headache. The signs that enable optic neuritis to be differentiated from IIH may also be lacking, as affected young children are seldom able to cooperate for Goldman perimetry. Thus, although ophthalmologists may be correct in asserting that 'visual evoked response testing does not have a role in the detection or monitoring of visual dysfunction in IIH', 1 it is a test that may lend valuable support to a clinical suspicion of optic neuritis.
On this care pathway, abnormal fundoscopy often prompts cranial imaging. In an ideal world this will include magnetic resonance (MR) venography and also sequences that are sensitive to white matter disorders, but IIH may only be considered for the first time after exclusion of a mass lesion on imaging that is inadequate to exclude venous thrombosis or optic neuritis. Young macrocephalic children with normal optic discs, especially those with macrocephalic parents, whose scans show plump ventricles and large extra-cerebral spaces, do not have IIH and should not be exposed to the risks of its treatment. Most have benign external hydrocephalus (BEH) and are asymptomatic (with elevated CSF pressures relative to population norms).
CSF composition, including cell count and levels of protein and glucose, must be normal. CSF opening pressure is liable to elevation by anxiety, distress, hyperflexion for lumbar puncture, breath-holding, over-sedation, or general anaesthesia. Reference pressure ranges that take account of being overweight are available for adults but not for children. Conditions other than IIH may lead to swollen discs and elevated CSF pressure, notably optic neuritis. Thus, for every child that truly has IIH, I typically see four or five other children without IIH but with a CSF pressure measurement between 17 and 27cm of CSF. These include healthy children, those with optic neuritis, and those with BEH.
If the evidence base for management of IIH were ice, I would not walk on it, even if I were a duck, and I will not air my views here. We need to reach a sufficient consensus to start the long journey towards a randomized controlled trial of alternative treatments. Incidence figures for paediatric IIH have been hamstrung by diagnostic uncertainty, but the relative rarity of IIH clearly warrants a multi-centre approach. Clear case definition will, therefore, be significant for epidemiological survey and management.
Light in this murky area of clinical practice is badly needed. I wish the BPSU-backed investigators success in achieving consensus. The starting point must be a precise algorithm for diagnosis.