Idiopathic Intracranial Hypertension (IIH) Workup

Updated: May 17, 2017
  • Author: Mark S Gans, MD; Chief Editor: Andrew G Lee, MD  more...
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Workup

Approach Considerations

Idiopathic intracranial hypertension (IIH) should be suspected in patients with IIH risk factors who present with papilledema and headache. The cause of IIH is unknown; thus, it is a diagnosis of exclusion. Prior to diagnosis of IIH, structural causes of increased ICP need to be excluded with neuroimaging studies, and lumbar puncture should be performed to evaluate the CSF for other etiologies of elevated pressures. A thorough baseline ophthalmologic evaluation is also necessary to determine severity and to monitor disease progression.

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Laboratory Studies

Blood tests

Blood tests are useful for ruling out systemic lupus erythematosus or other collagen-vascular diseases, which have been reported as underlying conditions in some patients who present with (IIH). [58]

An increased incidence of anticardiolipin antibodies has been reported in patients with IIH. Accordingly, some authors advocate anticardiolipin antibody assessment in all IIH patients, regardless of prior history of thrombosis. [59] Some authors advocate screening for anticardiolipin antibodies and other procoagulant states in all patients with IIH who are either male or nonobese. [60]

Cases of IIH associated with Lyme disease have been reported. [61] Lyme disease screening (via enzyme-linked immunosorbent assay [ELISA]) should be considered in patients with a history of exposure to Lyme disease in endemic areas.

Most patients with typical history, gender, and body habitus need only routine blood work, including a complete blood cell (CBC) count to evaluate for anemia. [62]

Other studies that are unnecessary for routine evaluation but may be considered based on the patient’s presentation and risk factors include erythrocyte sedimentation rate (ESR), serum iron and iron-binding capacity, and antinuclear antigen (ANA) profile. In patients with a previous history of thrombosis or MRI evidence of dural venous sinus occlusion, additional procoagulant studies to consider include protein S, protein C, homocysteine levels, antithrombin III, factor V Leiden variant, antiphospholipid/anticardiolipin antibodies, lupus anticoagulant, and platelet aggregation studies.

CSF tests

CSF studies include the following:

  • Opening pressure
  • White blood cell (WBC) and differential counts
  • Red blood cell (RBC) count
  • Total protein
  • Quantitative protein electrophoresis
  • Glucose
  • Aerobic bacterial culture and sensitivity
  • Acid-fast bacilli (AFB) culture
  • Cryptococcal antigen (especially in patients with HIV)
  • Syphilis markers (eg, rapid plasma reagin [RPR])
  • Tumor markers and cytology (in patients with a history of cancer or with clinical features suggesting occult malignancy)

Most patients with typical history, gender, and body habitus need only routine CSF tests. However, extra fluid should be frozen in case the preliminary workup reveals unexpected abnormalities such as pleocytosis or elevated gamma globulin, which would indicate that more complete investigation for autoimmune, infectious, or neoplastic conditions is warranted.

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MRI and CT

A patient with bilateral disc swelling should undergo urgent neuroimaging studies to rule out an intracranial mass or a dural sinus thrombosis. In the setting of IIH, the findings on neuroimaging studies include normal or small slitlike ventricles, enlarged optic nerve sheaths, and, occasionally, an empty sella.

MRI of the brain with gadolinium enhancement is probably the study of choice for all patients with IIH, in that it provides sensitive screening for hydrocephalus, intracerebral masses, meningeal infiltrative or inflammatory disease, and dural venous sinus thrombosis. In a retrospective study of imaging features that have been suggested as typical for patients with IIH, only flattening of the posterior globe was found to be a reliable indicator of IIH, with a specificity of 100% and a sensitivity of 43.5%. [63]

MR venography can be useful for patients who are at greater risk for dural venous sinus thrombosis, such as those with suspected thrombosis on MRI, nonobese or male individuals, or those with a documented procoagulant state. Sagittal T1-weighted images often provide excellent views of the superior sagittal sinus, and these typically are included in routine MRI. Extraluminal narrowing of the transverse sinuses may be a typical feature of IIH, as reported by Farb et al. [8]

Computed tomography (CT) of the brain is less expensive than MRI and is adequate to rule out an intracranial lesion in most instances; however, MRI and magnetic resonance (MR) venography are more effective in ruling out a mass lesion and a dural sinus thrombosis, respectively. Although MR venography was once considered an elective imaging study for atypical patients, it is now increasingly accepted as a routine study for all patients with IIH. [64]

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Ultrasonography

Bedside ultrasonography has been used to identify intracranial hypertension by precisely measuring the diameter of the optic nerve sheath. [65] If this diameter increases in primary gaze and diminishes by 25% in eccentric gaze (30° test), then increased subarachnoid fluid surrounding the optic nerve is presumably present. This finding is consistent with papilledema if it is bilateral.

The drawback of this noninvasive technique is that it requires a highly skilled clinician to obtain reproducible results.

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Lumbar Puncture

Once an intracranial mass lesion is ruled out, lumbar puncture is indicated. The opening pressure should be measured with the patient relaxed in the decubitus position to prevent a falsely elevated pressure reading. If any specific difficulty was encountered that may have caused such as false elevation, the clinician performing the procedure must communicate this to the ophthalmologist. Unfortunately, some patients demonstrate a transiently normal pressure despite harboring IIH; confirming the disease in these patients is difficult.

Besides the value of the opening pressure, the clarity and the color of the cerebrospinal fluid should be noted. In addition, the cerebrospinal fluid (CSF) should be forwarded for cell count, cytology, culture, and measurement of glucose, protein, and electrolyte concentrations. All of these findings are normal in patients with IIH.

In obese patients, finding landmarks may be difficult; consequently, the tap is often performed with the patient seated. It should be kept in mind that the normal CSF pressure at the foramen magnum in the seated position is nearly 500 mm water from the lumbar entry point in persons of average height. Thus, an opening pressure of 500 mm water is extremely high for the lateral decubitus position but normal for the sitting position. If possible, the patient should be moved to the lateral decubitus position before the pressure is measured.

Another approach to lumbar puncture in obese patients utilizes fluoroscopic guidance in the radiology department. The prone positioning on the x-ray table and the increased abdominal pressure in this position may elevate the CSF pressure falsely. If the pressure is normal with the patient in the prone position, then the measurement is probably accurate. However, if it is high, the patient must be rolled into the lateral decubitus position and allowed to relax before a reliable pressure reading can be completed.

Obviously, such maneuvers carry a risk of displacing the needle from the thecal space. However, no alternative method exists for obtaining an accurate pressure reading.

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