Encephalitic signs such as convulsion and coma are rare in DHF. They may, however, occur as a complication in cases of prolonged shock with severe bleeding in various organs including the brain. Water intoxication, as a result of inappropriate use of hypotonic solution to treat DHF patients with hyponatraemia, is a relatively common iatrogenic complication that leads to encephalopathy. A subtle form of seizure is occasionally observed in infants under one year of age during the febrile phase and, in some cases, is considered to be febrile convulsions since the cerebrospinal fluid is normal. Subdural effusions have been observed in some cases.

In recent years there has been an increasing number of reports of DF or DHF with unusual manifestations. Unusual central nervous system manifestations, including convulsions, spasticity, change in consciousness and transient paresis, have been observed. Some of these cases may have encephalopathy as a complication of DHF with severe disseminated intravascular coagulation that may lead to focal occlusion or haemorrhage.

Fatal cases with encephalitic manifes-tations have been reported in Indonesia, Malaysia, Myanmar, India and Puerto Rico. However, in most cases there have been no autopsies to rule out bleeding or occlusion of the blood vessels. Although limited, there is some evidence that, on rare occasions, dengue viruses may cross the blood-brain barrier and infect the CNS. Further studies are needed to identify the factors contributing to these unusual manifestations. Attention should be given to the study of underlying host factors such as convulsive disorders and concurrent diseases.

Encephalopathy associated with acute liver failure is commonly observed and renal failure usually occurs at the terminal stage. Liver enzymes are markedly elevated in these cases, with serum aspartate aminotransferase about 2-3 times higher than serum alanine aminotransferase.

Other rarely observed, unusual manifes-tations of DF/DHF include acute renal failure and haemolytic uraemic syndrome. Some of these cases have been observed in patients with underlying host factors (e.g. G6P deficiency and haemoglobinopathy) that lead to intravascular haemolysis. Dual infections with other endemic diseases, such as leptospirosis, viral hepatitis B, and melioidosis, have been reported in cases with unusual manifestations.