In a 13‑year‑old girl with normal brain MRI except nonspecific bright foci, resolved nausea and vomiting, chronic fatigue, and transient sixth‑nerve palsy on waking, what is the most likely diagnosis and what urgent work‑up and initial treatment are recommended?

Idiopathic Intracranial Hypertension (IIH) Without Papilledema

This 13-year-old girl most likely has IIH without papilledema (IIHWOP), a rare subtype that requires urgent lumbar puncture to measure opening pressure and initiate treatment to prevent visual deterioration. 1

Why This Diagnosis Fits

The clinical picture strongly suggests IIH despite the absence of papilledema:

• Transient sixth nerve palsy on waking is a hallmark cranial nerve finding in IIH, and typically there should be no other cranial nerve involvement 1
• Resolved nausea and vomiting are consistent with elevated intracranial pressure symptoms that can fluctuate 1
• Chronic fatigue accompanies the syndrome 1
• Normal brain MRI except nonspecific bright foci excludes mass, hydrocephalus, structural lesions, and abnormal meningeal enhancement—all required for IIH diagnosis 1
• Nonspecific bright foci (white matter hyperintensities) are not pathognomonic but can be seen in IIH and do not exclude the diagnosis 1, 2

Urgent Work-Up Required

Immediate Neuroimaging (Within 24 Hours)

MR venography is mandatory to exclude cerebral venous sinus thrombosis, which can present identically and requires anticoagulation 1. CT or MR venography must be completed within 24 hours 1.

Lumbar Puncture (After Normal Venography)

Following normal venography, all patients with suspected IIH require lumbar puncture to measure opening pressure and confirm normal CSF composition 1:

• Technique: Perform in lateral decubitus position with legs extended for accurate measurement 1, 2
• Diagnostic threshold: Opening pressure ≥250 mm H₂O confirms IIH 1, 2
• CSF analysis: Must show normal cell count, protein, glucose, and no organisms to satisfy diagnostic criteria 1, 2

Ophthalmologic Evaluation

Fundoscopic examination is mandatory even though papilledema has been ruled out, because IIHWOP is defined as meeting all IIH criteria in the absence of papilledema 1. Baseline visual field testing and ongoing monitoring are essential because vision remains at risk 1, 2.

Critical Diagnostic Considerations

Atypical IIH Features

This patient qualifies as atypical IIH because she is 13 years old (not of typical childbearing age) 1. Atypical patients require more in-depth investigation to ensure no underlying causes 1.

Secondary Causes to Exclude

Medication history is essential: Tetracyclines (including doxycycline), vitamin A, retinoids, steroids, growth hormone, thyroxine, and lithium can cause or exacerbate IIH 3, 4. Concurrent doxycycline with high-dose vitamin A (>10,000 IU daily) should be avoided due to additive risk 2.

Venous Sinus Stenosis

Transverse sinus stenosis on MRV is frequently observed and, although it may be secondary to high pressure rather than causative, its presence reinforces the diagnosis 2, 5.

Initial Treatment

Medical Management

Acetazolamide is first-line medical therapy for patients with mild visual loss, started at a low dose and gradually increased as tolerated 3, 6:

• Weight loss is critical if the patient is overweight, with a goal of 5-10% reduction 3, 6
• Low-sodium diet should be implemented 3, 6
• Topiramate may be considered as an alternative, offering both carbonic anhydrase inhibition and appetite suppression 3

When to Escalate

Evidence of declining visual function requires urgent surgical intervention to preserve vision 1, 2:

• Optic nerve sheath fenestration (ONSF) is effective and safe with fewer complications than CSF diversion 3
• Ventriculoperitoneal shunt is preferred over lumboperitoneal shunt due to lower revision rates 3
• Serial lumbar punctures are not recommended for ongoing management 3

Common Pitfalls

Do not dismiss the diagnosis because papilledema is absent—IIHWOP is a recognized subtype where vision can still be compromised 1. The transient sixth nerve palsy is a red flag that should not be ignored 1.

Do not perform lumbar puncture before excluding venous sinus thrombosis—this can be catastrophic if thrombosis is present 1.

Do not assume symptom resolution means the condition has resolved—patients may remain asymptomatic during recurrence, and ongoing monitoring is essential 3.