Growing numbers of people are developing a potentially blinding type of weight-linked headache, idiopathic intracranial hypertension (IIH), that was once considered rare. In the study, IIH rates increased sixfold in Wales between 2003 and 2017 - from 12 per 100,000 people to 76 per 100,000 people. During the same 15-year span, obesity rates in Wales rose from 29% of the population to 40%. The findings were reported in the paper, ‘Incidence, Prevalence and Healthcare Outcomes in Idiopathic Intracranial Hypertension: A Population Study’, published in Neurology.
"The considerable increase in IIH incidence" has several causes, but is likely "predominately due to rising obesity rates," said study author, Dr William Owen Pickrell, a consultant neurologist at Swansea University. "The worldwide prevalence of obesity nearly tripled between 1975 and 2016, and therefore, these results also have global relevance."
IIH is a type of headache that occurs when the fluid around your brain and spinal cord builds up in your skull. This places extra pressure on your brain and the optic nerve in the back of your eye, causing symptoms that can mimic a brain tumour such as debilitating head pain, blind spots and possibly vision loss, according to the National Eye Institute.
The cause is not fully understood, but weight loss is the main treatment. Some people may need medication and/or surgery to drain the fluid and relieve the pressure.
The researchers 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. They recorded body mass index (BMI), deprivation quintile, CSF diversion surgery and unscheduled hospital admissions in case and control cohorts.
They reported that 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/year, a significant increase from 2003 (corresponding figures=12/100,000 and 2.3/100,000/year) (p<0.001). They also noted that 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 gender and BMI, was 0.65 (95% CI 0.55 to 0.76).
A total of 9% 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).
"There is some evidence that weight loss can improve headache symptoms," Pickrell said, adding that there could be explanations other than obesity for the surge in IIH.
"The increase may also be attributable to increased IIH diagnosis rates due to raised awareness of the condition and greater use of [digital] technology at routine optometry appointments," he said. Eye doctors often diagnose IIH during routine exams that look at the back of the eye.
The biggest concern with these headaches is the potential for vision loss, which likely explains the increased rates of emergency hospital admissions seen in the new study among people with IIH.