What are the first symptoms of Reye's syndrome?

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From the Guidelines

The first symptoms of Reye's syndrome are typically characterized by protracted vomiting, followed by lethargy, which is usually the first neurological manifestation, and may also include diarrhea and hyperventilation in children younger than two years. According to the study published in Thorax in 2007 1, Reye’s syndrome is marked by an acute non-inflammatory encephalopathy with an altered level of consciousness, elevation of ammonia levels, and hepatic dysfunction. The neurological symptoms usually occur 24–48 hours after the onset of vomiting. Key early signs include:

  • Protracted vomiting
  • Lethargy
  • Diarrhea and hyperventilation in children younger than two years
  • Unusual drowsiness
  • Confusion, irritability, combativeness, and disorientation as the condition progresses. It is essential to seek immediate medical attention if these symptoms appear, as Reye's syndrome can rapidly progress to seizures, coma, and potentially death 1.

From the FDA Drug Label

Children and teenagers who have or are recovering from chicken pox or flu-like symptoms should not use this product, if changes in behavior with nausea and vomiting occur, consult a doctor because these symptoms could be an early sign of Reyes syndrome, a rare but serious illness The first symptoms of Reye's syndrome are changes in behavior, nausea, and vomiting 2.

From the Research

Symptoms of Reye's Syndrome

The first symptoms of Reye's syndrome can vary depending on the age of the patient.

  • In children and adolescents, the symptoms typically start with a prodromal viral illness, such as influenza A or B or chicken pox, followed by:
    • Protracted vomiting
    • Neurologic changes, which can occur 3 to 5 days after the initial illness, when the child seems to be recovering 3, 4, 5
  • In infants, the symptoms may be more subtle and can include:
    • Diarrhea
    • Respiratory disturbances
    • Seizures 3
  • Other symptoms that have been reported in patients with Reye's syndrome include:
    • Encephalopathy
    • Fatty degeneration of the liver
    • Cerebral edema
    • Hypoglycemia 6, 7

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Reye's syndrome: an update.

The Nurse practitioner, 1997

Research

Reye's syndrome: a clinical review.

Canadian Medical Association journal, 1981

Research

Reye's syndrome: review and update.

Journal of pediatric health care : official publication of National Association of Pediatric Nurse Associates & Practitioners, 1989

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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