Sinus venous stenosis-associated IIHWOP is a powerful risk factor for progression and refractoriness of pain in primary headache patients: a review of supporting evidences

Reported prevalence of idiopathic intracranial hypertension without papilledema (IIHWOP) in series of patients with chronic or transformed migraine is significantly higher than expected; yet, IIHWOP is not included among the risk factors for migraine progression. However, several studies provided evidences suggesting that IIHWOP could represent a possible, largely underestimated, risk factor for progression of pain in migraine and, possibly, in other primary headaches. Data from two recent studies, albeit aimed to different end-points, strongly support this hypothesis. In the first study, conducted on a large series of neurological patients without any sign or symptom of raised intracranial pressure (ICP), including chronic headache, the prevalence of bilateral central venous stenosis at magnetic resonance venography (MRV) was 23% and an IIHWOP at opening pressure was found in 48% of this subgroup (11% of the whole sample) while it was not detected in any of the subjects with normal MRV. This indicates that IIHWOP may be much more prevalent than believed in general population and that it can run without any symptom or sign of raised ICP in most of affected subjects. In the second paper, sinus venous stenosis-associated IIHWOP has been found in about one half of a large chronic primary headache patients series with poor response to treatments and in none of those with normal MRV. Moreover, after the diagnostic lumbar puncture, a transient improvement of headache frequency has been observed in the majority of intracranial hypertensive chronic headache subjects. Taken together, the data of these two recent papers rise the following hypothesis: (1) asymptomatic IIHWOP is much more prevalent than expected in general population; (2) IIHWOP is a powerful and largely unrecognized risk factor for progression of pain in primary headache patients; (3) sinus venous stenosis at MRV is a reliable predictor of raised intracranial hypertension also in asymptomatic patients; (4) sinus venous stenosis has a causative role in IIH pathophysiology. These assumptions share a potential high clinical impact and need to be urgently tested in adequately designed controlled studies.