Psoriatic arthritis is a long-term inflammatory arthritis that occurs in people affected by the psoriasis. The classic look of psoriatic arthritis is swelling of entire toes or fingers with a sausage-looking appearance. It can happen in association with small depressions in the nail (pitting), thickening of the nails, and detachment of the nail from the nailbed. Genetics are thought to be strongly involved in the development of psoriatic arthritis. Obesity and certain forms of psoriasis are thought to increase the risk. Topical treatments cannot be used for psoriatic arthritis.