What are technical considerations for the use of botulinum toxin (BTX) in pain management?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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Most advocate precise placement of neurotoxin injections into pertinent sites with minimal unwanted diffusion. Areas to avoid include the inferior-lateral frontalis where weakness may cause brow ptosis. Injections into the middle and lower face must be carefully placed and dosed to avoid asymmetry of the mouth or dysphagia. Unwanted diffusion of the neurotoxin behind the orbit causing diplopia or eyelid ptosis is best avoided by performing periorbital injections with the patient sitting, so that the head and neck are vertical.

Following craniofacial and some cervical injections, patients are instructed to remain in a vertical posture and to avoid touching or manipulating the injected areas for as long as 3 hours. Increased headache pain with muscle spasm at the injection sites can occur in about 20% of patients and is maximal during the 2-10 days following treatment. This adverse side effect is often alleviated by manual physiotherapy and/or safely-placed injections of a local anesthetic agent. Refractory symptoms of postprocedure muscle spasm with pain may benefit most from a repeat BTX session with adjunctive physiotherapy.

The desired degree of paresis induced by chemodenervation is determined by the muscle's role in headache production and its function. Most people can compensate for dense paresis of the emotive glabellar and frontalis muscles by the facility of the eyes to express feelings. Conversely, the temporalis and masseter muscles work synergistically to perform mouth closure necessary for mastication. The degree of weakness desired in these muscles is determined by the extent that they influence facial pain or headache. Therefore, BTX dosages must be calculated to maintain masticatory function with sufficient therapeutic dosing to reduce pain.

Furthermore, dosing for pain relief should produce or preserve a balance of strength between the temporalis muscle and its synergistic partner, the masseter. EMG needle guidance to assure correct needle placement into the masseter is useful, but usually unnecessary. The needle is guided into the body of the muscle, specifically into symptomatic spasm or trigger points, by grasping the painful muscle between the thumb externally to the needle insertion site on the skin and then placing the second and third fingers intraorally.

Needle depth and placement into the target area is monitored, and any penetration of the needle intraorally should be readily discovered. BTX should never be injected until the needle has reached the intended target site and the operator is confident that placement is correct. If the needle enters the oral cavity BTX injection should be aborted. The needle must be withdrawn and placed through a new site, with EMG guidance if necessary, into a site that will not allow BTX diffusion through a prior mucosal puncture site. A safer approach would entail delaying the procedure for 6-8 weeks, if the patient did not experience any adverse effects, such as hoarseness or dysphagia. BTX injected into the oral cavity, especially if swallowed, may cause a serious, potentially lethal, paresis of pharyngeal musculature.

The upper cervical and occipital muscles, especially the occipitalis, splenius capitis and cervical paraspinal muscles, may cause headache and trigger migraine. Often, these muscles contribute to pain and headache by irritation of the adjacent greater occipital nerve, causing concomitant neuropathic pain or symptoms of neuralgia. Frequently, the trapezius or symptomatic parathoracic muscles can trigger headache. Injections into this region may induce unwanted weakness of the supraspinatus and infraspinatus muscles, which form part of the rotator cuff, causing the humeral head to rise. Injection of trapezius and levator scapulae muscles may cause the acromion to shift anteriorly and sag inferiorly. This can result in a painful shoulder impingement syndrome, which usually manifests 7-10 days following BTX treatment.

Onset of a BTXA clinical effect usually occurs at 7-10 days and plateaus at 3 weeks. The neuromuscular blocking action of BTX-A lasts 3-4 months; however, the duration of reduced pain can be substantially longer, and a mitigation effect more specific for migraine may continue to develop beyond 2-3 months after the injection session. Headache improvement can be identified through the use of a diary and other self-reporting measures. Other salient measures include reduction of oral prophylactic medications, improved response from abortive therapies, as well as reduced frequency, intensity and severity of headache symptoms.

However, to conduct a large multicenter study, rules that governed injection technique and dosing were necessary to adopt to give the study a reasonable opportunity of using successful injectors, thereby providing the best chance for a successful outcome. Patients were recruited if they satisfied the definition of chronic migraine.

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