Subarachnoid haemorrhage during premenopausal dienogest therapy in a patient with multiple risk factors.

We present the third case of subarachnoid haemorrhage (SAH) during dienogest (DNG) therapy documented in Japan. A woman in her 40s with a history of smoking and a family history of SAH developed a sudden severe headache and was diagnosed with SAH. Angiography revealed a ruptured anterior communicating artery aneurysm (9.4 mm), which was successfully treated with a Woven EndoBridge. DNG induces a hypooestrogenic state, with serum oestradiol levels dropping to 30 pg/mL after 1 year, potentially increasing the risk of aneurysm rupture. We revised our protocol accordingly to screen for SAH risk factors and perform magnetic resonance angiography (MRA) on patients with a relevant family history. Among the 120 patients screened, 10 patients had a family history of SAH and underwent MRA, which led to the detection of one unruptured aneurysm. DNG therapy was subsequently discontinued. These findings underscore the importance of assessing cerebral aneurysm risk before initiating DNG therapy.