Q & A: How Does Human Addison's Compare to the Canine Disease?

I don't know if I should even ask this but a situation in my family has me curious. My sister-in-law was diagnosed with pituitary-dependant Addison's disease over five years ago. She has been treated since that time with florinef and prednisone and has been doing well. Recently she had a recheck and an ACTH stimulation test while on treatment and she had a resting cortisol around 10 µg/dl and post around 20 µg/dl. 

Now she's being weaned off of treatment and told her pituitary and adrenals are fine. I've never done an ACTH stimulation test on an animal I'm treating for Addison's disease after it's diagnosed and was wondering about the rational for doing that. Is human Addison's disease curable? Is there something completely different in human Addison's from the canine disease, or am I just missing something? 

If anyone has an opinion and would like to share I'd appreciate it. Curiosity is getting the best of me. 
Thank you.

My Response:

It sounds to me as if they didn't believe the diagnosis of Addison's disease so they repeated the ACTH stimulation test. Addison's disease doesn't resolve once it develops (in either dogs or humans), and there is no such thing as "pituitary-dependent" Addison's disease.

On a brighter note, its's great news that your sister-in-law is normal!

Couldn't you theoretically get glucocorticoid deficiency from lack of production of ACTH? (Kind of like a central diabetes insipidus dog having a central lesion?)

My Response:

Absolutely. But pituitary ACTH deficiency is "secondary" hypoadrenocorticism, not Addison's disease.

Sorry to be such a stickler about terminology, but when Sir Thomas Addison described the disease that now uses his name, all of the patients had "primary" hypoadrenocorticism with complete destruction of both adrenal cortices.Therefore, the term Addison disease should be restricted to those patients with the primary form of the disorder (ie, those that have both glucocorticoid and mineralocorticoid deficiency).

There is no such disease as pituitary Addison's disease. Why? Because, like we all know, pituitary ACTH deficiency can not cause destruction of the adrenal gland or lead to mineralocorticoid deficiency. ACTH deficiency would only cause cortisol deficiency.

When we use the term Addison's so loosely, it becomes very confusing. It really would be best to avoid the use of the term completely. But we know that will never happen!