I'm on the fence with this one. Really, any time you start running any steroid, no matter how mild or strong, it is going to begin shutting down your natural production of test from day one. I have seen people do small cycles of anavar or dbol, not using test, and they make it through ok. It's going to be an individual thing. Some people are going to suffer more than others from shut down. Plus, the effect of anavar alone isn't going to give you that large of a muscle gain. There are only a couple types of people I would suggest an anavar only cycle to. 1, an athlete that wants to improve strength in a sport, or 2, to a younger person, say under 22, that foolishly thinks that steroids are going to be their "short cut". For athletes, even 20mg is enough to improve performance. For the younger person, there is a possiblity that steroids converting to estrogen can prematurely close growth plates and anavar does not convert. 

As you may have figured out from the first part of the answer, yes, you need to do PCT. As I said above, any stroid will shut you down. This includes pro hormones