Idiopathic intracranial hypertension

Synonyms: pseudotumour cerebri, benign intracranial hypertension

What is idiopathic intracranial hypertension (IIH)?

Raised intracranial pressure in the absence of a mass lesion or of hydrocephalus. It is often idiopathic. Idiopathic intracranial hypertension (IIH) appears to be due to impaired cerebrospinal fluid (CSF) absorption from the subarachnoid space across the arachnoid villi into the dural sinuses.

Idiopathic intracranial hypertension can lead to significant visual impairment, so prompt recognition and treatment are needed to prevent potentially permanent visual changes including partial or total loss of vision.

Epidemiology

• Idiopathic intracranial hypertension most frequently occurs in obese women of childbearing age.

• Its prevalence ranges between 0.5 and 2 per 100,000 of the general population and is expected to increase further as obesity increases worldwide¹ .

• The incidence in the UK general population is approximately 4.7 per 100,000 and this has recently increased in parallel with obesity² .

Risk factors

• Being overweight (90% patients).

• There is an increased risk in women with menstrual irregularity.

• Female-to-male ratio is between 3:1 to 8:1.

• In women it may coincide with recent weight gain, fluid retention, the first trimester of pregnancy and the postpartum period.

• It is increasingly prevalent in deprived populations³ .

Aetiology

The underlying cause of the disease remains unknown. Several mechanisms have been proposed as the underlying cause of IIH:

• An overproduction of cerebrospinal fluid (CSF).

• Outflow obstruction.

• Elevated pressure in the venous sinuses.

• Dysfunction in the glymphatic pathway.

• Hormonal alterations.

None adequately explains the whole clinical picture. Increasing evidence suggests that a CSF overproduction is unlikely to be the cause of IIH¹ .

Associations

Known associations include:

• Endocrine: adrenal insufficiency, Cushing's syndrome, hypoparathyroidism, hypothyroidism and hyperthyroidism.

• Medication: cimetidine, corticosteroids, danazol, isotretinoin, levothyroxine, lithium, minocycline, nalidixic acid, nitrofurantoin, tamoxifen, tetracycline, ciclosporin, levonorgestrel implant, pancreatin, recombinant and natural human growth hormone, vitamin A in infants.

• Miscellaneous: polycythaemia vera, iron-deficiency anaemia, chronic kidney disease, systemic lupus erythematosus, Lyme disease.

Idiopathic intracranial hypertension symptoms

• Headache tends to be the first symptom: generalised throbbing is worst first thing in the morning and last thing at night. It is relieved on standing (consistent with raised intracranial pressure). It is also aggravated by straining, coughing or a change in position. In many cases, the headache may be mild, nonspecific and have been present for many weeks or months.

• Gradual visual field defects; moderate or gross bilateral papilloedema without significant focal intracranial signs. Identification of papilloedema is a common source of error in the diagnosis, as it is both under- and over-diagnosed² .

• Daily transient visual obscurations (TVOs) ('greying out') on bending or stooping, halo or a short episode of visual Catherine wheel flashes, persistent blurring, scotoma or horizontal diplopia often occur.

• Nausea, vomiting, drowsiness.

• Diplopia (due to VI cranial nerve palsy, cognitive deficits, tinnitus and olfactory dysfunction are less common¹ .

Differential diagnosis

• Other causes of headache, including cerebral tumours and malignant hypertension.

• Other causes of papilloedema.

• Other causes of visual disturbance.

Investigations⁴

These are primarily to exclude any other possible cause of raised intracranial pressure.

• Recommended blood tests include: FBC, ESR, iron studies, antinuclear antibodies, coagulation studies⁵ .

• Screening for Lyme disease is recommended in patients who have a history of exposure to Lyme disease in areas of endemic disease⁶ .

• CT or MRI scanning: the ventricles, in contrast to hydrocephalus, are normal or reduced in size.

• Visual field charting: enlarged blind spot and peripheral field construction.

• Lumbar puncture, if not contra-indicated by clinical features and pressure measurement. Monitor intracranial pressure if in doubt as to the diagnosis. Lumbar puncture reveals pressure greater than 250 mm CSF with normal constituents² .

Idiopathic intracranial hypertension treatment and management^{1 4}

The main principles of treatment are:

a) Treatment of the underlying disease.

b) Protection of the vision; and

c) Minimising morbidity caused by headache.

Treatment of the underlying disease

• Weight reduction is the mainstay of this principle.. Patients with a BMI >30 kg/m² should be sensitively counselled about weight management.

• Amount of weight loss required is not known, but up to 15% weight was required to put IIH into remission in one cohort⁷ .

• Acetazolamide appears to be the most effective agent for lowering intracranial pressure although the 2015 Cochrane review shows only modest benefit for its use^{8 9} .

• Topiramate is becoming popular as a therapeutic option because it treats migraine, suppresses the appetite and inhibits carbonic anhydrase.

Protection of the vision

• Use of acetazolamide or topiramate reduces pressure on the optic nerve.

Headache morbidity

• Headaches are usually migrainous.

• Migraine preventers (that do not increase appetite) are appropriate.

• Overuse of acute analgesic medication should be assessed, as this is a common observation in IIH patients.

Surgery

Surgical intervention may be considered if other measures are ineffective or there is a rapid or progressive decline in visual function. Surgical options include¹⁰ :

• Optic nerve sheath fenestration (decompression).

• CSF shunting (lumbo-peritoneal,ventriculo-peritoneal shunt, ventriculojugular and vetriculoatrial shunts).

• Intracranial venous sinus stenting

The treatment offered often depends on the local expertise available and should always occur in conjunction with weight loss.

Prognosis¹¹

• Idiopathic intracranial hypertension is not known to be associated with any specific effect on mortality.

• In a retrospective analysis the prognosis was good in 64.7% of the patients and 35.3% of the patients clinically worsened.

• Recurrence of symptoms was observed in 33% of the patients and four patients had severe permanent vision loss.

• Demographic features, initial complaints, mean ICP, and pathological magnetic resonance imaging findings were not associated with the prognosis.

• Delay in treatment and generalised constriction in the visual field were associated with the poor prognosis.