Review Question - QID 212458

A 54-year-old woman comes to the clinic for an annual check-up. She has no other complaints except for some weight gain over the past year. Her last menstrual period was 8 months ago. “I started eating less since I get full easily and exercising more but just can’t lose this belly fat,” she complains. She is sexually active with her husband and does not use any contraception since “I am old.” She denies vaginal dryness, hot flashes, fevers, abdominal pain, or abnormal vaginal bleeding but does endorse intermittent constipation for the past year. Physical examination is unremarkable except for some mild abdominal distension with fluid wave. Laboratory findings are as follows:

Serum:
Na+: 138 mEq/L
Cl-: 97 mEq/L
K+: 3.9 mEq/L
Urea nitrogen: 21 mg/dL
Creatinine: 1.4 mg/dL
Glucose: 120 mg/dL
B-hCG: negative

What is the most likely diagnosis for this patient?