Idiopathic intracranial hypertension in Sweden : epidemiological studies focused on incidence and risk factors

Idiopathic intracranial hypertension (IIH) is a disorder which is not that unusual for neurologists and ophthalmologists to meet in clinical practice even though it only affects around 1 per 100,000 individuals. It gives rise to symptoms of headache and visual disturbances caused by high intracranial pressure (ICP). The first recorded patient with this disorder was described by Quicke in 1893, followed by 22 cases reported by Dandy in 1937, who later summarized the common diagnostic characteristics of the disorder (1). Even though we have known about this disorder for far more than 100 years and several studies have been performed to investigate its origin, we still don’t know what causes the increased pressure. We know that it more commonly affects females of reproductive age, in particular those who are obese. But why this is the case is not known. Several hypotheses have been suggested and studied over the years. Additionally, several risk factors that could be involved in the development of high intracranial pressure have been proposed. However, since the disorder and some of its risk factors are rare, there have been conflicting findings as to the strength of some of the proposed associations between such risk factors and IIH development. The intension of this thesis was to conduct studies investigating the incidence of IIH in Sweden as well as describing a Swedish cohort to shed light onto potential different risk factors. We used Swedish large national registers to investigate if risk factors were more common in IIH cases compared to controls prior to diagnosis. Study I is a descriptive study of all patients with a diagnosis code for IIH in Stockholm County during 2006-2013.We included 207 individuals ≥18 years of age with the diagnosis code G93.2 registered in the national patient register during these years. We validated the diagnosis coding by review of medical records and found that only 65% fulfilled the modified Dandy diagnostic criteria for IIH. The incidence was 0.65 per 100,000 individuals, in the lower range of most reported incidence studies on IIH. Among those fulfilling IIH diagnosis criteria, as reported in other studies, most patients were females (F/M ratio of 6:1) and females were slightly younger than men at time of diagnosis (mean age women 31 (CI 29-33) compared to 43 (CI 36-50) in men). These results provided the motivation to improve finding correctly diagnosed IIH patients to include in register studies. In study II we therefo