(Adds detail)

April 20 (Reuters) - Eli Lilly and Co said its experimental drug, ixekizumab, reduced the signs and symptoms of active psoriatic arthritis in patients more than a placebo did in a late-stage trial.

Up to 30 percent of psoriasis patients develop psoriatic arthritis, an inflammatory form of arthritis that can cause swelling, stiffness and pain in and around joints, according to the National Psoriasis Foundation.

The study, which tested two doses of ixekizumab against a placebo for 24 weeks, showed that Lilly's drug was statistically superior, as demonstrated by the proportion of patients achieving an ACR 20 response.

ACR 20 is a standard assessment defined by the American College of Rheumatology as one that reduces the signs and symptoms of a disease by 20 percent.

The psoriatic arthritis patients in the trial were required to have had a flare up of symptoms in at least the past six months as well as be untreated by certain drugs.

Ixekizumab, a monoclonal antibody, is injected under the skin and is also being tested to treat plaque psoriasis.

Last August, Lilly announced data that showed ixekizumab was successful in multiple late-stage studies in patients with moderate-to-severe plaque psoriasis.

Lilly shares closed at $72.47 on Friday on the New York Stock Exchange.

(Reporting by Natalie Grover in Bengaluru; Editing by Savio D'Souza)