How effective is ustekinumab in controlling psoriatic arthritis?

Recently ustekinumab has been approved for the therapy of psoriatic arthritis (PsA). Some case series have been published reporting new onset of inflammatory arthritis in psoriasis patients treated with ustekinumab. In addition, flare of joint inflammation in PsA patients has also been reported. We describe a case series of seven patients affected by PsA who experienced either a worsening or a flare of inflammatory arthritis during treatment with ustekinumab.