Paediatricsniche
A 10-day-old boy born at term is brought in with two days of poor feeding, vomiting and lethargy, and today is floppy and grey. He is afebrile, with a heart rate of 180/min and a capillary refill of 4 seconds. His genitalia are normal for a male though the scrotum appears darkly pigmented. Results: sodium 121 mmol/L (135–145), potassium 7.1 mmol/L (3.5–5.0), glucose 2.1 mmol/L, bicarbonate 12 mmol/L, urea 9 mmol/L, C-reactive protein 3 mg/L. Blood cultures and CSF taken on arrival are subsequently negative.
Which one of the following is the most likely diagnosis?