A 76-year-old Chinese man presented with two falls in a day and non-specific symmetrical lower limb weakness. This was not associated with anorexia, vomiting, syncope or seizures. Five days prior, he had consulted his general practitioner for herpes zoster and was prescribed oral acyclovir 800mg 5 times a day. His background medical history included ischaemic heart disease for which he had undergone coronary artery bypass surgery, diabetes mellitus, hypertension and dyslipidemia. There had been no recent change to his medication list of Aspirin, Bisoprolol, Amlodipine, Metformin, Atorvastatin and Lisinopril.