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Reye's syndrome is an extremely serious acute condition that may attack all major organs of the body, but particularly the brain and liver. Rapid buildup of fatty deposits in the liver can cause liver failure, but what makes Reye's so dangerous is inflammation of the brain. Reye's syndrome usually affects children between 4 and 12 years of age, although it has also been observed in adults.

Fortunately, Reye's syndrome is very rare and becoming rarer. Between 1974 and 1984 it affected between 200 and 550 children in the Unites States every year. It now affects only about 20 people a year. Most of these are children who have taken acetylsalicylic acid* (ASA) for the flu, another respiratory infection, or chickenpox.

It's widely believed that the drop in cases is directly due to the replacement of ASA with acetaminophen among children and adolescents.

Nobody knows what causes Reye's syndrome. Most cases of Reye's syndrome occur after a viral infection such as chickenpox or influenza and are concentrated around the flu season, in late fall and winter.

The disease was first classified in 1963, when it was noted that the vast majority of victims had been taking ASA or other products containing salicylates in the days before Reye's developed. Since then, research has failed to find any other risk factor. We do know that Reye's syndrome is not contagious.

Reye's syndrome usually occurs during or after a viral infection involving the airways. In most cases, the viral infection and fever will already be fading, though occasionally Reye's appears just a few days into the infection.

The first symptom is continuous and violent vomiting and dry retching. The other clear warning sign is a change in mental status due to brain inflammation. In the early stages or in a milder case, lethargy and confusion are prominent. People may become aggressive, striking out at would-be helpers. In the final stages, muscles may become stiff or lose function and seizures, loss of reflexes, difficulty breathing, and coma may occur.

Although rare, Reye's syndrome should be considered if a child with an upper respiratory tract infection starts vomiting constantly and exhibits confusion or lack of responsiveness.

Early diagnosis is crucial. A doctor who suspects Reye's will look for elevated ammonia levels in the blood, and will perform liver function tests. Results usually take 2 to 3 hours to arrive.

Spinal tap or lumbar puncture tests may be tried. This won't detect Reye's, but it's important to eliminate the possibility of meningitis, which is a far more common disease.

There's no cure for Reye's syndrome, since the cause of the illness is unknown. In many cases, the first step is an intravenous glucose solution, as low blood sugar is a risk. It's also important to prevent brain damage by controlling the pressure in the brain from reaching dangerous levels. In mildly affected people, the disease will pass within a week.

Other common treatments include:

• insertion of an tube into the child's throat attached to a ventilator machine to assist the child's breathing
• vitamin K and blood products to help with bleeding
• medications such as dexamethasone or mannitol to control the pressure in the brain due to swelling

After a bout with Reye's syndrome, brain damage may occur. While many people are unharmed by the condition, evidence of neurologic damage is common. Brain scans such as electroencephalograms (EEGs) may show signs of damage that may or may not be reflected in the person's behaviour or intellectual capacity. Children in particular can sustain physical damage to the brain without losing any capability.

It's worth remembering that lightning strikes kill more people than Reye's syndrome. Even if a child is given ASA to combat the flu, the child is at extremely low risk. Nevertheless, taking ASA is the only known risk factor. Taking ASA to fight respiratory viruses increases the risk up to 35 times.

While only ASA itself has been clearly linked to Reye's, the US National Reye's Syndrome Foundation recommends that (pending further research) the whole salicylate family of medications should be avoided during viral illness. If you're not sure, consult your doctor.

*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For more information on brand names, speak with your doctor or pharmacist.