BACKGROUND: Stroke is the major cause of disability and the fifth leading cause of death in the United States. In 30–40% of strokes the etiology remains uncertain or unknown. Identifying the cause of a cerebrovascular event offers the opportunity for an intervention that may decrease the risk of future stroke and thus prevent the resultant impairment.

CASE REPORT: We report the case of an 80-year-old African American woman with a prior right middle cerebral artery stroke, who presented to the hospital with new left-sided weakness and was found to have a new right-sided frontal lobe infarct. Twenty-four hour Holter monitoring performed during this hospitalization and prior 24-h electrocardiogram (ECG) recording did not reveal an arrhythmia. However, the patient was found to have an isolated episode of atrial fibrillation (AF) during an echocardiogram as part of the evaluation for stroke etiology.

CONCLUSIONS: AF is an important and treatable cause of recurrent stroke and needs to be ruled out by thorough evaluation before the diagnosis of cryptogenic stroke is assigned. Despite meticulous diagnostic work-up, many strokes caused by paroxysmal AF remain undetected and longer ECG monitoring (>24 h) may be required.

Keywords: Atrial Fibrillation - ultrasonography, Aged, 80 and over, Echocardiography, Frontal Lobe - blood supply, Stroke - diagnosis