Back to the Plaquenil:
It is possible that within the Lupus community itself, this drug is "commonly" used or at least tried. Same with some of the other autoimmune conditions.
Also recently the new biologic agents for all the inflammatory type issues, where Plaquenil was previously used, are eclipsing the older agent.
Here is something interesting. I have this redness on my arms, which resulted from a severe reaction to the water on vacation, which blistered me. (a professor at WSU near me thought it was a reaction to an algae in the water...I only get it when the water turns warmer from being really cold. Otherwise I can go in the water and have sun and have no blisters or redness).
So I found this disorder recently:
http://dermnetnz.org/immune/rem.html
Guess what the ONLY treatment is? Plaquenil! In fact this condition is not well understood, and is not exactly a rash, as we know it. It blanches, and goes away when I lie down, but when I stand up or sit up gravity makes it red again. It is a vascular thing therefore in the deeper skin. It is a little less acute after about 4 yrs now, but according to what I am finding about it, is related to Lupus...but is "not Lupus"...in other words not understood. (Lupus tests negative, and I've had two Lupus investigations in the past which were negative both times).
I've hesitated to go to the dermatologist as my internist suggested, because this redness/rash does not spread, does not weep (you cannot feel it when you put your hand over it), it does not hurt, burn, itch, weep, bleed, or flake. In fact my skin is soft and normal except for the redness, which blanches on pressure. At this point it is not doing anything. Why expose myself to some potentially toxic treatment?
In fact I've been doing high dose Biotin for over a month now, and it seems to be fading the redness some. I am hopeful I can heal it this way.
Back to ACE.... I believe it is important because of your lung issues, Idiopathic, to have sarcoid ruled out. Sarcoid is tissue which is inflamed and deposited in organs and the CNS and needs to
be ruled out for your PN too. (neuro Sarcoid). So if you are low in ACE, then that is one potential you won't have to follow up on at this point.