Idiopathic intracranial hypertension

In the linked prospective cohort study (doi:10.1136/bmj.c2701), Sinclair and colleagues observed intracranial pressure in patients with idiopathic intracranial hypertension who follow a low energy diet.1 This condition is often chronic and is characterised by symptoms and signs of intracranial hypertension, with no cause found by adequate imaging studies, and normal cerebrospinal fluid.2 Visual loss from papilloedema is the most feared visual complication.2 Headaches (which are difficult to treat) and depression are common, and quality of life is often reduced.3 4

Medical treatment of idiopathic intracranial hypertension consists of acetazolamide and other diuretics, which are thought to reduce the formation of cerebrospinal fluid.5 Because most affected people are obese, weight loss has been suggested. When visual loss occurs, surgical cerebrospinal fluid drainage procedures such as lumbar or ventriculo-peritoneal shunting or optic nerve sheath fenestration are performed. A recent systematic review found no randomised or controlled trials of treatment of the condition and called for such evidence.6

The risk of this condition is at least eight times higher in overweight or obese people.7 In the 15-44 age group, the incidence increases from 3.5 per 100 000 in normal weight women to 13 per 100 000 in overweight women to almost 20 per 100 000 in obese women. Although the incidence is lower in normal weight men (0.3 per 100 000), obese men also have a higher incidence (1.5 per 100 000).8

Weight loss improves the symptoms and signs of the condition. Retrospective case series studies have reported that weight loss reduces papilloedema and improves vision.9 10 An uncontrolled study reported that bariatric surgery was associated with profound weight loss, resolution of papilloedema, and normalisation of intracranial pressure.11

The only previous prospective study was carried out in 1974, and a strict diet was associated with weight loss and reduced papilloedema.12 The study was uncontrolled and used no scans or lumbar punctures, and it did not grade papilloedema or visual outcome.

Sinclair and colleagues’ study is the first well designed prospective study of women with chronic idiopathic intracranial hypertension.1 It found that a strict diet produced weight loss and also reduced papilloedema grade, headache, and intracranial pressure. Each woman was used as her own control, with a three month period when she received her usual treatment—normally acetazolamide. In the first three months the patients’ baseline data were established. During the second three month period the women received a very low energy diet (1777 kJ/day; 425 kcal/day) that resulted in an average weight loss of 16 kg (or 15% of body weight). The final three months ascertained whether the women could maintain the progressmade in the previous three months. Each woman underwent intracranial pressure measurements, visual function testing (visual acuity, automated perimetry, colour testing, and contrast sensitivity), three tests to ascertain papilloedema grade (visual inspection of fundus photographs, optical coherence tomography, and optic nerve ultrasound), and a validated headache measure (HIT-5). Surprisingly, only two of the 25 subjects dropped out because of the restrictive diet. The authors found that visual acuity and contrast sensitivity significantly improved. Visual fields were stable. Papilloedema significantly improved as measured by ultrasound and optical coherence tomography but not by Frisén grade. Headaches, tinnitus, and diplopia significantly improved. Gains made in the treatment phase were maintained during the three month follow-up, except for headache.

Although almost all studies,10 11 12 including this one, have shown that weight loss is associated with reduced intracranial pressure, intracranial pressure does not always correlate with weight loss or symptoms. In the current study only four of 20 patients developed normal intracranial pressure (less than 250 mm cerebrospinal fluid) despite aggressive weight loss. Thirteen of the 16 women who continued to have increased intracranial pressure experienced improvement in many of their symptoms, including visual changes and tinnitus. This is not surprising, because idiopathic intracranial hypertension is probably a chronic disorder and lumbar punctures done years after the diagnosis have shown raised intracranial pressures.2

What are the implications of these results for practising clinicians? The uncontrolled and now prospectively controlled evidence suggests that weight loss may be an effective treatment for patients with idiopathic intracranial hypertension. Clinicians could recommend the replacement liquid diet used by Sinclair and colleagues, or another low energy diet, and stress to patients that weight loss may improve symptoms and signs.

This study does not clarify the role of diuretics, especially acetazolamide, because the authors allowed patients to continue taking their usual drugs, and almost half were on a steady dose of acetazolamide. A randomised placebo controlled trial is now under way in the United States to try to answer this question. It is also unknown whether weight loss would also improve quality of life and reduce depression.