Twenty patients with active Palmo-Plantar Pustular Psoriasis (cohort A) and twenty patients with active Palmo-Plantar Pustulosis (cohort B) will be included in this placebo-controlled double-blind study.Patients in each cohort will be randomized (1:1) to receive either ustekinumab S/C (Sub-Cutaneous) (45 mg for patients weighting 100 kg or less, and 90 mg for patients weighting more than 100 kg) or placebo.