A 35-year old male with a history of severe bronchial asthma for several months now complains of weight gain and the development of purple stretch marks. Physical examination showed BP - 149/95 mmllg. supraclavicular fullness. The skin was thinned out with areas of bruising. Neurological examination revealed deceased strength in the proximal muscles. Laboratory investigation showed reduced serum coisol and reduced plasma ACTH. An electrolyte workup in this patient will most likely reveal His condition is most likely due to a/an