Incidence, Prevalence, and Health Care Outcomes in Idiopathic Intracranial Hypertension: A Population Study

Abstract

Objective: To characterize trends in incidence, prevalence, and health care outcomes in the idiopathic intracranial hypertension (IIH) population in Wales using routinely collected health care data.

Methods: We used and validated primary and secondary care IIH diagnosis codes within the Secure Anonymised Information Linkage databank to ascertain IIH cases and controls in a retrospective cohort study between 2003 and 2017. We recorded body mass index (BMI), deprivation quintile, CSF diversion surgery, and unscheduled hospital admissions in case and control cohorts.

Results: We analyzed 35 million patient-years of data. There were 1,765 cases of IIH in 2017 (85% female). The prevalence and incidence of IIH in 2017 was 76/100,000 and 7.8/100,000/y, a significant increase from 2003 (corresponding figures = 12/100,000 and 2.3/100,000/y) (p < 0.001). IIH prevalence is associated with increasing BMI and increasing deprivation. The odds ratio for developing IIH in the least deprived quintile compared to the most deprived quintile, adjusted for sex and BMI, was 0.65 (95% confidence interval 0.55 to 0.76). Nine percent of IIH cases had CSF shunts with less than 0.2% having bariatric surgery. Unscheduled hospital admissions were higher in the IIH cohort compared to controls (rate ratio 5.28, p < 0.001) and in individuals with IIH and CSF shunts compared to those without shunts (rate ratio 2.02, p < 0.01).

Conclusions: IIH incidence and prevalence is increasing considerably, corresponding to population increases in BMI, and is associated with increased deprivation. This has important implications for health care professionals and policy makers given the comorbidities, complications, and increased health care utilization associated with IIH.

Figure 1. Body Mass Index (BMI) at Diagnosis for the Idiopathic Intracranial Hypertension (IIH) Cohort

The distribution of BMI measurements at nearest IIH diagnosis for women (ochre) and men (blue). The y-axis shows the proportion of either all female or all male cases.

Figure 2. Prevalence and Incidence of Idiopathic Intracranial Hypertension (IIH) Compared With Obesity (2003–2017)

Changes in (A) IIH prevalence and (B) IIH incidence with time during the study period. Ochre lines represent the female population, blue lines represent the male population, and green lines represent the combined population. (C) Changes in the proportion of the population who are obese (body mass index >30 kg/m²) from general practitioner (GP) BMI measurements (red line), National Survey for Wales (NSW) data (green line), and a mean average of the two (blue line) during the study period. The x-axis in all graphs represents time in years. Note NSW data were not available for 2003–2005 or 2015–2017.

Figure 3. Choropleths Comparing Welsh Idiopathic Intracranial Hypertension (IIH) Incidence and Prevalence With Deprivation

(A) Map of the current Welsh health boards. Choropleth maps show the distribution of (B) deprivation, measured as a percentage of the health board population in the 2 most deprived Welsh Index of Multiple Deprivation (WIMD) quintiles (1–2); (C) IIH incidence 2015–2017 by the health board; and (D) IIH prevalence in 2017 by the health board. Data for the Powys Health board could not be presented for incidence and prevalence due to restrictions in obtaining small numbers from Secure Anonymised Information Linkage. See also table e-8 (zenodo.org/record/4064064). NHS = National Health Service.

Figure 4. Relationship of Idiopathic Intracranial Hypertension (IIH) Prevalence and Incidence With Obesity and Deprivation

Association between IIH prevalence (A) and incidence (B) with body mass index (BMI). BMI <20 kg/m² is defined as underweight, 20 kg/m² < BMI < 25 kg/m² normal weight, 25 kg/m² < BMI < 30 kg/m² overweight, and BMI >30 kg/m² as obese. (C, D) Relationship between IIH prevalence and incidence with deprivation as measured by the Welsh Index of Multiple Deprivation (1 = most deprived, 5 = least deprived). (E) Relationship between obesity and deprivation for 2015 (similar relationships exist for other study years; see figure e-2, zenodo.org/record/4064064). The green line is obtained from primary care BMI measurements, the blue line from Welsh Health Survey BMI data, and the red line is the mean of the 2 measurements. GP = general practitioner; NSW = National Survey for Wales.

Figure 5. Rates of Unscheduled Hospital Visits Among 3 Cohorts

Rates of unscheduled hospital visits (per person per year) versus time since idiopathic intracranial hypertension (IIH) diagnosis in months. A negative value indicates time before the diagnosis and a positive value indicates time after the diagnosis. Green line represents the IIH cohort; red line represents the control cohort (matched on age, sex, and deprivation quintile); blue line represents the IIH cohort with CSF diversion surgery (CSF shunts).