Idiopathic Intracranial Hypertension

Question 1

What is the pathophysiology behind idiopathic intracranial hypertension?

Answer 1

• Impaired absorption of CSF from sub-arachnoid space leads to ↑ICP.
  
  • Aka benign intracranial hypertension, pseudotumor cerebri.

Question 2

Which signs and symptoms are seen in IIH?

Answer 2

• Generalised throbbing headache:
  
  • Worse in the morning and last thing at night.
  • Exacerbated by lying, bending, coughing.
• Visual:
  
  • Symptoms: blurred vision, field loss (‘grey out’) on bending, flashes.
  • Signs: papilloedema, enlarged blind spot, absent venous pulsation on fundoscopy.
• Others:
  
  • Nausea and vomiting.
  • Seizures
  • Cranial nerve 6 palsy leading to diplopia.

Question 3

What are the risk factors for IIH?

Answer 3

• Demographic and lifestyle: female, obese, age 20-40.

* Drugs: tetracycline, minocycline, nitrofurantoin, vitamin A, isotretinoin.

Question 4

Which differential diagnoses might you consider in a patient presenting with symptoms of IIH?

Answer 4

• DDx:
  
  • Raised intracranial pressure
  • Idiopathic intracranial hypertension.
  • Space-occupying lesion (primary or mets).
  • Haemorrhage: subdural, extradural, sub-arachnoid, intra-cerebral.
  • Cerebral venous thrombosis.
  • Cerebral oedema.
  • Malignant hypertension.

Question 5

Which investigations should be carried out in suspected IIH?

Answer 5

• CT or MRI: rule out mass, hydrocephalus, or other cause of ↑ICP. Ideally include CT/MR venography to rule out cerebral venous thrombosis.
  
  • LP: opening pressure >25 cm H20 is diagnostic, 20-25 is borderline.

Question 6

How is IIH managed?

Answer 6

• Weight loss.
  
  • Acetazolamide: carbonic anhydrase inhibitor that reduces CSF production.
  • Ventriculoperitoneal (VP) shunt or optic nerve sheath fenestration if visual function declining.

Question 7

Which complications can occur in IIH and what does the prognosis look like for these patients?

Answer 7

• Relapse is common.

* Permanent blindness from cranial nerve 2 damage. Affects 10% of patients in at least one eye.