My 4 year old son has a PWS on his right arm, right back, the top of his chest and some spots on his right leg. Agree that this seems to be much rarer than facial PWS. Perhaps easier to live with also.
His arm and hand are bigger than the non-PWS side... but this has caused no physical discomfort or difficulties, he is definately right handed and has full mobility. The first dermo we saw even suggested (jokingly) that he should take up tennis or golf as he would probably have a stronger right arm than others!
I tossed up on getting laser treatment for him for over a year. My first impulse was to go for it, mainly due to the teasing factor and the risks of cobbling later on. But then I read posts here and elsewhere about kids living with PWS - and generally they were positive about it... after all everyone gets teased at school, big bum, big nose, red hair, etc...
We consulted with specialists in two different towns, both said that treatment was neither necessary nor urgent - and that breakthroughs are being made in the technology, so perhaps it would be better to wait. They also said that treatment hurts - and that if my son was not concerned about his birthmark and did not ask for treatment, why put him through the suffering?
Finally we decided not to do anything, but to revisit that decision when he gets older - perhaps when he is 8. If teasing is getting out of hand at that point, or if he ever asks for treatment, then we will do something about it.
He is a happy well adjusted boy - I have witnessed him more than once explaining his "red hand" to other kids, and it causes him no trauma or embarassment, indeed it seems to help him break the ice in making friends! He never complains of pain or tries to hide it. For the moment at least, I think we have made the right decision in holding off on treatment.