Base-of-thumb osteoarthritis is a common condition affecting middle-age persons. Base-of-thumb osteoarthritis induces pain and hand-specific limitations in activities. For short and midterm effects, therapeutic options usually include splinting, exercise therapy and intra-articular injections of glucocorticoids or hyaluronic acid. However, evidence of efficacy of intra-articular therapies in base-of-thumb osteoarthritis and international guidelines are inconsistent. Recently, the use of intra-articular botulinum toxin A as a pain killer has raised intense interest. The exact mechanisms of pain modulation by botulinum toxin A in osteoarthritis are unclear. It has been suggested that botulinum toxin A could directly reduce peripheral sensitization and indirectly reduce central sensitization. Indeed, recent studies suggest an inhibitory role of botulinum toxin A on the release of mediators involved in nociception, such as P substance, calcitonin gene-related peptide and glutamate. Open and randomized controlled trials of botulinum toxin A in knee osteoarthritis support short to mid-term positive clinical effects on pain. However, no study has reported results for base-of-thumb osteoarthritis