47 Idiopathic intracranial hypertension

Background

Definition

Idiopathic intracranial hypertension (IIH, also known as benign intracranial hypertension or pseudotumour cerebri) is defined as the presence of raised intracranial pressure without obvious abnormality on CT or MRI imaging of the head (in particular, no space-occupying lesion or enlargement of the ventricles), with no abnormality on examination of the cerebrospinal fluid constituents.1 It represents a significant cause of visual loss of varying degrees, including complete blindness.

Epidemiology

There have been few epidemiological studies of IIH,2–4 but these give fairly consistent figures for the incidence of the disease as 1–3 per 100 000 per year in those countries where it has been studied. IIH is much more common in women,2–5 particularly obese women, when the incidence is as high as 21 per 100,000 per year.4 It also occurs in children, in whom it is not more common in females6 and in whom the incidence is reported to be 0·4–2·2 per 100 000 per year.7

Presentation

IIH usually presents with headaches and/or visual disturbance. The majority of patients have bilateral papilloedema, but there are reports of patients with unilateral papilloedema8 and of patients without papilloedema.9,10 A number of other physical signs may occur occasionally, but the only other physical sign that typically occurs is sixth nerve palsy. Though headache is a major source of morbidity,11 the only major complication of the condition is visual loss. Blindness has been reported to occur in 10% of cases,12 but varying degrees of visual loss occur in up to 87% if patients are carefully monitored.13 The major aim of therapy is thus to prevent visual loss, but other management issues include treatment of headache, and treatment of visual loss once it has occurred.

Aetiology

The cause of IIH remains unknown. Various theories have been proposed relating to the possibility of increased brain, blood or cerebrospinal fluid (CSF) volumes, or the possiblity of increased secretion of CSF. However, the most generally accepted theory is that there is some form of resistance to

CSF outflow, possibly at the level of the arachnoid villi. Support for this theory derives from the fact that cortical venous sinus thrombosis (CVST) gives rise to a similar clinical picture (and for many years has been confused with IIH). Modern imaging techniques are now able to detect venous sinus thrombosis relatively easily, and such patients are now not included in the definition of IIH. Accordingly, CVST is not discussed further in this chapter, and the reader is referred to other work for further information.14

Risk factors

There have been countless reports in the literature of a potential association between IIH and many different medical conditions or treatments, most notably obesity, vitamin A or its analogues (for example, isoretinoin), tetracyclines, renal disease and the oral contraceptive pill.15,16 Only two major case-control studies have been performed,11,17 and these have only shown a statistically significant relationship between IIH and female sex, being of reproductive age, obesity and recent weight gain. However, it should be borne in mind that the numbers involved in these studies were relatively small, and so other possible significant associations cannot be excluded.

Prognosis

The prognosis is variable. In some patients, the disease is relatively self-limiting, but it can continue for many years. It is also possible that patients may relapse following previous resolution of symptoms and signs.

Treatment options

Various different forms of management have been suggested in the literature. These include:

●weight loss either by dieting or aided by gastric (bariatric) surgery18,19

●repeated lumbar puncture20

●continuous negative abdominal pressure21

●pharmacological treatment with diuretics, for example, (most notably acetazolamide), glycerol or corticosteroids22

●surgical treament, usually optic nerve sheath fenestration (ONSF)23–26 or lumboperitoneal shunting (LPS)27

●other techniques such as subtemporal decompression,20 cisternoperitoneal or ventriculoperitoneal shunts.

There are many non-systematic reviews of IIH in the literature,6,15,16,28–33 and a Cochrane systematic review.34 Details of the various treatments can be obtained from nonsystematic reviews elsewhere.15,16,33

Question

What is the best way to manage IIH in order to prevent visual loss?

The evidence

All management techniques have their proponents (and, in some cases, strong opponents).35 However, a systematic review34 has found that none of these procedures has yet been subjected to a controlled trial, let alone a randomised controlled trial.

Question

What is the best way to manage the headache that occurs in IIH?

The evidence

None of these treatments has been subjected to RCTs in the context of IIH.

Comment

The various treatments listed have all been reported to reduce headache in some, but not all patients (including, interestingly, ONSF).23–25 It is often possible to treat the headache with standard headache therapies such as physiotherapy, non-steroidal anti-inflammatory drugs, antimigraine therapy or tricyclic antidepressants.

Question

What is the best treatment for a patient with IIH who has evidence of visual loss?

The evidence

As above, possible management options for dealing with acute or subacute visual loss include lumbar puncture, surgical procedures, usually ONSF or LPS, but ventriculoperitoneal shunting has also been advocated. Again, no relevant RCTs exist.

Discussion

IIH is a significant cause of visual loss. Because of its numerous symptoms, it is possible for patients to present to various different specialities, including ophthalmology, neurology, neurosurgery, ENT or general medicine. Each discipline is likely to have their own preferred treatment option(s), and the management of individual patients is therefore largely dependent upon which medical speciality they were first referred to, for example, LPS is often easier if patients are being seen by neurosurgeons, ONSF if they are being seen by ophthalmologists. The condition is not rare: because it may go on for many years, the prevalence is considerably higher than the incidence, and patients need to be seen regularly for follow up to make sure they are not losing vision. Consequently, patients with IIH consume a large amount of healthcare resource that might be reduced if only the answers to the above questions were known.

Implications for practice

For the moment, management of patients with IIH has to be done without adequate evidence for or against the various treatment options. In the circumstances, it would seem reasonable to continue to do whatever is felt to be safe and effective until more formal evidence is available. In the absence of adequate information, a guide to “how we do it” has been published elsewhere.36

Implications for research

It is clear that there is a desperate need for RCTs in the management of this condition. In particular, there is a need to compare the two major invasive procedures of

lumboperitoneal shunting and optic nerve sheath fenestration in a head-to-head trial. In addition, randomised controlled studies of the more non-invasive treatments including diuretics, weight loss and lumbar puncture are needed to work out which of these treatments is most appropriate and in what situation(s) they should be used.

References

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