Iron deficiency anaemia and febrile convulsions: case-control study in children under 2 years

Patients, methods, and results

All 156 children aged 6-24 months admitted to Castellammare di Stabia Hospital, Naples, between 1 January 1993 and 30 June 1995 with diagnosis of febrile convulsions were enrolled in the study. They were healthy children without previous afebrile seizures or central nervous system disease. A febrile convulsion was defined as a seizure that occurred while the child had a rectal temperature of at least 38.3°C or an axillary temperature of at least 37.8°C documented either in the emergency department or in the history. Two groups of controls were selected: a random sample of children admitted to the same ward with diagnosis of respiratory and gastrointestinal infection during that period, and a group of healthy children randomly selected from the provincial birth register for an iron deficiency survey in Greater Naples during 1994.

Routine haematological investigations were performed for hospitalised patients at hospital admission and for population controls at the Department of Paediatrics of Naples. Data were collected from clinical records by two medical students unaware of the study hypothesis.

Iron deficiency anaemia was defined as the presence of haemoglobin concentration <105 g/l, mean corpuscular volume <70 fl, and serum iron concentration of <5.4 μmol/l. In our population of this age group the prevalence of anaemia is about 10%; we assumed that a prevalence of 20-25% among cases would be clinically relevant. Relative risk was calculated by odds ratio and 95% confidence interval by Cornfield's method.

No differences in distribution of gender, maternal age and education, birth weight and type of birth were found among study groups. Mean age was 15 (SD 5.6) months for cases, 12.4 (5) months for hospital controls, and 13 (2) months for population controls. Anaemia was significantly more common in cases (30%) than hospital (14%) and population (12%) controls (table 1).

Comment

The association between iron deficiency anaemia and febrile seizures has not been described before, and chance or unknown confounding are possible explanations. None the less, selection bias as well as confounding by social class do not seem likely in this study.

Fever can worsen the negative effects of anaemia or of iron deficiency on the brain and a seizure can occur as a consequence. Alternatively, anaemia can be associated with the severity of a febrile illness, and more severe cases could be more likely to get seizures. None the less, febrile seizures usually occur early in the illness, before haemoglobin concentration has a chance to drop as a result of infection.