Idiopathic Intracranial Hypertension

What is it?

• Unclear! Overproduction of CSF vs decreased absorption from the arachnoid granulations.

How often will I see it?

• This isn't super uncommon. The incidence is high enough that you'll see roughly one patient with IIH for every 25-50 primary headache patients

Why is it can't miss?

• Delayed diagnosis leads to blindness from unchecked elevated intracranial pressure on the optic nerves

How does it present?

• Headache 92-94%
• Visual disturbances 30-68% (eg no visual disturbance in up to 32%)
• “Pulsatile tinnitus” 64-87%
• Abducens palsy (diploplia) 20%
• Neck/shoulder/arm pain 44-48%
• Numbness 24%
• Papilledema “Virtually all cases”

How do I diagnose?

• LP with opening pressure >25 cm H20
• No other cause of elevated pressure (i.e. infection, tumor)
• A CTV or MRV to rule out cerebral venous thrombosis (another cause of elevated ICP) is mandatory

As a bonus, here is a neat chart with more "can't miss" headaches, along with the consequences of missed diagnosis. Consider them in your differential, read up on them, and hopefully you won't miss the next "can't miss" headache!