Summary

Acute confusion is a common symptom of physical illness in the older patient. In the majority, it is transient and resolves on treatment of precipitants. In a subset of patients, however, neurological decline is progressive, raising concern about a serious underlying cause. We describe the case of a 71-year-old woman who developed progressive cognitive impairment following insertion of a permanent pacemaker for sinoatrial arrests. An initial diagnosis of delirium secondary to a urinary tract infection was suspected; however, the patient became increasingly confused despite treatment. Laboratory tests revealed serum anti-Hu paraneoplastic antibodies, and CT chest identified an occult lung tumour. Cervical lymph node histopathology confirmed a diagnosis of small cell carcinoma of the lung. Although a rare cause of confusion, paraneoplastic encephalomyelitis should be recognised early to allow timely identification and treatment of the associated cancer.