Headache is a near universal sequela of IIH, and can complicate other disorders with raised ICP. We demonstrate a positive relationship between ICP and headache severity and monthly headache days, which has not been noted previously in IIH. Patients with the greatest reduction in ICP over 12 months saw the greatest reduction in headache frequency and severity, and this was associated with improvement of physical functioning in the quality of life SF-36.
We observed that the majority of patients with IIH had migraine-like headaches at baseline, as previously reported.15,18 One patient was headache-free, whereas the majority described severe continuous daily headache pain associated with poor quality of life. Overall headache in patients with active IIH was of moderate pain severity, long daily duration and a mean frequency of 22 days per month, with the associated headache impacting on the individual’s quality of life. These observations are in keeping with broader patients’ views that the chronic daily headache of IIH is very disabling6 and is already known to drive reduction in quality of life in IIH.8
A previous randomized controlled trial in IIH15 classified 68% with migraine or probable migraine and 26% tension-type or probable tension-type headaches. In the present study 86% reported migraine-like headaches and 70% would fulfil the criteria for a diagnosis of chronic migraine. Furthermore, 40% of participants in the present study described aura. In our cohort tension-type headaches were not common, with only one patient fulfilling the IHS criteria.9 This may reflect differences between the types of patients recruited to the two trials, for example the IIHTT15 participants were newly diagnosed patients, whereas the IIH:WT participants reflected a more chronic disease duration (Table 1).
68% of participants reported a prior diagnosis of migraine before being diagnosed with IIH, of whom over half (53%) had been diagnosed with migraine prior to the age of 18 years old and only 11% developed migraine-like headaches following the diagnosis of IIH. This portion of patients with a prior migraine history is considerably higher than that of the general population, where for example one study found the lifetime prevalence of migraine to be 29%.19 A number of interesting observations could be postulated, for example, those with a recent diagnosis of migraine could have been initially diagnosed as migraine instead of IIH, however the portion of those with a very longstanding history of migraine are unlikely to have been misdiagnosed. Given the longevity of migraine in our cohort, some patients may have had chronic migraine before diagnosis of IIH, whereas others may have developed chronic migraine-like headaches following diagnosis. It remains unclear whether diagnosis of IIH in patients with known episodic migraine contributes towards transition to chronic migraine and if this is dependent on central sensitization.
Cutaneous allodynia is reported in over half of all patients with migraine.20 It has not typically been a feature of conditions associated with raised ICP (e.g. brain tumours or hydrocephalus). A previous study reported allodynia in 50% of IIH patients who mostly had a migraine-like headache profile.18 In the present study 92% reported cutaneous allodynia at the maximum headache severity and although this was not associated with headache severity or frequency at baseline, change in allodynia over 12 months was associated with change in ICP.
Headache management is an unmet need in this disease, with no randomised controlled trials to guide treatment options. Only 18 participants were on concurrent headache preventative therapies, whereas 40 fulfilled the criteria for chronic migraine-like headaches, leaving a large portion of patients under treated. Recently the first prospective open label study of a CGRP monoclonal receptor antibody reported substantial improvements at 3 months, which continued for up to 12 months in the reduction of monthly moderate/severe headache days.13 This benefit was seen both in those with and without prior migraine and in those with or without prior existing medication overuse headache.13 Topiramate, a well-known migraine preventative therapy has been evaluated in IIH in the context of the impact on vision, rather than its beneficial effects of reduction of headache disability and is used off label in routine clinical practice.21 However consensus guidelines for IIH placed topiramate as a useful medication for management of headaches in IIH in order to avoid medicines such as beta-blockers and tricyclics that may exacerbate weight gain, a known precipitant of the disease.1
Similar to a previous study approximately a third of participants met the diagnostic criteria for medication-overuse headache at baseline.9 Medication-overuse headache is particularly common in patients with a background of chronic migraine, for example in the United States it has been reported in up to a quarter. However, there are many factors that influence medication-overuse headache.22,23 Advising patients about appropriate usage of headache analgesics and avoidance of opiates is therefore an important part of headache management in IIH.1
The data presented indicates a relationship between increased ICP and increased presence of migraine-type headache. Change in ICP can predict change in headache over time. In a previous randomized controlled trial of those with recent onset IIH (within 2 weeks of presentation) no correlation between headache characteristics and ICP was found over a 6 month follow-up.15 Future studies are required to investigate this complex relationship from the acutely presenting patient to the more chronic phase of IIH headache. ICP monitoring studies may further delineate this complex relationship further. Therapies that have been shown to reduce ICP in animal models, such as GLP-1,24 could be helpful in both reducing headache burden in conditions of raised ICP and weight management in IIH.25