Incidence of idiopathic intracranial hypertension (IIH) in adults and children: a 14-year population-based study

Idiopathic intracranial hypertension (IIH) is characterised by raised intracranial pressure in the absence of structural pathology and with normal cerebrospinal fluid composition. IIH is strongly associated with obesity and rising incidence has been reported in northern hemisphere countries. However, paediatric and Southern Hemisphere populations, including Australia, are under-represented in the existing literature.

We conducted a multicentre retrospective study of adults (≥ 18 years) and children (< 18 years) diagnosed with definite IIH (Revised Friedman criteria 2013) between 2010 and 2023 at two Melbourne-based quaternary hospitals, capturing the majority of cases in Victoria, Australia. Demographic and clinical data were collected at diagnosis. Annual crude and age-standardised incidence rates per 100,000 population were calculated overall and by age group across predefined periods (2010–2014, 2015–2019, and 2020–2023). Temporal trends were assessed using negative-binomial regression.

A total of 612 incident IIH cases were identified, including 504 adults and 108 children. Adults were predominantly female (94%), with mean age 28.0 ± 6.5 years and mean BMI 37.6 ± 8.4 kg/m2. Children showed lower female predominance (76%), younger mean age (12.4 ± 3.5 years), and lower mean BMI (31.9 ± 8.4 kg/m2). Headache was the most common presenting symptom in both groups (adults 84% and children 86%). Diplopia and sixth nerve palsy were more frequent in children.

Age-standardised IIH incidence increased from 0.86/100,000 person-years in 2010–2014 to 6.53/100,000 in 2020–2023. In adults, incidence rose from 0.07/100,000 in 2010 to 2.30/100,000 in 2023 (32-fold); in children, from 0.33/100,000 to 1.01/100,000 (threefold). The highest incidence rates were seen among females aged 18–39 years, in whom incidence rose from 0.11/100,000 to 6.79/100,000 between 2010 and 2023.

IIH incidence in Victoria increased substantially over 14 years, with the greatest burden among young adult females, mirroring international trends and highlighting the need for ongoing surveillance and mechanistic research.