26th April 2024

A 38-year-old man presents with a six-month history of progressive fatigue, muscle weakness, and unintentional weight loss of 10 kg.

A 38-year-old man presents with a six-month history of progressive fatigue, muscle weakness, and unintentional weight loss of 10 kg. He also reports darkening of his skin, particularly in sun-exposed areas, scars, and creases. He mentions experiencing dizziness when standing and a craving for salty foods. His blood pressure is 95/60 mmHg. His past medical history is unremarkable, and he is not on any medications.

Investigations:

Serum sodium 128 mmol/L (135-145)

Serum potassium 5.6 mmol/L (3.5-5.1)

Serum cortisol 85 nmol/L at 8 AM (171-536)

ACTH 220 pg/mL (10-60)

Which is the most likely diagnosis?