What is Idiopathic Intracranial Hypertension?
Idiopathic intracranial hypertension is a neurological condition characterized by increase in intracranial pressure likely due to obstruction in venous drainage without the evidence of a mass, lesion or hydrocephalus. Idiopathic intracranial hypertension usually occurs in women within the child bearing age predominantly in obese women. In patients affected by Idiopathic intracranial hypertension, the cerebrospinal fluid composition is usually normal; however, the intracranial pressure is above normal limits (> 250 mm H2O). This condition can also develop in children after discontinuing corticosteroid or after taking large dosage of tetracycline.
Idiopathic intracranial hypertension is known by other synonyms such as pseudotumor cerebri and benign intracranial hypertension.
Causes of Idiopathic Intracranial Hypertension
The exact cause of this condition is unknown; however, the most accepted cause of idiopathic intracranial hypertension is obstruction in the cerebral venous outflow, which is possibly because of the venous sinuses being smaller in size than normal.
Symptoms of Idiopathic Intracranial Hypertension
The most common symptoms of Idiopathic intracranial hypertension include increased intracranial pressure and optic disc swelling or papilledema. Papilledema may develop bilaterally or unilaterally, which may or may not be symptomatic initially and is usually detected during regular eye examination. Other symptoms of Idiopathic intracranial hypertension include:
- Frequent headache with fluctuating intensity.
- Diplopia secondary to 6th cranial nerve dysfunction. This is usually horizontal and rarely vertical.
- Pulsatile intracranial tinnitus.
- Neurological examination may reveal evidence of 6th cranial nerve palsy, which is otherwise unremarkable.
- Radicular pain predominantly in the arms.
Visual symptoms of papilledema include:
- Transient obscuration of vision.
- Visual loss that begins peripherally in one or both eyes and may lead to permanent loss of vision if left untreated.
- Nerve fiber layer defects.
- Enlargement of the blind spot.
- Metamorphopsia i.e. blurring and distortion of central vision secondary to optic neuropathy or macular edema
- Sudden loss of vision secondary to associated anterior ischemic optic neuropathy.
Nonspecific symptoms of idiopathic intracranial hypertension include dizziness, photopsias, vomiting or retrobulbar pain.
Epidemiology of Idiopathic Intracranial Hypertension
Idiopathic intracranial hypertension is more common among females than in males. Incidence of idiopathic intracranial hypertension in normal weight women is about 1/100,000 and in obese women it is about 20/100,000. This condition usually affects in the third decade of life. Rarely, idiopathic intracranial hypertension affects the pediatric patients who are not overweight. At present, there are no evidence suggesting predilection of this disease in a particular race or ethnic group. Idiopathic intracranial hypertension is not associated with specific mortality. Morbidity rate is predominantly associated with effects of papilledema on visual issues.
Pathophysiology of Idiopathic Intracranial Hypertension
The exact pathophysiology of idiopathic intracranial hypertension is yet unknown. A large number of studies are being carried to get a better understanding of the condition. The older theories state that increase in intracranial pressure is possibly due to cerebral edema. The newer theories state that there may be a link between obstructive segments in the distal transverse sinus and idiopathic intracranial hypertension with presence of arterial inflow accompanied by low grade stenosis of transverse sinus.
Risk Factors of Idiopathic Intracranial Hypertension
The most common risks factors include:
- Child bearing age in women.
- Obesity and increased body mass indexes (BMIs).
- Recent history of exposure to specific exogenous substances and certain drugs such as amiodarone, carbidopa, levodopa, chlordecone, growth hormones, oral contraceptives, oxytocin, phenytoin, cyclosporine, indomethacin, lead, leuprolide, antibiotics such as penicillin, tetracycline, nalidixic acid etc.
- Presence of systemic disease such as Lyme disease, anemia, chronic respiratory disease, familial mediterranean fever, hypertension, multiple sclerosis, polyangiitis overlap syndrome, chronic renal disease, Reye syndrome etc.
- Obstruction in cerebral venous flow.
- Presence of endocrine and metabolic disorders such as adrenal insufficiency, Cushing disease, hypothyroidism, hypoparathyroidism etc.
Diagnosis of Idiopathic Intracranial Hypertension
Diagnostic criteria for idiopathic intracranial hypertension were described by Dandy in 1937, which was redefined by Smith in 1985. These criteria are as follows:
- Presence of signs and symptoms of elevated intracranial pressure
- Absence of localizing neurological signs with exception of 6th nerve paresis.
- Increased cerebrospinal fluid (CSF) pressure without cytological or chemical abnormalities.
- Presence of normal to moderate symmetric ventricles.
Diagnosis of idiopathic intracranial hypertension is done with the help of investigative studies such as complete blood count, tests for estimating electrolyte and bicarbonate levels, full pro-coagulant profile. Neuro imaging studies are done to rule out possibility of intracranial lesion and dural sinus thrombosis. MRI/MRV of the brain with gadolinium and lumbar puncture are helpful in correct diagnosis of idiopathic intracranial hypertension. CT scan of brain may be considered if MRI is not available immediately. Lumbar puncture is carried out with the patient in lateral decubitus position. Cerebrospinal fluid (CSF) studies may include the following tests:
- White blood cell and differential counts.
- Red blood cell count.
- Total protein level.
- Opening pressure.
- Glucose level.
- Aerobic bacterial culture and sensitivity.
- Quantitative protein electrophoresis.
- Acid-fast bacilli culture.
- Cryptococcal antigen (predominantly in patients with HIV).
- Tumor markers and cytology (in patients suspected to have cancer or malignancies).
- Syphilis markers (eg. Rapid plasma re-gain [RPR]).
Visual function tests are one of the most important tests and include the following:
- Optic nerve photography, ophthalmoscopy and optical coherence tomography (OCT).
- Formal visual field assessment.
- Ocular motility examination.
Treatment of Idiopathic Intracranial Hypertension
Pharmacologic therapy for idiopathic intracranial hypertension includes treatment with:
- Acetazolamide (beneficial in lowering intracranial pressure) or furosemide.
- Amitriptyline, propranolol, topiramate are usually prescribed for management of headache.
- In certain cases corticosteroids may be prescribed for lowering intracranial pressure. Steroid should be used on a short-term basis plan and should only be used in patients with marked loss of visual function.
In advanced cases of idiopathic intracranial hypertension, surgical intervention is considered. These include:
- Optic Nerve Sheath Fenestration. It is a procedure done to decompress the fluid around the optic nerve.
- Cerebrospinal fluid diversion done by lumboperitoneal shunt or ventriculoperitoneal shunt.
- Intracranial venous sinus stenting.
- Serial lumbar puncture may be considered in rare cases such as in pregnant patients where conventional treatment cannot be done.
Weight loss is strongly recommended in patients affected by idiopathic intracranial hypertension. It is advised to exercise on a regular basis, follow a healthy diet and a healthy lifestyle. Bariatric surgery provides significant benefit.
Prognosis of Idiopathic Intracranial Hypertension
Symptoms of idiopathic intracranial hypertension may last from a few months to several years. In most of the cases, the symptoms worsen gradually. Treatment provides gradual improvement in symptoms and stabilization in symptoms after a period of time; however, it does not provide complete recovery at all times. A large number of patients has persistent papilledema and increased intracranial pressure.
Complications of Idiopathic Intracranial Hypertension
Complications of idiopathic intracranial hypertension are mainly associated with effects of papilledema on vision. Longstanding papilledema if left untreated, can lead to serious complications such as optic neuropathy with constriction of the visual field and color blindness. In most of the cases, the central visual acuity may be noted in end-stage papilledema.
Idiopathic intracranial hypertension is a condition that mainly affects obese women in child-bearing age. The key features of this condition are increased intracranial pressure and papilledema. The exact etiology of idiopathic intracranial hypertension is unknown. It is also known by the name pseudotumor cerebri and benign intracranial hypertension. The exact etiology and causes of idiopathic intracranial hypertension is unclear at present. The most accepted cause of idiopathic intracranial hypertension is obstruction in the cerebral venous outflow. Women who are obese and in the child bearing age must take special precaution to lose weight to avoid the condition and those who are pregnant must get their regular checkups done without fail to avoid it.