Spontaneous haemorrhage in subdural hygroma in an Alzheimer’s patient on lecanemab

We report a female patient in her 70s with mild cognitive impairment due to Alzheimer's disease (AD) who developed a left temporal lobar haemorrhage after the third dose of lecanemab, accompanied by non-traumatic haemorrhage in a pre-existing subdural hygroma, and was diagnosed with amyloid-related imaging abnormalities with haemorrhage. The patient exhibited mild verbal paraphasia and word recall difficulty but had no other major neurological deficits. There was no additional intracranial abnormality during the course of hospitalisation. This case highlights the importance of considering subdural haemorrhage as a part of the amyloid-related imaging abnormality spectrum in AD patients with subdural hygromas undergoing amyloid-targeted therapies.