Idiopathic Intracranial Hypertension

Question 1

… is a disorder characterised by features of raised intracranial pressure.

Answer 1

Idiopathic intracranial hypertension is a disorder characterised by features of raised intracranial pressure.

Question 2

Idiopathic intracranial hypertension (IIH) is a disorder caused by…

Answer 2

Idiopathic intracranial hypertension (IIH) is a disorder caused by chronically elevated intracranial pressure (ICP), which leads to the characteristic clinical features of headache, papilloedema (swollen optic discs) and visual loss. The actual cause of the condition remains unknown, but it primarily affects overweight women of childbearing age.

Question 3

Epidemiology

IIH

Answer 3

The annual incidence of IIH is approximately 1-2 per 100,000 population.

Question 4

The highest incidence of IIH is seen in women of childbearing age. In this group the incidence is as high as 21 per 100,000. The condition is strongly linked with …

Interestingly, although the incidence is much lower in men, they are at increased risk of visual loss.

Answer 4

The highest incidence of IIH is seen in women of childbearing age. In this group the incidence is as high as 21 per 100,000. The condition is strongly linked with obesity, and due to the rising obesity epidemic, rates are increasing. There is no major difference observed between ethnic groups.

Interestingly, although the incidence is much lower in men, they are at increased risk of visual loss.

Question 5

IIH aetiology

Answer 5

IIH is idiopathic, meaning we do not know the underlying cause. However, weight and sex remain the most prominent risk factors for development of the condition.

Question 6

RF for IIH

Answer 6

Weight: increased incidence in overweight and obese patients. Recent weight gain and higher body mass index is associated with higher risk of IIH
Sex: much greater incidence in females
Age: reproductive age

Question 7

Associated conditions - IIH

Answer 7

IIH has been associated with several conditions and medications, although this only represents a small proportion of patients. In the literature there are many reported associations, but the evidence for many of these is limited.

The underlying association with some conditions may be related to a specific mechanism. For example, in hypercoagulable conditions there may be obstruction to venous outflow due to occult venous sinus thrombosis. Associations can be broadly divided into medication use, diet and systemic illnesses.

Medication use: Growth hormone, tetracyclines, retinoids
Dietary: excess vitamin A intake
Systemic illnesses: sleep apnoea, hypercoagulable disorders, polycystic ovarian syndrome, systemic lupus erythematosus, Behçet syndrome, endocrinopathies (e.g. Addison’s, hypoparathyroidism).

Question 8

The clinical manifestations of IIH occur due to raised ICP. The mechanisms leading to raised ICP is unknown, but several theories exist, which include: (4)

Answer 8

Intracranial venous hypertension: due to venous sinus narrowing/stenosis (may be a consequence of raised ICP rather than the direct cause). Thought to occur in distal transverse sinus segments
Raised intra-abdominal pressure from central obesity: felt to increase central venous pressure and subsequently leads to an increase in ICP
Altered sodium and water retention
Impaired CSF reabsorption: occurring secondary to excess vitamin A or formation of micothrombi in the cerebral venous circulation

Question 9

IIH is characterised by clinical features of raised intracranial pressure.

Answer 9

Any cause of raised ICP can lead to the characteristic features of headache (worse on lying down or bending over), papilloedema, and visual changes. Headache is the most common presenting feature in IIH.

IIH should be highly suspected in women of childbearing age who present with headache and papilloedema.

Question 10

Symptoms of IIH

Answer 10

Headache: worse on lying down or bending over. Often worse in the morning.
Transient visual loss: usually last seconds, may be precipitated by position change. Unilateral or bilateral.
Photopsia: refers to flashes of light.
Tinnitus (pulsatile): refers to a ringing/buzzing noise in the ear
Diplopia (double vision): typically on horizontal gaze. Most often due to unilateral or bilateral sixth cranial nerve (abducens) palsy. This is because of the long intracranial course of the sixth nerve, which is at risk of compression at the skull base with raised ICP.
Visual loss (most concerning complication)
Other features: neck, back and/or retrobulbar pain (i.e. pain behind the eyes).

Question 11

IIH should be highly suspected in women of childbearing age who present with headache and ….

Answer 11

IIH should be highly suspected in women of childbearing age who present with headache and papilloedema.

Question 12

IIH should be highly suspected in women of childbearing age who present with .. and papilloedema.

Answer 12

IIH should be highly suspected in women of childbearing age who present with headache and papilloedema.

Question 13

Signs (IIH)

Answer 13

Papilloedema: refers to a swollen optic disc secondary to raised ICP. May be graded 0-5. Features include blurring of the disc margins, adjacent haemorrhage, swollen disc with oedema and obscuration of major vessels over the optic disc
Visual loss: formal visual field testing is essential. Common patterns include enlarged blind spot, partial arcuate defect (small bow-shaped visual field defect, not crossing the midline), and peripheral field loss
Sixth nerve palsy: causes a lateral rectus palsy with failed eye abduction on horizontal gaze

Question 14

What does this show?

Answer 14

Retinal image showing papilloedema (Think IIH)

Question 15

Before making a diagnosis of IIH, it is important to exclude structural causes of raised ICP with ….

Answer 15

Before making a diagnosis of IIH, it is important to exclude structural causes of raised ICP with neuroimaging.

Question 16

The diagnosis of IIH is usually made by clinical features of raised ICP, identification of raised pressures on lumbar puncture and exclusion of an alternative cause using neuroimaging (e.g. space-occupying lesion, hydrocephalus, venous sinus thrombosis).

A formal diagnostic criteria is often used known as the modified Dandy criteria. This criteria has several components:

Answer 16

Typical symptoms
Absence of additional neurological features
Raised ICP with normal cerebrospinal fluid composition
Absence of another cause of intracranial hypertension

Question 17

Any condition causing raised ICP can lead to headache and papilloedema. Most of these conditions can be excluded using magnetic resonance imaging (MRI) including venography to exclude venous sinus thrombosis.

Answer 17

Space-occupying lesion: primary CNS malignancy, metastatic deposit, cerebral abscess
Venous outflow obstruction: venous sinus thrombosis
Obstructive hydrocephalus: blockage to CSF leaving the ventricular system
Decreased CSF reabsorption: subarachnoid haemorrhage, post-meningitis
Increased CSF production: choroid plexus papilloma

Question 18

Optic disc swelling may be unilateral or bilateral, of which there are numerous causes.
There are numerous causes of optic disc swelling that may be divided into different categories:

Answer 18

Intracranial conditions: cause optic disc swelling due to raised ICP. Known as papilloedema.
Optic nerve pathologies (e.g. optic neuritis)
Vascular conditions (e.g. retinal artery or vein occlusion)
Conditions affecting the globe (e.g. uveitis)

Question 19

Investigations are important to exclude an alternative cause for raised intracranial pressure.

Answer 19

Neuroimaging and lumbar puncture are the two critical investigations in the work-up of IIH. Most other causes of raised ICP can be excluded through neuroimaging.

Observations: BP is crucial in any patient presenting with headache
Urinalysis: needed to exclude pregnancy and look for renal disease
Bloods: basic laboratory tests (FBC, U&E, CRP, coagulation) are important to assess for clues of alternative diagnoses and to ensure it is safe to proceed with lumbar puncture.
Ophthalmoscopy: basic bedside assessment to exclude papilloedema. Should be followed by formal ophthalmic assessment (including visual fields) if IIH is diagnosed or highly suspected.

Imaging of the brain with MRI with a venography phase (MRV) is needed to exclude alternative causes of raised ICP. CT imaging may be used acutely (e.g. for acute presentations to exclude serious alternative diagnoses such as intracerebral haemorrhage), or when MRI is not possible (e.g. incompatible pacemaker, claustrophobia).

Question 20

Imaging of the brain with MRI with a.. …(MRV) is needed to exclude alternative causes of raised ICP.

Answer 20

Imaging of the brain with MRI with a venography phase (MRV) is needed to exclude alternative causes of raised ICP.

Question 21

Lumbar puncture - IIH

Answer 21

A lumbar puncture (LP) should be performed in all patients with suspected IIH if no contraindications. The diagnosis of IIH is based on measurement of the opening pressure (cmH20) taken in the lateral decubitus position (i.e. lying on your side). In IIH, the opening pressure is elevated. Basic CSF analysis should be completed in all samples including cell count, MC&S, protein and glucose. These are characteristically normal in IIH.

Question 22

LP pressures - IIH

Answer 22

Normal opening pressure (10-20 cmH20)
Mildly elevated (20-25 cmH20): may be diagnostic of IIH if other characteristic features are present (e.g. MRI findings)
Markedly elevated (>25 cmH20): consistent with IIH

Question 23

IIH LP pressure - why may it be falsely low?

Answer 23

Occasionally, the opening pressure may be falsely low due to other factors (e.g. Multiple attempts, hyperventilation, ICP-lowering medications). In addition, ICP pressure varies during the day. Therefore, if the opening pressure is low or mildly elevated and IIH is strongly suspected, a repeat LP should be considered.

Question 24

Management of IIH

Answer 24

Weight loss and use of carbonic anhydrase inhibitors (e.g. acetazolamide) form the cornerstone of treatment.

Question 25

Weight loss

IIH

Answer 25

Weight loss is the principle advice that is usually combined with medical therapy due to the time required to make significant improvements in weight. A low sodium weight loss programme should be advised. Severely obese patients may require weight reduction surgery to help achieve weight loss.

Question 26

Serial lumbar punctures - IIH

Answer 26

Occasionally, serial lumbar punctures may be offered to patients. This involves performing an LP to remove excess CSF to reduce ICP. This should not be offered as a sole treatment and typically used as a temporary measure in patients who are likely to undergo surgery or cannot tolerate medical therapy.

Question 27

The use of a carbonic anhydrase inhibitor (e.g. ;…) is the treatment of choice for IIH.

Answer 27

Acetazolamide 500 mg orally BD: titrated upward as needed

Question 28

The use of a carbonic anhydrase inhibitor (e.g. acetazolamide) is the treatment of choice for IIH.
What do they do?

Answer 28

Carbonic anhydrase inhibitors are thought to work by reducing the amount of CSF production. This leads to a lower CSF pressure, less papilloedema, and improved visual testing. The BNF advises avoiding acetazolamide in pregnancy (particularly in the first trimester). These patients may require serial lumbar punctures if acetazolamide is felt too unsafe to use.

Question 29

Other medications that may be used in IIH:

Answer 29

Topiramate: anti-epileptic drug with activity against carbonic anhydrase
Furosemide: loop diuretic that can be used as an adjunct to acetazolamide

Question 30

IIH

Several surgical and newer interventional radiological procedures (e.g. venous sinus stenting) may be offered to patients with ongoing symptoms despite medical therapy. Some indications for surgery include worsening visual function despite medical therapy and intractable headache.

Main options include:

Answer 30

Optic nerve sheath fenestration: small incisions are made to the optic nerve sheath to create a window that allows CSF to be released. This reduces pressure on the optic nerve head.
Shunting: involves placement of a surgical shunt between CSF (e.g. ventricular system or lumbar spine) and another body cavity (e.g. peritoneum). Typical shunts include ventriculo-peritoneal or Lumbar-peritoneal. This helps to shunt CSF and reduce ICP.

Question 31

The major long-term complication of IIH is …

Answer 31

The major long-term complication of IIH is permanent visual loss.

Question 32

Prognosis - IIH

Answer 32

In the majority of patients, symptoms slowly worsen over time. Treatment can help improve or stabilise symptoms, but complete recovery is not possible in all patients. Recurrence (the development of symptoms after recovery or worsening after a period of stability) can occur in over a third of patients.

Longterm, the major concern is permanent visual loss. A subset of patients seem to have a more fulminant course with rapid progression to visual loss.