A over a short period.

• Clinical Features:
  • CNS (Pseudotumor Cerebri): Signs of increased intracranial pressure are prominent.
    • Bulging anterior fontanelle in infants,.
    • Severe headache, vomiting, and irritability.
    • Diplopia and papilledema.
    • Stupor and vertigo.
  • Gastrointestinal: Nausea, vomiting, and abdominal pain are early signs,.
  • Skin: Desquamation (peeling) of the skin may occur later during recovery.

2. Chronic Hypervitaminosis A

Chronic toxicity results from the daily ingestion of doses exceeding the physiologic requirement over weeks or months.

• Toxic Dosage: Chronic daily intakes of >6,000 µg (~20,000 IU) in children can be toxic.
• Latent Period: Symptoms typically appear after a latent period of weeks to months depending on the dose and liver storage status.

Clinical Manifestations

• General Systemic Symptoms:
  • Anorexia and weight loss (failure to thrive).
  • Irritability and fatigue.
  • Low-grade fever.
• Dermatological Changes:
  • Pruritus: Dry, itchy skin is common.
  • Desquamation: Peeling of the skin, particularly on the palms and soles.
  • Mucocutaneous: Fissures at the corners of the mouth (cheilitis) and dry mucous membranes.
  • Hair: Alopecia (hair loss) and coarsening of the hair,.
• Musculoskeletal System:
  • Bone Pain: Deep bone pain and tenderness, often causing limitation of motion.
  • Cortical Hyperostosis: Painful soft tissue swellings over long bones (especially the ulna and tibia) due to new bone formation,,.
  • Premature Epiphyseal Fusion: Can lead to growth arrest and short stature.
• Hepatic Involvement:
  • Hepatomegaly and splenomegaly,.
  • Can progress to cirrhosis, portal hypertension, and ascites in severe cases.
• Neurological:
  • Pseudotumor cerebri (Benign Intracranial Hypertension) causing headache and diplopia,.

3. Teratogenicity

• Vitamin A is a known teratogen. High doses taken during early pregnancy (first trimester) can cause severe congenital malformations.
• Defects: Craniofacial abnormalities (cleft palate), CNS defects, and thymic abnormalities,.
• Isotretinoin: Synthetic retinoids used for acne (e.g., Accutane) are highly teratogenic.
• Safety Limit: Intake during pregnancy should not exceed 10,000 IU/day,.

4. Carotenemia (Differential Diagnosis)

• Definition: Yellow-orange pigmentation of the skin caused by excessive intake of carotene-rich foods (carrots, papaya, squash).
• Safety: It is benign and does not lead to vitamin A toxicity,.
• Clinical Features:
  • Yellowing is prominent in the nasolabial folds, palms, and soles,.
  • Sclera is spared: Unlike jaundice, the sclera remains white.
• Management: Resolves slowly upon reducing intake of carotene-rich foods.

Diagnosis

• History: Detailed dietary history revealing excessive intake of supplements (fish liver oil, vitamin pearls) or liver.
• Serum Vitamin A Levels:
  • Elevated serum retinol levels (often >100 µg/dL).
  • Presence of retinyl esters in circulation (normally absent).
• Radiology (X-ray):
  • Hyperostosis: Cortical thickening of long bones (typically ulna, tibia, and metatarsals),.
  • The hyperostosis is typically in the middle of the shafts (diaphysis).
  • Metaphyseal changes may be absent (distinguishing it from other conditions like infantile cortical hyperostosis).
• Biochemistry: Hypercalcemia and elevated alkaline phosphatase may be present.

Management

• Cessation of Intake: The primary treatment is the immediate withdrawal of the source of Vitamin A.
• Prognosis:
  • Systemic symptoms (vomiting, anorexia) usually subside rapidly.
  • Skin and hair changes resolve over weeks.
  • Hyperostosis and bone remodeling may take several months to resolve.
• Supportive Care: Management of raised intracranial pressure or hypercalcemia if present.