Is LP Safe in Suspected IIH with Grade 5 Papilledema Before MR Venogram?

Short Answer: Yes, LP is generally safe - but MRI brain must already be normal, and the specific sequence matters.

The Key Principle: Why LP is Relatively Safe in IIH

"Neuroimaging, ideally brain MRI with contrast, is mandatory before lumbar puncture to rule out an intracranial mass as the cause for symptoms and signs."

• Bradley and Daroff's Neurology in Clinical Practice, p. 2459

Does MRV Need to Come First?

"Cerebral venography (MRV) should also be pursued, if possible, to rule out cerebral venous sinus thrombosis (an IIH mimic)... Neuroimaging, ideally MRI with contrast, is mandatory before LP."

If there is any suspicion of cerebral venous sinus thrombosis (CVST), LP carries a different risk profile. In CVST, therapeutic anticoagulation is the treatment - and if LP is done first, it complicates subsequent anticoagulation.

Grade 5 Papilledema - Does Severity Change Things?

1. Herniation risk is still low in pure IIH even with grade 5, as long as MRI shows no obstructive pathology. The pathophysiology does not create a pressure cone differential.
2. Grade 5 is actually an argument FOR doing LP sooner, not delaying it - it indicates markedly elevated ICP with risk of permanent visual loss. Therapeutic CSF drainage at LP can provide immediate ICP relief and protect the optic nerves.
3. The Alder Hey IIH Clinical Guideline (2024) specifically calls for LP after MRI brain (not necessarily after MRV), and states that if opening pressure is elevated, CSF should be drained to reduce ICP by ~30%.
4. The JNNP consensus guidelines (Mollan et al., 2018) state:

"Following normal imaging, all patients with papilloedema should have a lumbar puncture to check opening pressure and ensure contents are normal."

Practical Recommendation for Your Patient

When Would You Delay LP for MRV?

• Clinical features suggest CVST (thunderclap onset, seizure, focal deficits, male patient, postpartum, hypercoagulable state)
• MRI shows findings suspicious for venous thrombosis (parenchymal hemorrhage in atypical location, hyperdense sinus)
• Your patient has red flag features that make CVST the more likely diagnosis

Bottom Line

Methylene Blue in Methemoglobinemia - Dosing

Standard Dose

• Harrison's 22E confirms: "The usual dose is 1-2 mg/kg IV"
• Tintinalli's Emergency Medicine confirms: "Initial dose is 1 mg/kg (0.1 mL/kg of 1% solution)"

When to Give It

Repeat Dosing

• If no significant improvement within 30-60 minutes, repeat at 1 mg/kg
• For unstable/arrest patients (MetHb >50%): may repeat at 15-60 min

Maximum Dose

7 mg/kg total over 24 hours

• Above 7 mg/kg, methylene blue paradoxically causes methemoglobinemia (it acts as an oxidant at high doses)

Mechanism (Quick Summary)

Critical Contraindication: G6PD Deficiency

• Methylene blue requires NADPH (which depends on G6PD activity)
• In G6PD deficiency: methylene blue is ineffective AND causes hemolytic anemia - do NOT use
• Alternative: IV ascorbic acid (vitamin C), exchange transfusion, or hyperbaric oxygen

Practical Notes

• Follow each dose with 15-30 mL NS flush
• Co-administration of dextrose (1 mEq/kg) helps replenish NADPH cofactors
• Pulse oximetry will show a spurious drop in SpO₂ for 10-30 min after dosing - this is a dye artifact, not true desaturation
• Methylene blue has MAOI activity - avoid with serotonergic drugs (serotonin syndrome risk)
• Urine and skin may turn blue-green - reassure the patient

If Methylene Blue Fails

How to Write Squint (Strabismus) in a Clinical Case

Step 1 - Inspection (Write what you see)

"On inspection, there is a convergent squint (esotropia) of the right eye / divergent squint (exotropia) of the right eye."

Step 2 - Specify Paralytic vs Concomitant

• Concomitant (non-paralytic): Angle of squint remains the same in all directions of gaze. Usually childhood onset, no diplopia.
• Paralytic (incomitant): Angle of squint changes with direction of gaze. Diplopia present. Ask which muscle/nerve is affected.

"The squint is concomitant / paralytic in nature."

Step 3 - Identify the Nerve/Muscle Involved (in Paralytic Squint)

• S Das Clinical Surgery, p. 5809-5817

Step 4 - Cover Test (Mention in Examination)

"On cover-uncover test, the uncovered eye makes a corrective movement to fix the target, confirming the presence of squint."

• Movement inward on uncovering = exotropia
• Movement outward on uncovering = esotropia

Step 5 - Corneal Light Reflex (Hirschberg Test)

"Hirschberg corneal light reflex test shows asymmetric light reflex - the reflex is displaced nasally in the right eye, consistent with exotropia."

How to Write Pupil Examination in a Clinical Case

S - Size

"Both pupils are equal in size, measuring approximately 3 mm in diameter" OR "Right pupil is dilated (6 mm), left pupil is 3 mm"

S - Shape

"Both pupils are round and regular in shape" OR "Right pupil is irregular in shape"

A - Light Reaction (Direct and Consensual)

"Direct and consensual light reflexes are present and equal bilaterally"

R - Accommodation Reflex

"Accommodation reflex is intact bilaterally" OR "Pupil constricts on near vision but not to light - Light-Near Dissociation (Argyll Robertson pupil)"

Full Model Write-Up for Examination

EYES:
- On inspection: Convergent squint of the right eye noted.
- Hirschberg corneal reflex test: asymmetric, reflex displaced 
  temporally in right eye.
- Cover test: Right eye makes inward corrective movement on 
  uncovering - consistent with right esotropia.
- Ocular movements: Full range of movement in all directions / 
  Limitation of abduction of right eye noted.
- Diplopia: Present / Absent.
- Nature of squint: Paralytic / Concomitant.

PUPILS:
- Size: Right 3 mm, Left 3 mm - equal bilaterally.
- Shape: Round and regular.
- Direct light reflex: Present bilaterally.
- Consensual light reflex: Present bilaterally.
- RAPD: Absent / Present on right side (Marcus Gunn pupil).
- Accommodation reflex: Intact bilaterally.

Quick Tip for Viva

• CN III: Ptosis + Externoinferior squint + Dilated pupil (surgical CN III) or normal pupil (medical CN III - diabetes/HTN)
• CN VI: Pure convergent squint, no ptosis, no pupil change
• CN IV: Head tilt to opposite side (to compensate), hypertropia worse on downgaze

Bilateral 6th Nerve (Abducens) Palsy

Clinical Features

• Bilateral convergent squint (both eyes turned inward due to medial rectus unopposed)
• Bilateral failure of abduction (cannot move either eye outward)
• Bilateral horizontal diplopia, worse on lateral gaze
• Patient may adopt a face-turn to compensate
• No ptosis, no pupil change (CN VI has no pupillary fibers)

Why Bilateral? - The Key Anatomical Reason

Causes of Bilateral 6th Nerve Palsy

A - Raised Intracranial Pressure (Most Important Cause)

• Adams & Victor's Neurology: "Isolated unilateral or bilateral sixth nerve palsy with global headache can be the initial manifestation of raised intracranial pressure from any source - including brain tumor, meningitis, and pseudotumor cerebri"

B - Brainstem (Pontine) Lesions

C - Meningeal/Basal Pathology (Bilateral Diffuse)

D - Petrous Apex

• Gradenigo syndrome: Unilateral usually, but bilateral if symmetric - CN VI palsy + retroorbital pain (CN V1) + deafness (CN VIII)
• Caused by: petrous apex osteomyelitis, cholesteatoma, trauma

E - Cavernous Sinus

• Bilateral cavernous sinus thrombosis (rare)
• Bilateral cavernous sinus meningioma
• Pituitary apoplexy

F - Metabolic / Systemic

Investigation Approach

Bilateral CN VI palsy
        ↓
1. MRI Brain (with contrast) - URGENT
   - Exclude mass, pontine lesion, hydrocephalus
2. MRI/MRA of posterior fossa and clivus
3. Fundus exam - papilledema? → raised ICP
4. LP (after MRI clears mass):
   - Opening pressure
   - CSF cells, protein, glucose
   - Gram stain, culture, AFB, India ink
   - Cytology if malignancy suspected
5. Bloods: thiamine, B12, glucose, TFTs
6. Chest X-ray/CT (sarcoid, TB, malignancy)

High-Yield Associations for Exams