A 36-year-old man has been complaining of marked weakness, low appetite, and nausea for the last year, year and a half. Within the last year he has lost 10 kg of body mass. The skin is darkened, especially on his face, neck, and arms. Skin folds and nipples are hyperpigmented, there are pigment spots on the patient’s inner thighs. Pulse is 60/min., blood pressure is 80/50 mm Hg. What is the provisional diagnosis?