A 36-year-old woman presents with sudden onset of quadriplegia and dizziness. Physical examination: alert, facial flushing, generalized hyperpigmentation, acne vulgaris, perioral hirsutism, lanugo hair hyperplasia. Thickened subcutaneous fat in the chest and abdomen, with 1.0cm wide purple striae on the lower abdomen. Fasting blood glucose (FBG) 10.2mmol/L, urinary 17-hydroxycorticosteroids (17-OHCS) 58μmol/24h (21mg/24h). Which of the following is the most likely diagnosis?