20th July 2023

A 58-year-old Caucasian man presents to the emergency department with a 4-month history of gradually worsening memory

A 58-year-old Caucasian man presents to the emergency department with a 4-month history of gradually worsening memory and a 5-day history of abnormal facial movements. His wife reported that he had been gradually losing weight over this time. His past medical history includes a 3-year history of intermittent joint pains affecting his hands and knees, hypertension and hyperlipidaemia. He takes amlodipine 5mg OD and atorvastatin 40mg ON. He has not travelled abroad in the last 2 years. He is an ex-smoker and previously worked as a rubbish collector. His observations are as follows: heart rate (HR) 89 bpm and regular, blood pressure (BP) 155/85 mmHg, respiratory rate (RR) 15, oxygen saturation 98% on room air and temperature is 37.9°C. On examination, he is disorientated to time and place. He has generalised mild abdominal pain on deep palpation without evidence of peritonism. He has enlarged lymph nodes in his groin bilaterally. Neurological examination reveals rhythmic convergent eye movements with synchronised opening and closing of the jaw. Blood tests reveal a normocytic anaemia, normal white cell count and a raised CRP. A CT head is normal. A lumbar puncture is performed, with CSF analysis coming back positive for a gram positive rod.

Based on the clinical presentation and investigation results, what is the most likely causative pathogen?

Select the SINGLE most appropriate option from the list below. Select ONE option only.