Reye syndrome is very rare, and many disorders have similar symptoms. Other diseases and conditions that will be considered as a cause of symptoms before a diagnosis of Reye syndrome is made include:

• Metabolism problems. Most of these disorders are related to liver enzyme defects or protein and fatty metabolism problems and are usually diagnosed before a child is 3 years of age. Symptoms often include frequent low blood sugar levels (hypoglycemia), an enlarged heart, and muscle weakness. Another child in the family usually has the disorder as well.
• Effects of drugs (drug intoxication), such as aspirin.
• Poisoning, including from illegal drugs.
• Head injury that a parent or adult may not have seen or known about.
• Infection of the brain and spinal cord.
• Kidney failure.