What are the expected lumbar puncture (LP) findings in idiopathic intracranial hypertension (IIH)?

From the Guidelines

In idiopathic intracranial hypertension (IIH), the key lumbar puncture finding is elevated opening pressure, typically greater than 250 mm H2O in adults or 280 mm H2O in children, measured in the lateral decubitus position. Despite this high pressure, the cerebrospinal fluid (CSF) composition remains normal, with normal protein levels, normal glucose concentration, normal cell counts, and no evidence of infection or inflammation, as indicated by the consensus guidelines on management of IIH 1. The clear, colorless appearance of the CSF is preserved. These findings reflect the fundamental pathophysiology of IIH, which involves increased intracranial pressure without an identifiable structural cause such as a mass lesion, hydrocephalus, or meningeal inflammation. The normal CSF composition helps distinguish IIH from other conditions that can cause increased intracranial pressure, such as meningitis or subarachnoid hemorrhage.

Some key points to consider when interpreting lumbar puncture findings in IIH include:

• The measurement of opening pressure in the lateral decubitus position is crucial for accurate diagnosis 1.
• The CSF composition is expected to be normal, which is a key distinguishing feature from other causes of increased intracranial pressure.
• Serial lumbar punctures are not recommended for management of IIH due to limited relief and potential complications such as anxiety and back pain 1.
• The relief from a lumbar puncture is typically short-lived, as CSF is rapidly replaced 1.

Overall, the expected lumbar puncture findings in IIH are characterized by elevated opening pressure with normal CSF composition, which is essential for diagnosis and differentiation from other conditions.

From the Research

Expected LP Findings in Idiopathic Intracranial Hypertension

The expected lumbar puncture (LP) findings in idiopathic intracranial hypertension (IIH) include:

• Elevated cerebrospinal fluid (CSF) pressure, with a mean pressure of 37.7 cm H2O and a range of 29.5-66 cm H2O 2
• A CSF opening pressure of ≥ 250 mmH2O, which is a key diagnostic criterion for IIH 3
• Normal CSF composition, as IIH is characterized by elevated intracranial pressure without any abnormality in the CSF itself

Factors Associated with Elevated CSF Pressure in IIH

Several factors are associated with elevated CSF pressure in IIH, including:

• Frisén grade 2 or higher papilledema 3
• Tinnitus 3
• Empty sella 3
• Perioptic subarachnoid space distension 3
• Obesity 3

Therapeutic Effect of LP in IIH

LP may have a therapeutic effect in IIH, with studies showing:

• A significant reduction in papilledema grade after LP 4
• A decrease in peripapillary retinal nerve fibre layer thickness after LP 4
• An improvement in visual outcomes after LP, particularly in patients with mild vision loss and papilledema 5

Diagnostic Criteria for IIH

The diagnostic criteria for IIH include:

• Elevated CSF pressure, with a CSF opening pressure of ≥ 250 mmH2O 3
• Normal CSF composition
• Presence of papilledema
• Absence of any other cause of elevated intracranial pressure
• Presence of at least one of the following symptoms: headache, pulsatile tinnitus, transient visual obscurations, or diplopia 5