They studied 43 people with moderate, long-lasting shoulder pain caused by osteoarthritis.
The patients had already tried other drug treatments for their chronic shoulder pain and weren't candidates for shoulder surgery. They got one injection to their painful shoulder joint.
For half of the patients, the shot included Botox and the pain drug lidocaine. For the other patients, the shot contained salt water and lidocaine.
About a month later, the patients rated their shoulder pain. Those who had gotten Botox and lidocaine reported less pain than those who had gotten salt water and lidocaine.
"These findings are very promising," write the researchers, who included Jasvinder Singh, MBBS, MPH, of the Minneapolis VA Medical Center, University of Minnesota, and Mayo Clinic School of Medicine.
Why would Botox ease shoulder pain? Botox contains a tiny dose of botulinum toxin type A, which may curb certain chemicals involved in joint pain, the researchers suggest.
Singh presented the study today in Boston at the American College of Rheumatology's annual scientific meeting.
Singh reports receiving travel grants from Allergan, the company that makes Botox.