A 38-year old woman recently returned from a 6 month business trip to Hong Kong. Shortly after returning, she was investigated for a sinus problem and imaging revealed a pituitary microadenoma. Review of systems did not reveal any other symptoms. She did not have any other medical problems and was not taking any medications.
Her physical examination was unremarkable including normal postural blood pressure.
A pituitary hormonal profile was ordered and was normal except for a morning cortisol level of 40.
What is your differential diagnosis for this low cortisol level?