Answer to Q5 : a

This patient has constipation, polyuria of  low specific gravity and no glucose in the urine.

A patient who is polyuric due to lack of ADH will have urine of low specific gravity and osmolality and the serum sodium will be normal to high  BUT constipation is not a feature.

One who has polyuria due to diabetes mellitus WILL have glucose in the urine because that is what pulls out the fluid into the urine. Thus SG  will be high.

Water deprivation test is used to differentiate between polyuria due to Diabetes insipidus (lack of ADH) and polydipsia (primary/psychogenic polydipsia) and both of these have low SG urine as described above but constipation is not a feature of these and polydipsia has a low serum sodium.

Head MRI would be an appropriate answer if there were a diagnosis of DI being entertained.

Lung tumors are well known to cause hypercalcemia but this patient is a non smoker and younger than 40 - also has no pulmonary symptoms -thus having such a low probability to have a lung tumor making a chest x-ray a waste.

In the question I mention that the patient does not have pedal edema because I did not want people to think heart failure which can also be a cause for nocturia.

Hypercalcemia is a diagnosis that presents in patients most commonly while routine screening is being done. It makes the renal receptors for ADH resistant to ADH - a situation like nephrogenic DI. Patients also experience constipation. They may have CNS drowsiness and abdominal pain due to renal stones.