Local anaesthetic-induced myotoxicity in regional anaesthesia: a systematic review and empirical analysis

Recent reports of local-anaesthetic (LA)-induced myotoxicity after peripheral nerve blocks have increased the interest in this less commonly known complication. Basic science evidence investigating LA-induced myotoxicity seems to demonstrate a pattern, but findings from human studies vary. This systematic review summarises the existing myotoxicity evidence and empirically examines its implications. Databases were searched for all in vitro animal and human studies evaluating LA-induced myotoxicity. Studies were stratified by design. Data sought included the model examined, LA used, injury mechanisms, nature of damage, and extent of recovery. For human studies, we also aimed to estimate prevalence and recovery rates. One hundred and fifteen studies, mainly animal and ophthalmic, were included. Myotoxicity risk factors included higher concentrations and prolonged exposure to LA, and use of bupivacaine. Injury mechanisms involved early and late aberrations to cytoplasmic calcium (Ca²⁺) homeostasis by the sarcoplasmic reticulum Ca²⁺ ATPase. Incidence in ophthalmic studies was 0.77% (392 of 50 618). Inflammatory changes within a few days after exposure marked the onset of myotoxicity, and myo-degeneration followed within the first week post-exposure. Time to recovery in human muscles ranged between 4 days to 1 yr. None/partial and complete recovery were observed in 61% and 38% of patients, respectively. Across all experimental models, skeletal muscles exposed to LA consistently display myotoxic effects. Evidence is robust in animal and ophthalmic studies, and displays a concerning signal with continuous adductor canal block use in human case reports. Exploring the clinical prevalence, severity, and risk-reducing strategies of myotoxicity should be prioritised.