MSRA-0484

A 35-year-old patient is admitted with vomiting and abdominal pain. He was noted to have marked buccal pigmentation.
On examination, he is dehydrated. His pulse is 95 beats per minute, while his blood pressure (BP) is 100/70 mmHg.
Investigations reveal the following:
Investigation Result Normal values
Glucose 3.5 mmol/l 3.9–7.1 mmol/l
Sodium (Na+) 130 mmol/l 135–145 mmol/l
Potassium (K+) 4.2 mmol/l 3.5–5.0 mmol/l
Urea 7.8 mmol/l 2.5–7.1 mmol/l
Creatinine (Cr) 95 µmol/l 50–120 µmol/l
Which of the following is the most likely diagnosis?