The condition and the treatment
Psoriatic arthritis is caused by inflammation, which results in painful, swollen or stiff joints. It usually develops in people who already have the skin condition psoriasis and is described as 'active' when the skin or joint symptoms occur.
Ustekinumab (Stelara) changes the body's inflammatory response to reduce the symptoms of psoriatic arthritis.
NHS Choices (www.nhs.uk) may be a good place to find out more.