Botulinum toxin injections for shoulder and upper limb pain: a narrative review.

Botulinum toxin (BoNT) has been widely employed to treat poststroke spasticity, cervical dystonia and muscle hyperactivity. Recently, BoNT injections are increasingly used in treating musculoskeletal pain. The mechanism of BoNT in pain relief comprises relaxation of overused muscles and inhibition of inflammatory nociceptive cytokines/neurotransmitters. As BoNT injections seem promising in treating painful musculoskeletal disorders, we aimed to investigate its effectiveness in shoulder and upper limb pain. Although the present article is a narrative review, we employed a systematic approach to search for relevant articles in PubMed. A total of 19 clinical studies were included. Here, we observed that intramuscular BoNT injections were helpful in stroke patients with hemiplegic shoulder pain. In shoulder joint pain, intra-articular and intrabursal BoNT injections achieved a longer period of pain relief than corticosteroid injections. Similarly, a more durable effect of intramuscular BoNT than saline injections was seen in shoulder myofascial pain. Its use in complex regional pain syndrome and persistent upper limb pain in breast cancer survivors was insufficient, necessitating more studies. Since not all of the included studies could provide Class I of evidence based on the efficacy criteria used by American Academy of Neurology, controlled clinical trials in a larger number of patients are necessary to verify validity of these findings in the future.