As a few others have noted, DNP will flatten you out quickly. I never lost any muscle while using it. I love when you stop, it's so nice how the muscles start to fill back up....though it takes a little time.
In theory muscle volume aka sacroplasmic fluid of the muscles cells are a part of your muscle, its just very easy to loose/gain in short periods. But like aphexa stated you get a rebound effect that actually more than makes up for the loss of volume/fullness.
Used it throughout my competition career - never lost muscle. Last prep I was trying to lose muscle in order to fit in different category. Combined dnp with tons of cardio - yip that did the trick LOL. didn't really decrease kcal intake cause didn't want that stringy appearance but wanted to hold on to muscle volume. worked well. muscle loss was intentional though.
After taking almost a decade off the juice I hopped back on 100mg anavar and 20mg Superdrol and started taking 250mg DNP along with a 1,000kcal diet of 250g protein and zero fats and carbs. Did as much cardio as I could. Lifted twice per week. I actually gained muscle.