Not all strokes are strokes an example of diagnostic confirmation bias

Abstract

A72-year-oldwomanpresentedwithacomplexpartialseizureandrighthemiparesis,afterafour-weekhistoryofcognitivedecline,apraxiaand speech disturbance. She previously had chronic lymphocytic leukaemia (CLL) and had finished chemotherapy one year prior to presentation. She was receiving monthly intravenous immunoglobulins for bronchiectasis. Brain imaging showed hypodensity in the left temporo-parietal regions. Cerebrospinal fluid was positive for the JC virus, leading to a diagnosis of progressive multifocal leucoencephalopathy (PML). She remains alive, eight months following initial presentation. The case was valuable for reflective practice in avoiding diagnostic (confirmation) bias because the treating team pursued an incorrect diagnosis of stroke and secondary seizure after radiology findings appeared consistent with this. Additionally, PML has not previously been reported in individuals with CLL receiving immunoglobulin therapy, and may explain the relatively benign course in this individual patient. This offers a potential research question for disease modifying treatments in PML.