Background Idiopathic intracranial hypertension (IIH) is classically diagnosed in overweight, adolescent females and consists of secondary visual symptoms and signs usually, but not exclusively, in the context of headache. Relationships between CSF opening pressure and clinical features are not straightforward, however, as the recent IIH treatment trial has shown.

Methods IIH patients with CSF opening pressures above 50 cm (“extreme IH”) were identified from the first 100 referrals to our Neuro-Ophthalmology service. Clinical features at presentation and visual parameters were examined.

Results Four patients fulfilled our criterion for “extreme” IH. All were female aged between 16–23 years. Body Mass Index ranged from 28–39. Two were pregnant at presentation and two presented with unilateral VIth cranial nerve palsies. Visual acuity was 6/6 or better in 7 eyes and 6/18 in the remaining eye. Only one patient sustained significant visual field impairment. None conformed to the “fulminant IIH” definition or required surgical management. Importantly, headache was absent in two patients and remained unchanged from a longstanding episodic migraine phenotype in another.

Conclusion Extremely elevated CSF opening pressure observed in a small number of IIH patients may not necessarily be associated with significant headache or visual impairment, suggesting an increased tolerance in these individuals.