Idiopathic Intracranial Hypertension More Likely to Cause Vision Loss in Blacks

Caroline Cassels

March 13, 2008

March 13, 2008 — African Americans with idiopathic intracranial hypertension (IIH) are more likely than members of other ethnic groups to experience vision loss, new research suggests.

A retrospective study showed that black patients with IIH were 3.5 times more likely to have severe vision loss in at least 1 eye and were nearly 5 times as likely to become legally blind than nonblack patients.

"African Americans had a much more severe risk of visual loss than whites. We looked at potential differences in care, such as disparities in access to neuroimaging and treatment, but this appeared not to be a factor," study author Beau Bruce, MD, Emory University School of Medicine, in Atlanta, Georgia, told Medscape Neurology & Neurosurgery.

"In fact," he added, "in many cases black patients were diagnosed more frequently and had higher rates of surgery and so were treated very aggressively, so there was no reason to suspect there's anything different about the way we care for African American patients vs other ethnic groups. This finding suggests there is something different about the way this disease behaves in blacks."

The study is published in the March 11 issue of Neurology.

Obesity A Growing Concern

Although a rare condition, IIH is relatively common in young, obese women regardless of ethnic background. Dr. Bruce said that research shows that, in the general population, IIH occurs in about 1 per 100,000. In females, it is about 1.6 per 100,000. However, there is a marked rise in prevalence to 8 per 100,000 among women aged 15 to 44 years with a body-mass index (BMI) greater than 26.

Furthermore, there is a strong association between obesity and the condition. Given growing obesity rates in the United States and other countries, there is a concern, said Dr. Bruce, that there will also be a concomitant rise in IIH, which can also occur in children.

While some smaller studies have suggested that black patients may have more severe outcomes, few studies have looked specifically racial differences in IIH. As a result, said Dr. Bruce the aim of the current research was to evaluate racial differences in this disease, which results in severe vision loss in up to 10% of patients.

"As far as I know, this is the only study that has specifically addressed the issue of race in this disease," he said.

For the study, researchers reviewed the medical records of all patients at Emory University with IIH over a 17-year period, from 1989 to 2006. Of the 450 subjects, 197 were black, 246 were white, 5 were Hispanic, and 2 were Asian.

Although the study was a retrospective chart review, all patients had undergone a standardized evaluation by an experienced neuro-ophthalmologist.

Data were also gathered on demographics; relevant risk factors, including medication use, the presence or absence of recent weight gain, sleep apnea, anemia, systemic hypertension, endocrine disorders, and pregnancy; and associated symptoms such as headache, tinnitus, double vision, and transient visual loss.

In addition, all subjects had undergone lumbar puncture to assess cerebral spinal fluid (CSF) opening pressure. Neuroimaging was available to rule out cerebral venous thrombosis. Black patients were then compared with nonblack patients.

Anemia Common

The investigators found visual acuity, visual field loss, and degree of papilledema at presentation and follow-up was worse in black patients.

The relative risk of severe visual loss for black patients vs nonblack patients was 3.5 in at least 1 eye and 4.8 in both eyes.

The investigators also found obesity, systemic hypertension, anemia, and sleep apnea were more common in black patients than their nonblack counterparts.

Multivariate analyses also revealed race, anemia, BMI, and male sex were independent risk factors for severe visual loss and suggested racial differences may be partially accounted for by differences in CSF opening pressure, BMI, and frequency of anemia.

"We need to try to understand this racial difference a little more. But perhaps just as important is gaining a better understanding of some of the other possible risk factors that emerged," said Dr. Bruce.

For instance, the fact that IIH patients are more likely to have anemia could turn out to be an important part of treatment.

Team Effort Required

Currently, first-line treatment consists of lumbar puncture, which in can alleviate symptoms, and medical therapy with the diuretic acetazolimide and careful monitoring of the patient's visual field.

"IIH is not a condition neurologists can manage alone. They need to team up with an ophthalmologist, because this disease generally causes insidious peripheral vision loss that requires careful assessment and monitoring. In addition, papilledema is the number-one cause of vision loss, so this also needs frequent monitoring by an ophthalmologist," said Dr. Bruce.

IIH patients who are overweight or obese, said Dr. Bruce, are also advised to lose weight and are frequently referred to a dietitian to help support these efforts. In some cases, he said, bariatric surgery is also recommended.

Because IIH is a rare condition, attaining research funds has been a challenge. For now, investigators intend to continue to mine the current data set to try to gain more insight into the racial differences as well as other potential etiological factors. But ultimately, said Dr. Bruce, funding for a prospective clinical trial is needed.

The study was supported by Research to Prevent Blindness and the National Institutes of Health.

Neurology. 2008;70:861-867. Abstract

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