MRCP2-1505
A 67-year-old man presents to the medical admissions unit with increasing drowsiness and confusion. He was diagnosed with primary small cell carcinoma of the lung six months ago but declined chemotherapy. His past medical history includes chronic obstructive pulmonary disease, ischaemic heart disease, hypertension, hypercholesterolaemia, and depression.
His wife brought him to the Emergency Department after noticing his increasing drowsiness and confusion over the last few hours. He had been relatively well prior to this. His GP had prescribed Oramorph solution PRN for new onset generalised aches and pains four weeks ago. He had developed abdominal pain, which the GP attributed to opiate-induced constipation and prescribed lactulose 15 ml BD, providing partial relief. He had not experienced weakness, numbness, or speech impairment, and had taken the prescribed dose of oramorph. His current medications include oramorph solution 10mg BD, paracetamol 1g QDS, dihydrocodeine 60mg QDS, lactulose 15 ml BD, aspirin 75mg OD, atorvastatin 20mg ON, bisoprolol 2.5mg OD, Ramipril 2.5mg OD, and furosemide 40 mg OD.
On examination, the patient was drowsy with a GCS of 12 (E 3 M5 V4). His blood pressure was 102/68, heart rate 58 bpm, respiratory rate 10/min, oxygen saturations of 95% on air, and temperature 36.6ºC. Cardiovascular and respiratory systems were unremarkable. Examination of his central nervous system revealed normal sized pupils, and no focal neurological signs were found. There was no evidence of neck stiffness, and Kernig’s sign was negative. The patient was uncooperative with an abbreviated mental state examination.
Which investigation is most likely to provide a diagnosis of the underlying cause?