ABSTRACT
OBJECTIVES: Defects in human cognition commonly result in clinical reasoning failures that can lead to diagnostic errors. CASE PRESENTATION: A 43-year-old female was brought to the emergency department with 4-5 days of confusion, disequilibrium resulting in several falls, and hallucinations. Further investigation revealed tachycardia, diaphoresis, mydriatic pupils, incomprehensible speech and she was seen picking at the air. Given multiple recent medication changes, there was initial concern for serotonin syndrome vs. an anticholinergic toxidrome. She then developed a fever, marked leukocytosis, and worsening encephalopathy. She underwent lumbar puncture and aspiration of an identified left ankle effusion. Methicillin sensitive staph aureus (MSSA) grew from blood, joint, and cerebrospinal fluid cultures within 18 h. She improved with antibiotics and incision, drainage, and washout of her ankle by orthopedic surgery. CONCLUSIONS: Through integrated commentary on the diagnostic reasoning process from clinical reasoning experts, this case underscores how multiple cognitive biases can cascade sequentially, skewing clinical reasoning toward erroneous conclusions and driving potentially inappropriate testing and treatment. A fishbone diagram is provided to visually demonstrate the major factors that contributed to the diagnostic error. A case discussant describes the importance of structured reflection, a tool to promote metacognitive analysis, and the application of knowledge organization tools such as illness scripts to navigate these cognitive biases.