Fever and convulsions in infancy

A significant number of little children experience convulsive activity during episodes of infective and other fevers. Lorin (1982) suggests that 2–4% of all children have at least one fever-related seizure by the age of 5–7 years. Others (e.g. Miller et al., 1960), have given a figure of 33/1000, or 3.3%, during the first five years of life. American studies tend to report a slightly higher incidence. While there is still some argument on the subject it seems likely that there is a genetic factor, a specific genetic trait transmitted by a low penetrance single dominant gene, in the predisposition to febrile convulsions in many cases (for review see Lennox-Buchtal, 1976). The distribution of the temperatures at which convulsions occur was studied by Herlitz (1941), and it was slightly skewed from a Gaussian distribution with a peak incidence at 39.5–40.5 °C. This distribution is shown in Fig. 8.1. Some children convulse in response to small increases in body temperature in mild infections and these seizures can be severe. There may be a relationship between the rate of body temperature rise and the development of seizures. There is little evidence concerning a possible mechanism for the triggering of febrile convulsions in children, and the animal models, which are few, do not include spontaneous convulsions in response to infectious fevers and are thus not entirely satisfactory.

There may be serious sequelae to febrile convulsions though, fortunately, most single or even double episodes have a benign long-term outcome.