Paradoxical Pustular Psoriasis Following Treatment of Chronic Plaque Psoriasis with Ustekinumab

A 51-year-old female with red plaques and scales for 20 years, aggravated with pustules for more than 10 days.Physical examination: scattered red patches, silver-white scales, thin film, Auspitz sign (+) can be seen on the head and face.The trunk and limbs were scattered in large erythema and erythema, on which were dense pustules of the size of chestnut. The central color of local pustules was brown, presenting target-shaped lesions, and some pustules fused into pus lake.Vulvar mucosa scattered in pustules, erosion surface.Nail clipping thimble changes, deck thickening changes.Histopathology: Hyperkeratosis, fusion keratosis, thinning or disappearance of granular layer, epidermal psoriatic hyperplasia, munro and Kogoj microabscess, dermal papilloma, vascular dilatation, perivascular lymphocyte infiltration.Diagnosis: pustular psoriasis.