What are the causes of Cushing’s syndrome?

A 29-year-old female presented with progressive swelling over the body, weight gain, menstrual irregularity. On examination, her BP was 160/100 mm Hg, pulse rate 86/min, weight 88 kg, height 155 cm. Buffalo hump was present with broad purplish striae over the abdomen. Proximal muscle weakness was present. Her investigations revealed Hb 12.6 g%, fasting blood sugar (FBS) 170 mg%, creatinine 0.9, Na 140 mEq/L, K 3.4 mEq/L (Fig. 2.1).

What are the causes of Cushing’s syndrome?