Botulinum Neurotoxin Injection as a Therapeutic Option in Thoracic Outlet Syndrome Caused by a Supernumerary Scalenus Muscle: A Case Report

Thoracic Outlet Syndrome (TOS) is a neurovascular syndrome and may occur as a result of compression of brachial plexus elements and/or subclavian vessels as they traverse the cervicoaxillary canal. One of the causes of TOS is the existence of a supernumerary scalene muscle, usually denominated as scalenus minimus. Botulinum Toxin Type A (BoNT-A) acts by binding presynaptically to high-affinity recognition sites on the cholinergic nerve terminals and decreases the release of acetylcholine, suppressing muscle overactivity. BoNT-A reduces contraction in injected muscles, causing focal chemodenervation and has been described as a non surgical effective treatment in selected cases of TOS. Here, is the case of a 44-year-old woman diagnosed with refractory TOS, who presented with paresthesia in the fourth and fifth fingers of her right hand, associated with a feeling of lack of coordination in the same hand. On Magnetic Resonance Imaging (MRI), a supernumerary scalene muscle was identified as a probable cause of TOS. She was treated with chemodenervation of the scalenus anterior muscle (30 Units) and scalenus medius muscle (30 Units), using incobotulinumtoxin A. The patient had a very significant clinical improvement after Anterior Scalene (AS) and Middle Scalene (MS) muscle BoNT-A injections. Incobotulinumtoxin A neurotoxin injection is a therapeutic option in TOS.