Whiplash-induced Thoracic Outlet Syndrome Treated With Botulinum Toxin.

Overview

Whiplash injuries following car accident are common, it has been reported to affect 83% of individuals injured in traffic collisions (Yadla S, 2007). The condition is caused by a rapid acceleration followed immediately by a rapid deceleration of the neck and head. The annual North American incidence rate is estimated to be 600 per 100,000 people (Holm LW, 2008). The condition is costly for society and disabling/painful for the patients. Depending on the collision type, the biomechanics of muscles will be affected differently and consequently the clinical presentation will vary. T-bone type of car collisions (when the front of one vehicle strikes the side of another) may induce thoracic outlet syndrome (TOS) following compression on the nerve and artery bundle by the scalene muscles (lateral stabilizers of the neck). An appropriate and detailed examination of the patient is necessary to identify the cause of the resulting pain and disability. Once a functional thoracic outlet syndrome is identified the proposal is to treat this with botulinum toxin.

TOS symptoms will typical emerge within 24-48 hours following the accident. The duration will depend on the level of severity of the muscle damage. If the severity is a grade 1 (mild damage to individual muscle fibers), symptoms may last up to 3 weeks. If the severity is a grade 2 (more extensive damage with more muscle fibers involved/no complete rupture), symptoms may last up to 3 months. However, in many cases, due to muscle swelling and consequently compression of the nerve plexus, a persistent reflex spasm of muscle develops. A potentially effective treatment strategy, in patients presenting TOS associated clinical symptoms in the proper distribution, is to relax the scalene muscles that surround the nerve plexus. Botulinum toxin, such as incobotulinumtoxinA (XEOMIN, Merz herapeutics), have been shown to be effective and safe in relaxing these muscles in conditions like spasticity, blepharospasm and cervical dystonia (Kanovský P, 2009; Benecke R, 2005; Roggenkämper P, 2005). It is hypothesised that a subtype of whiplash defined as functional TOS could be improved with incobotulinumtoxinA injections into the medial scalene muscle. IncobotulinumtoxinA when injected into the medial scalene is expected to induce muscle relaxation which leads to nerve plexus decompression. The effect is anticipated to last approximately 3 months, which is the duration of effect of botulinum toxins type A. A similar effect can be induced using a local anaesthetic, such xylocaine, since it has a similar mechanism of action, but his effect should be short lived.