Over the last several years, botulinum toxin type A (BTX-A) has been increasingly used in the treatment of various medical conditions. Increasing literature supports the role of BTX-A in the treatment of chronic pain syndromes. Blockade of acetylcholine release from the presynaptic membrane plays an important role in relief of muscles spasms and myofascial pain syndromes. However, some animal models suggest alternative mechanisms for the analgesic
effects of this agent. Some of these mechanisms include action against locally accumulated stimulant neurotransmitters (glutamate, substance P) also pertain to the pathophysiology of plantar fasciitis. This author and colleagues recently published a randomized, placebo-controlled, prospective, short-term clinical trial that studied the effect of BTX-A injection for refractory plantar fasciitis.
The patients with plantar fasciitis had almost all of the aforementioned therapeutic measures with the exception of extracorporeal shock or surgery. The solution of BTX-A (Botox®, Allergan, Inc.) was prepared by mixing 100 U with 1 cc bacteriostatic normal saline. We injected the patients of group A with 70 U BTX-A (0.7 cc) in two divided doses: 40 U (0.4 cc) in the tender region of the heel medial to the base of the plantar fascia insertion and 30 U (0.3 cc) in the most tender point of the arch of the foot (between an inch anterior to the heel to middle of the foot; see Fig. 1). A 27-gage, 0.75-inch needle was used for injections. Group B received normal saline at the same locations and with similar volume. In patients with bilateral plantar fasciitis of comparable severity, BTX-A was injected in one foot and saline in the other foot. All patients were also given a handout reviewing a home stretching program targeting the plantar fascia and gastroc/soleus muscle complex. No medication changes were recommended; however, patients were informed that receiving another injection or surgery on their foot would terminate their participation in the study.
Main outcome measures included pain visual analog scale, Maryland foot score, pain relief visual analog scale, and pressure algometry response. Patients were assessed prior to injection, at 3 weeks and at 8 weeks. The study revealed statistically significant changes in the
treatment group. Compared with placebo injections, the BTX-A group improved in all measures: pain visual analog scale (p < 0.005), Maryland foot score (p = 0.001), pain relief visual analog scale (p < 0.0005), and pressure algometry response (p = 0.003). No side effects were noted.
The work from animal and human data demonstrates that BTX-A can affect each of the aforementioned mechanisms:
1. Both clinical and experimental data have shown that the introduction of BTX-A into a muscle results in transient loss of muscle volume via induction of muscle atrophy. Considering our injection methodology, it is possible that the subsequent reduction of the size of the intrinsic foot muscles resulted in the relief of pressure on the neurovascular structures trapped under a tight and enlarged plantar fascia.
2. BTX-A has been shown to inhibit the release of substance P from dorsal root ganglia as well as block the release of glutamate from synaptosomes (14,15).
3. Pretreatment with BTX-A in rats results in a decreased local inflammatory response after the administration of formalin (16).
4. Intramuscular injection of BTX-A reduces the discharge of intrafusal muscle fibers, which normally convey large non-nociceptive input (reporting muscle length) to the spinal cord (5). In chronic pain conditions (which may be the case in our subjects who all complained of symptoms for >6 months), reduction of this input theoretically can reduce the level of central sensitization. In animals, administration of BTX-A reduces the discharge of sympathetic neurons (17) and thus can reduce the role of the sympathetic system in pain maintenance.
Our injection technique aimed to treat both the plantar fascia and the underlying muscles in case that both fascia and muscle contributed to the patients' pain. In the fascia, we hoped BTX-A to reduce inflammation and in the underlining muscles we hoped to see a positive effect on heel pain via muscle relaxation and loss of muscle volume. Yet other suggested BTX-A actions (decreased central sensitization, decreased sympathetic activity, and reduced accumulation of substance P and glutamate) could have worked at the level of both structures. In our clinical practice, BTX-A injection into the arch of the foot with a 27-gage, 0.75-in. needle often relieves painful flexor toe spasms in patients with stroke, head injury, cerebral palsy and multiple sclerosis. We chose to treat preferentially the tender points in our patients because previous reports in myofascial pain syndromes have linked success in pain relief to this approach (18,19).
Although most of our responders revisited us at 6 months, only a few could be followed for 12 months because of the moving nature of our studied population (mostly young military soldiers) and the fact that the study was conducted at the time of a major military mobilization (2002-2004). Those who visited at 6 months and a few who were seen at 12 months had no recurrence of symptoms. Several subjects were able to return to full duty as military police, or return to activities such as bowling, tennis, and running. One patient was able to mow the lawn after an inability to perform this chore for 10 years. A few subjects with bilateral plantar fasciitis requested that their placebo foot be injected with BTX-A. They also had similar results. These limited long-term results are encouraging but need to be reproduced in a prospective study of a larger number of patients.
The results of our study demonstrate that the injection of BTX-A into the plantar region significantly improves the pain of recalcitrant plantar fasciitis at both 3 and 8 weeks after treatment. Although the exact mechanism of action has yet to be elucidated, several theories presented may explain the positive effect. Furthermore, blinded studies are necessary to confirm these results, which bear significant implications in caring for patients suffering from this disorder. Long-term prospective studies are also necessary to show if these positive effects can be sustained with repeated treatments. According to the American Society for
Aesthetic Plastic Surgery, the average cost of BTX-A injection ranges from $300 to $500. Compared with ECSWT, which may require multiple sessions, BTX-A injection for plantar fasciitis is, for the most part, a one-time procedure. Treatment of plantar faciitis with BTX-A should be considered for those patients who have failed standard modes of treatment.
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