A 35-year-old mother of two is brought to the Emergency Department by her husband. She has been experiencing severe sore throat over the past few days, and has deteriorated on the morning of admission complaining of severe neck stiffness and a headache. She has no past medical history of note; her only medication is the combined oral contraceptive pill.
On examination, she is pyrexial at 38.9 °C. Her blood pressure is 90/50 mmHg and her pulse is 105 bpm and regular. Her Glasgow Coma Scale (GCS) score is 13, she has obvious meningism, and you notice a generalised purpuric rash.
Haemoglobin (Hb) 110 g/l 120–160 g/l
White cell count (WCC) 18.5 × 109/l 4–11 × 109/l
Platelets (PLT) 200 × 109/l 150–400 × 109/l
Sodium (Na+) 138 mmol/l 135–145 mmol/l
Potassium (K+) 3.8 mmol/l 3.5–5.0 mmol/l
Creatinine (Cr) 80 µmol/l 50–120 µmol/l
C-reactive protein (CRP) 250 mg/l 0–10 mg/l
Glucose 6.5 mmol/l 3.9–7.1 mmol/l
What is the most appropriate next step?