Occult primary brain cancers manifesting in the aftermath of ischaemic and haemorrhagic stroke

Symptoms of occult brain cancer may mimic stroke. Misdiagnosis may lead to improper treatment and delayed diagnosis. We characterised strokes associated with occult primary brain cancer and determined risk that ischaemic and haemorrhagic strokes are associated with occult primary brain cancer.Patients and methods All patients with incident stroke in Denmark 2003–2015 were identified through the Danish Stroke Registry (n = 85,893) and matched 1:10 on age and sex to the Danish background population without a stroke history (n = 858,740). This cohort was linked to the Danish Cancer Registry and prevalence of occult primary brain cancer defined as the event of previously unknown primary brain cancer during a one-year follow-up was estimated. We used Cox regression models to study risk of occult primary brain cancer in comparison to the background population.Results Of 77,484 patients with ischaemic strokes, 39 (1 in 2000) were associated with primary brain cancer; of 8409 with haemorrhagic strokes, it was 126 (1 in 66). In the background cohort, 205 (1 in 4000) had occult primary brain cancer. The multivariate stroke risk factor analysis showed that patients with occult primary brain cancer differed significantly from those without occult primary brain cancer indicating they might have stroke mimics rather than true strokes. Discussion and conclusions: Strokes associated with occult primary brain cancer tend to be stroke mimics rather than true strokes. Primary brain cancer is rare in patients with ischaemic stroke (1 in 2000); risk that misdiagnosis results in maltreatment is, therefore, very low. Occult primary brain cancers are mainly found among patients with haemorrhagic stroke; they are not uncommon (1 in 66) and should always be kept in mind.