Obviously sprinting will produce muscle growth in the legs, but will sprinting increase muscle mass in upper body (even if it is a slight gain). Sprinting will defintley not lead to muscle atrophy like long distance running right?
If you have not been sprinting before you will gain muscle mass in your legs and hips (glutes, abductors, flexors and external rotators). This is true even if you have been doing a lot of weight training for your lower body. Most people who take up sprinting comment that they notice an addition of muscle mass in the area where the hamstrings meet the butt (upper biceps femoris).
As for your upper body, you will get a stronger core (abs and back), but this does not translate into any significant addition of muscle mass that will really stand out.
The reason sprinters (100 and 200m) have a lot of muscle is because they spend a lot of time doing weights. They didn't add this muscle mass on the track. So don't count on sprinting adding a lot of upper body muscle.
The short answer is that sprinting does not lead to muscle atrophy in the same way as long distance running does. This said, no matter what you do, if you burn more calories than you consume you will shrink.
The most important thing for you to remember if you start sprinting is to warm up properly. It is very easy to injure yourself when sprinting (hams and hip flexors are most common). Google for proper sprinting warm-ups and be very careful. Always remind yourself to run relaxed, and be careful with practicing starts in the beginning.
I would not do more than two sessions a week in the beginning.