Patients randomized to ustekinumab (10 with PPPP and 10 with PPP) will receive ustekinumab at Day 0, Weeks 4 and 16 and placebo at Week 20 whereas patients randomized to placebo (10 with PPPP and 10 with PPP) will receive placebo at Weeks 0 and 4 and ustekinumab at Weeks 16 and 20.