The Daily Differential — Monday, August 17, 2026

Idiopathic Intracranial Hypertension

IIH can silently destroy the optic nerves while the patient remains neurologically well. The management fork is not headache severity—it is the speed and degree of visual loss.

Also known aspseudotumor cerebri · benign intracranial hypertension · pseudotumor

By the Blue Fish Med Desk Aug 17, 2026 · Phoenix

0:00 / –:–– AI‑generated audio

A 27-year-old woman sits forward in the dim room, pressing her fingers against the temples as the fluorescent lights flicker overhead. She describes weeks of daily pressure-like headaches, brief “gray-outs” when standing, and a rhythmic whooshing in both ears. Her BMI is 38, and visual acuity is slightly reduced; the funduscopic view is blurred by elevated optic discs. The question is whether her vision is already in danger—and the next move has not yet been made.

— What’s your move? Read on.

Before you read

What must be excluded before a lumbar puncture?
When is medication no longer enough?

When to Think of It

Typical presentation: obese woman of childbearing age with daily headache, transient visual obscurations, pulsatile tinnitus, binocular horizontal diplopia from CN VI palsy, and papilledema. IIH requires papilledema, normal neurologic examination apart from cranial nerve abnormalities, normal neuroimaging, and elevated CSF opening pressure with otherwise normal CSF.

Sick or Not Sick

Sick vs. not sick: Is vision actively deteriorating? The single call that matters most is whether there is severe or rapidly progressive visual loss, which requires urgent ophthalmology/neurosurgical involvement rather than outpatient treatment.

The First Fifteen Minutes

Assess visual acuity, color vision, visual fields, pupils, ocular motility, and fundus; involve ophthalmology urgently if visual function is impaired.
If papilledema is suspected, obtain MRI brain with venography, or CT/CT venography if MRI is unavailable, before LP—to exclude mass effect and cerebral venous sinus thrombosis.
After safe imaging, perform LP with lateral-decubitus opening pressure and CSF analysis. An opening pressure ≥25 cm H₂O in adults supports IIH, interpreted in clinical context.
If imaging excludes mass and the patient has significant symptoms but no fulminant visual loss → acetazolamide 500 mg PO or IV, because carbonic anhydrase inhibition reduces CSF production. Dose escalation is often needed; check renal function, bicarbonate, electrolytes, and pregnancy status.
If acute severe headache requires analgesia → acetaminophen 1,000 mg PO/IV; avoid opioids, which worsen chronic headache and obscure neurologic reassessment.
Do not give empiric steroids routinely; they can cause weight gain and rebound intracranial hypertension. Steroids are only a short bridge in selected fulminant cases under specialist direction.

Definitive Care & Disposition

Weight loss is disease-modifying; even 5–10% loss can improve pressure, and bariatric surgery may be considered for severe obesity. Ophthalmology follows formal visual fields and optic-disc findings. Topiramate 25 mg PO nightly, titrated gradually toward 50 mg PO twice daily, may help weight loss and migraine phenotype; dose variability and contraindications warrant checking Lexicomp, UpToDate, or local protocol. Progressive visual loss requires urgent optic-nerve sheath fenestration, CSF diversion, or selected venous-sinus stenting. Stable patients with reassuring vision may be discharged only with expedited neuro-ophthalmology follow-up; fulminant visual loss requires admission.

How This One Kills

The fatal error is accepting a normal CT head as reassurance, missing cerebral venous thrombosis or papilledema, and discharging a patient whose optic nerves are progressively infarcting.

The Differential — What Else Looks Like This

Cerebral venous sinus thrombosis — thrombosis on venography or a prothrombotic context; confusing it with IIH misses anticoagulation and the underlying cause.
Migraine — no papilledema or elevated opening pressure; labeling papilledema as migraine risks permanent blindness.
Optic neuritis — painful monocular visual loss and color desaturation rather than pressure-related transient obscurations; confusing them delays targeted evaluation.
Malignant hypertension — markedly elevated BP with retinal hemorrhages/exudates; treating only intracranial pressure misses systemic end-organ injury.

The Second-Day Story

Older adults, men, patients without obesity, and patients with chronic headache may not fit the classic profile. Papilledema can be subtle, and visual complaints may be described only as “blurry” or “off balance.” Recheck the optic nerves, obtain formal visual fields when possible, and do not reject IIH solely because the demographic pattern is imperfect.

Back to Our Patient

Back to the 27-year-old woman with pulsatile tinnitus and blurred optic discs: her papilledema and transient visual obscurations make IIH a vision-threatening diagnosis until proven otherwise. She has urgent venous imaging before LP; imaging excludes mass and thrombosis, and her opening pressure is 34 cm H₂O with normal CSF. Her visual fields show early peripheral loss, so acetazolamide 500 mg IV is started, ophthalmology and neurosurgery are consulted, and she is admitted for rapid visual monitoring rather than discharged as a headache patient.

Patient Presentation to Attending

How you’d present this patient on the floor — tight, pertinent positives and negatives, no rambling

“This is a 27-year-old woman with obesity presenting with several weeks of daily pressure-like headaches, pulsatile tinnitus, and transient bilateral visual dimming. She denies fever, focal weakness, persistent diplopia, or a thunderclap onset, but reports worsening symptoms with position changes. Exam shows reduced visual acuity, blurred optic discs bilaterally, and no focal motor or sensory deficit. I’m concerned for papilledema from idiopathic intracranial hypertension versus cerebral venous sinus thrombosis. I’ll obtain urgent MRI with venography, then perform a lumbar puncture if there is no mass effect, start acetazolamide after safe imaging, and admit her for ophthalmologic visual-field monitoring because her vision may be threatened.”

Study Directive

Draw the IIH diagnostic pathway from papilledema → venous imaging → safe LP → opening pressure/CSF interpretation.
Practice documenting visual acuity, color testing, pupils, fields, and ocular motility in three simulated cases.
Review acetazolamide contraindications and titration using Lexicomp or institutional protocol.
Compare IIH, cerebral venous thrombosis, migraine, and malignant hypertension in a four-column differential.
State the indications for optic-nerve sheath fenestration and CSF diversion without looking them up.

Recent Literature

Review or guideline Diagnosis and treatment of idiopathic intracranial hypertension
Raoof N, Hoffmann J · Cephalalgia, 2021 · PMID 33631966 · cited 100×

A practical reference for recognizing papilledema, excluding secondary causes with neuroimaging and venography, confirming elevated opening pressure, and initiating vision-preserving treatment.

Full text · open access

3 of 4

Elissa’s Story

Anti-NMDA receptor encephalitis often begins with psychiatric symptoms and progresses to seizures, dyskinesias, autonomic instability, and hypoventilation....

Listen: EM:RAP podcast →

0:00 / –:–– AI‑generated audio

The Case

A 22-year-old woman is brought in by her mother after three weeks of insomnia, whispered conversations with unseen people, and increasingly bizarre behavior. In the department she alternates between a fixed stare and sudden agitation, her jaw clenches, and her arms briefly twist into an unusual posture. Her temperature is 38.1°C, and the family mentions a recent “new psychiatric problem,” but no one can explain the rapid neurologic decline. The cause of her altered behavior remains unnamed while the next seizure may be forming.

Before You Read

When does a psychiatric-appearing presentation become autoimmune encephalitis?
What must be treated before antibody results return?
Which complications require ICU-level monitoring?

Why It Matters

Anti-NMDA receptor encephalitis often begins with psychiatric symptoms and progresses to seizures, dyskinesias, autonomic instability, and hypoventilation. Delayed recognition leads to aspiration, status epilepticus, dysautonomia, and prolonged neurologic disability.

When to Think of It

Subacute psychiatric change over days to weeks—anxiety, paranoia, hallucinations, insomnia, mania, or catatonia—followed by memory deficits, seizures, abnormal movements, decreased consciousness, or autonomic instability. Young women are classic, and ovarian teratoma is an important associated tumor, but any sex or age can be affected.

Sick or Not Sick

Sick vs. not sick: Is there evolving encephalitis with seizures, impaired airway protection, dyskinesia, or autonomic instability? Abnormal vitals, fluctuating consciousness, refractory agitation, hypoventilation, or frequent seizures require ICU-level care and early neurology involvement.

The First Fifteen Minutes

Check glucose, temperature, oxygenation, ECG, electrolytes, renal/hepatic function, CK, pregnancy test, and toxicologic exposures; dyskinesias and agitation can rapidly produce rhabdomyolysis.
If convulsing or in status → lorazepam 0.1 mg/kg IV, maximum 4 mg, because GABA-A activation rapidly terminates seizure activity.
If seizures persist after benzodiazepine → levetiracetam 60 mg/kg IV, maximum 4,500 mg, because rapid loading provides sustained antiseizure activity with limited hemodynamic effect. Dose and maximum should be checked against local status protocol.
If encephalitis is plausible and lumbar puncture or imaging will be delayed → acyclovir 10 mg/kg IV every 8 hours, renal-adjusted, because early HSV treatment reduces neurologic injury. Add empiric bacterial meningitis therapy when clinically indicated: ceftriaxone 2 g IV every 12 hours plus vancomycin 15–20 mg/kg IV every 8–12 hours, with pharmacy-guided dosing and levels.
For dangerous agitation threatening the patient or staff → lorazepam 1–2 mg IV/IM, cautiously, because it reduces agitation and catatonia; repeated sedation requires airway monitoring. Avoid reflexive antipsychotic escalation when fever, rigidity, dysautonomia, or catatonia suggest encephalitis.
Treat hypoglycemia if present with dextrose 25 g IV, because inadequate cerebral glucose worsens encephalopathy.

Definitive Care & Disposition

Admit patients with suspected autoimmune encephalitis, usually ICU if seizures, dysautonomia, hypoventilation, severe dyskinesia, or impaired airway protection are present. Obtain MRI brain, EEG, LP with cell count, protein, glucose, cultures, HSV/VZV PCR, oligoclonal bands, and autoimmune encephalitis antibodies in CSF and serum; do not delay empiric therapy for antibody results. After infection is reasonably addressed, neurology typically initiates methylprednisolone 1 g IV daily for 3–5 days, often with IVIG 2 g/kg total divided over 2–5 days or plasma exchange; specialist dosing and contraindication review are essential. Screen for ovarian teratoma or other malignancy with pelvic imaging and age-appropriate evaluation. Refractory disease may require rituximab or cyclophosphamide.

How This One Kills

The specific catastrophe is treating escalating agitation with dopamine blockade while missing anti-NMDA encephalitis, worsening rigidity, dysautonomia, QT prolongation, seizures, and malignant catatonia.

The Atypical Presentation

Some patients have months of isolated anxiety, insomnia, depression, or “behavioral” decline before clear neurologic signs. Others are afebrile or have normal initial MRI and CSF. The diagnostic signal is the trajectory: new psychiatric symptoms plus seizures, abnormal movements, cognitive decline, catatonia, or autonomic changes should prompt neurologic evaluation even when the mental-health history appears persuasive.

Back to Our Patient

Back to the 22-year-old woman: her subacute psychiatric change followed by dyskinesia, fever, and fluctuating consciousness is autoimmune encephalitis until proven otherwise, not a primary psychiatric disorder. She has normal glucose, episodic seizures on EEG, inflammatory CSF, and no mass lesion; acyclovir and bacterial coverage are started while infectious testing is pending, and she receives benzodiazepine treatment for seizures. She is admitted to the ICU for airway and autonomic monitoring, then undergoes pelvic imaging showing an ovarian teratoma and begins specialist-directed immunotherapy after infectious disease is addressed.

Patient Presentation to Attending

“This is a 22-year-old woman with three weeks of insomnia, hallucinations, and behavioral change now complicated by fever, jaw clenching, abnormal posturing, and fluctuating consciousness. She has no known antipsychotic exposure, and the family reports a rapidly progressive course rather than a stable psychiatric illness. Her glucose is normal, but she has intermittent seizure-like activity and dyskinesia without a focal deficit. I’m concerned for anti-NMDA receptor encephalitis, with HSV encephalitis, toxicologic disease, and NMS as alternatives. I’ll treat any seizure immediately, start empiric acyclovir and meningitis coverage while obtaining MRI, EEG, and LP, involve neurology and infectious disease, and admit her to the ICU for airway and autonomic monitoring.”

Study Directive

Memorize the sequence: psychiatric prodrome → seizures/cognition → dyskinesia → dysautonomia/hypoventilation.
Build an initial encephalitis order set from memory, including CSF studies, EEG, MRI, and empiric antimicrobials.
Compare anti-NMDA encephalitis, HSV encephalitis, NMS, serotonin syndrome, and malignant catatonia.
Practice status-epilepticus medication dosing with a 60-kg and 90-kg adult.
Review ovarian teratoma screening and first-line immunotherapy with neurology or an institutional protocol.

Key Medications

Acyclovir: 10 mg/kg IV every 8 hours for suspected HSV encephalitis; renal adjustment is mandatory.
Ceftriaxone: 2 g IV every 12 hours when empiric bacterial meningitis coverage is indicated.
Vancomycin: 15–20 mg/kg IV every 8–12 hours, adjusted to renal function and institutional AUC/trough protocol; check pharmacy reference.
Lorazepam: 0.1 mg/kg IV, maximum 4 mg for status; 1–2 mg IV/IM for severe agitation or catatonia with airway monitoring.
Levetiracetam: 60 mg/kg IV, maximum 4,500 mg for ongoing seizures; confirm local protocol.
Methylprednisolone: 1 g IV daily for 3–5 days is common specialist therapy; timing and contraindications require neurology consultation.
IVIG: total 2 g/kg divided over 2–5 days; dosing varies by indication and ideal/adjusted body weight—check Lexicomp, UpToDate, or institutional protocol.
Pediatric encephalitis treatment is weight-based and requires pediatric infectious disease, neurology, and ICU involvement.

High-Yield Pearls

New psychosis plus seizures or abnormal movements is neurologic disease until proven otherwise.
Normal MRI does not exclude autoimmune encephalitis; EEG and CSF may provide the first objective abnormalities.
Antipsychotic-related worsening rigidity, fever, and dysautonomia should increase—not decrease—concern for an underlying encephalitis.

The Mimics

Primary psychosis or mania — no progressive neurologic signs, seizures, dyskinesia, or autonomic instability; mislabeling encephalitis delays immunotherapy.
Neuroleptic malignant syndrome — recent dopamine antagonist exposure with marked rigidity, hyperthermia, and CK elevation; confusion leads to the wrong trigger-focused treatment.
Serotonin syndrome — serotonergic exposure, clonus, and hyperreflexia; confusing the two can miss encephalitis and tumor screening.
HSV encephalitis — fever, temporal findings, seizures, and inflammatory CSF; failure to give acyclovir risks irreversible injury.

Board Question

A 20-year-old woman develops paranoia, insomnia, seizures, orofacial dyskinesias, and episodes of tachycardia and hypoventilation over one month. MRI is normal. Which associated condition should be specifically sought?

AOvarian teratoma
BPituitary macroadenoma
CCerebral aneurysm
DPheochromocytoma

Reveal answer

Correct: A

Ovarian teratoma. Anti-NMDA receptor encephalitis is strongly associated with ovarian teratoma, particularly in young women. Tumor identification and removal are important components of definitive treatment.

Recent Literature

Review or guideline European Academy of Neurology/Peripheral Nerve Society Guideline on diagnosis and treatment of Guillain-Barré syndrome
Eur J Neurol, 2023 · cited 209×

Use this guideline to recognize Guillain-Barré syndrome early, monitor for respiratory failure and autonomic instability, and initiate IVIG or plasma exchange without waiting for every diagnostic test to become positive.

Full text · open access

TheDaily Differential

Idiopathic Intracranial Hypertension

When to Think of It

Sick or Not Sick

The First Fifteen Minutes

Definitive Care & Disposition

How This One Kills

The Second-Day Story

Study Directive

Recent Literature

More in Today's Issue

Transient Global Amnesia

Elissa’s Story

Hot and Altered

Yesterday’s Differential

Journal Watch

SPICE III Trial: Does Early Dexmedetomidine Improve Survival in Mechanically Ventilated ICU Patients?

Podcast Picks

Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Spinning Plates

Critical Care Corner

Intracranial hypertension signs

Pharmacology Corner

Ertapenem

Diltiazem

ECG of the Day

Case of the Day