Presynaptic effects of botulinum toxin type A on the neuronally evoked response of albino and pigmented rabbit iris sphincter and dilator muscles

Botulinum toxin: mechanisms of action

This review describes therapeutically relevant mechanisms of action of botulinum toxin (BT). BT's molecular mode of action includes extracellular binding to glycoproteine structures on cholinergic nerve terminals and intracellular blockade of the acetylcholine secretion. BT affects the spinal stretch reflex by blockade of intrafusal muscle fibres with consecutive reduction of Ia/II afferent signals and muscle tone without affecting muscle strength (reflex inhibition). This mechanism allows for antidystonic effects not only caused by target muscle paresis. BT also blocks efferent autonomic fibres to smooth muscles and to exocrine glands. Direct central nervous system effects are not observed, since BT does not cross the blood-brain-barrier and since it is inactivated during its retrograde axonal transport. Indirect central nervous system effects include reflex inhibition, normalisation of reciprocal inhibition, intracortical inhibition and somatosensory evoked potentials. Reduction of formalin-induced pain suggests direct analgesic BT effects possibly mediated through blockade of substance P, glutamate and calcitonin gene related peptide.

Injections of botulinum toxin type a produce pain alleviation in intractable trigeminal neuralgia

To report the effects of local injections of botulinum toxin type A regarding pain relief and long-term control in a patient with intractable trigeminal neuralgia. The patient was a 75-year-old man with trigeminal neuralgia in the left hemifacial region. His pain was unbearable and could not be controlled by carbamazepine, amitriptyline, or blocked by infiltration of a glycerol solution or phenol. The authors evaluated pain intensity, quality, and location using a Visual Analog Scale to establish the efficacy of botulinum toxin type A injections. Two units of botulinum toxin type A (Botox) were subcutaneously injected once in eight points distributed along the territory of V1 and V2. Visual Analog Scores were measured at baseline and at 7, 30, 60, and 90 days after treatment. The authors also examined the patient's general condition and daily life activities. The Visual Analog values were, respectively, 82, 54, 25, 25, and 45 mm at each follow-up examination. No side effects were observed on the site of injection and on the patient's clinical state. The authors have been able to reduce trigeminal neuralgia pain with botulinum toxin type A injections in the V1, V2 territory during all the period of study, as well as to withdraw all medication. Interestingly, there was concomitant reduction of pain also in V3, which was not injected.

Botulinum toxin: mechanisms of action

Botulinum toxin (BT) has been perceived as a lethal threat for many centuries. In the early 1980s, this perception completely changed when BT's therapeutic potential suddenly became apparent. We wish to give an overview over BT's mechanisms of action relevant for understanding its therapeutic use. BT's molecular mode of action includes extracellular binding to glycoprotein structures on cholinergic nerve terminals and intracellular blockade of the acetylcholine secretion. BT affects the spinal stretch reflex by blockade of intrafusal muscle fibres with consecutive reduction of Ia/II afferent signals and muscle tone without affecting muscle strength (reflex inhibition). This mechanism allows for antidystonic effects not only caused by target muscle paresis. BT also blocks efferent autonomic fibres to smooth muscles and to exocrine glands. Direct central nervous system effects are not observed, since BT does not cross the blood-brain barrier and since it is inactivated during its retrograde axonal transport. Indirect central nervous system effects include reflex inhibition, normalisation of reciprocal inhibition, intracortical inhibition and somatosensory evoked potentials. Reduction of formalin-induced pain suggests direct analgesic BT effects possibly mediated by blockade of substance P, glutamate and calcitonin gene-related peptide.

Mechanism of Action of Botulinum Toxin Type A in Migraine Prevention: A Pilot Study

OBJECTIVE

The main objective of this study is to determine whether change in migraine frequency is correlated with a denervation pattern of the corrugator muscle after local botulinum toxin type A injections.

BACKGROUND

Recent studies suggest botulinum toxin type A is effective in preventing migraine. Relaxation of the corrugator muscle may be one of multiple targets of botulinum toxin type A in relieving migraine pain.

METHODS

The pretreatment amplitude of the compound muscle action potential (CMAP) was obtained in 10 patients with a migraine frequency of two to six attacks per month following stimulation of the temporal branch of the facial nerve. Patients were subsequently injected with 20 units of botulinum toxin type A at predefined sites in the procerus and corrugator muscles. CMAP was obtained on days 7, 30, 60, and 90 after injection. Migraine frequency, as reported in headache diaries, was compared with the amplitudes obtained.

RESULTS

A 50% decrease in CMAP was demonstrated in the total group by day 7. Maximal decline of CMAP was observed by day 30, and was sustained at day 60. Migraine frequency declined by 50% or more in 7 of 10 patients by day 60. Migraine response to botulinum toxin type A treatment did not correlate with the denervation pattern.

CONCLUSION

Relaxation of the corrugator muscles is not solely responsible for the pain relief in migraine patients treated with botulinum toxin type A.

Botulinum toxin and other new approaches to migraine therapy

The number of migraine treatments and our understanding of migraine pathophysiology are both increasing. Newer treatments focus on migraine prevention. Botulinum toxin (BTX) is a potent neurotoxin used primarily to treat diseases associated with increased muscle activity. Recently, BTX was found to have antinociceptive effects that are probably independent of its muscle-relaxant action. Clinical trials support the efficacy of BTX type A (and possibly also type B) in the treatment of migraine. The anticonvulsant topiramate was recently shown to be effective for migraine prevention. At the low doses used for this indication, cognitive side effects are not a major concern. Another new approach to migraine prevention is angiotensin type 1 (AT1) receptor blockade. The high tolerability of the AT1 receptor blocker candesartan warrants further studies to assess its role in migraine prevention.

The Therapeutic Potential of Botulinum Toxin

BACKGROUND

Botulinum toxin type A (BTX-A; commercial preparation BOTOX) is most well known for its effect on muscle contraction because of the BTX binding to the presynaptic nerve terminal, inhibiting the release of acetylcholine (ACH). The therapeutic benefit of BTX-A, however, can also be isolated to pain relief alone, suggesting that BTX-A also works through additional modes of action.

OBJECTIVE

This article provides insight by an experienced physician into four different case reports. Each case demonstrates the therapeutic potential of BTX-A and the possibility of a different mechanism of action for BTX other than the inhibition of ACH release.

RESULTS

Four patients, each with different symptoms such as relapsing-remitting multiple sclerosis, postherpetic neuralgia, peripheral neuropathy, and severe tingling caused by herniation of cervical vertebrae at the level of C8, were treated with BOTOX, and their symptoms were alleviated.

CONCLUSIONS

The BTX-A mechanism providing pain relief is hypothesized to be something other than muscle relaxation by inhibiting the release of ACH at the neuromuscular juncture, such as inhibition of the release of substance P or the blocking of autonomic pathways, etc. This article is intended to continue to keep physicians using this substance for dermatologic indications aware of the potential unsuspected effects.

A preliminary comparison of the efficacy and tolerability of botulinum toxin serotypes A and B in the treatment of myofascial pain syndrome: a retrospective, open-label chart review

BACKGROUND

Myofascial pain syndrome (MPS) is characterized by acute or chronic regional muscle pain associated with single or multiple trigger points within taut bands of muscle. Botulinum toxins have clinical utility when sustained focal muscle relaxation is required and may be a useful addition to the treatment armamentarium for MPS.

OBJECTIVE

The purpose of the present article was to compare the efficacy and tolerability of botulinum toxin serotypes A and B (BTX-A and BTX-B) in the treatment of MPS.

METHODS

This was a retrospective, open-label, single-center chart review. Charts of all patients who received either BTX-A or BTX-B for MPS between January and November 2001 were included in the review. Patients rated the intensity of their pain on a visual analog scale (VAS) from 0 = no pain to 10 = worst pain imaginable before and after receiving BTX-A or BTX-B.

RESULTS

The charts of 91 patients (74.7% female, 25.3% male; mean [SD] age, 47 [10.2] years) who received BTX-A (n = 56; mean dose, 256.9 U; range, 100-600 U) or BTX-B (n = 35; mean dose, 9000 U; range, 2500-20,000 U) were included in this retrospective review. Patients who received BTX-A had significantly greater mean reductions in VAS pain scores compared with those who received BTX-B (mean reduction, 2.7 vs 1.8, respectively; P < 0.001). Patients who received BTX-A also reported significantly longer durations of pain relief compared with those who received BTX-B (4.5 vs 2.7) months; P < 0.001). Eight of 56 patients (14.3%) in the group that received BTX-A reported mild adverse events that included flulike symptoms, injection-site pain, and weakness of the neck muscles. Seven of 35 patients (20.0%) in the group that received BTX-B reported adverse events that included mild flulike symptoms, dry eyes, severe visual disturbances, and severe dry mouth.

CONCLUSION

Patients with MPS who received BTX-A reported significantly greater reductions in pain for longer durations compared with those who received BTX-B. No patients who received BTX-A experienced severe systemic adverse events, compared with 4 patients who received BTX-B. The results of this comparison are consistent with the US Food and Drug Administration-approved labeling indicating that BTX-A is not interchangeable with any other botulinum toxin in terms of biological activity.

Botulinum toxin type A for the treatment of chronic neck pain after neck dissection

BACKGROUND

Neck dissection surgery is often followed by chronic head and neck pain. To date optimal treatment of this type of pain is lacking. Botulinum toxin type A (BTX-A) has been shown to be effective in the treatment of myofascial pain syndrome and headache. In a pilot study, we wanted to test the effectiveness of BTX-A for the treatment of chronic neck pain after neck dissection.

METHODS

Sixteen patients with chronic neck pain after neck dissection were included in this prospective, open study. Eighty to 320 units of BTX-A (Dysport) were injected into muscular trigger points. Outcome measures included chronic pain and shooting pain on the basis of visual analog scales and quality of life improvement (EORTC QLQ-C-30; EORTC QLQ-H and N35) before and 4 weeks after treatment.

RESULTS

Patients showed a significant reduction in chronic pain (4.5 before to 3.3 after treatment, p =,005) and in shooting pain (6.1 before to 4.7 after treatment, p =.005). There was a trend toward improvement in global quality of life (QLQ-C30, p =.097) and an increase on the functional scale "pain" (QLQ-H and N35, p =.071).

CONCLUSIONS

BTX-A treatment of subjects with chronic neck pain after neck dissection resulted in a fast and significant reduction of pain. A significant improvement in quality of life may be expected in a longer time course after treatment.

Migraine: an ophthalmologist's perspective

PURPOSE OF REVIEW

Migraine is a common disorder with visual and neurologic manifestations. Many patients present to ophthalmologists without a previous diagnosis of migraine. It is therefore essential for the ophthalmologist to have a good understanding of migraine to appropriately help these patients. Neurologic syndromes with migraine and retinopathy are well known. Here again, the ophthalmologist may play a role in establishing the correct diagnosis.

RECENT FINDINGS

For long the initial changes during a migraine attack have been shown to occur in the occipital cortex. In the recent years, the understanding of migraine has advanced with the availability of functional neuroimaging. A possible role of brainstem structures in the initiation of migraine attacks has been proposed based on functional magnetic resonance imaging blood oxygenation level-dependent signals. Activation of brainstem structures preceded activation of occipital cortex. Our understanding of cortical spreading depression is also advancing. Using multiwavelength optical intrinsic imaging, cortical spreading depression has been shown to have a triphasic response in rats. For the first time it has been shown that the cortical spreading depression activated the trigeminovascular system, which is followed by a series of cortical meningeal and brainstem events that cause the migraine headache. Sildenafil has been shown to induce migraine attack without dilation of cerebral blood vessels, further confirming that Wolf's vasogenic theory may not be true. Several loci for migraine have been identified in recent years. A new locus for migraine with and without aura has been identified on chromosome 6, a locus for migraine without aura to chromosome 14, and a locus for migraine with aura on chromosome 4.

SUMMARY

Our understanding of migraine is rapidly evolving with functional neuroimaging. There are several unanswered questions. In this article, we will review the epidemiology, genetics, and clinical features of various forms of migraine with emphasis on ocular migraine, pathogenesis, and briefly the management of migraine.

Botulinum toxins in pain management

BTs are a useful treatment in refractory MPS and have shown promise in various superficial neuropathic pain syndromes. Presumably BTs work by breaking the spasm/pain cycle, giving the patient a "window of opportunity" for traditional conservative measures to have a greater beneficial impact, but several studies suggest that a direct antinociceptive effect distinct from any reduction in muscle spasm may be at play. The major benefit of BTs compared with standard therapies is duration of response. BTs cannot be considered a "first line" treatment for any pain application; however, in refractory cases in which nothing else has helped, BTs may offer the patient and physician a chance for improvement and perhaps even cure.

Botulinum toxin type A as an effective prophylactic treatment in primary headache disorders

OBJECTIVE

To measure the effect of botulinum toxin type A (Botox, Allergan, Inc, Irvine, CA) treatment in 271 patients diagnosed with headache in accordance with International Headache Society (IHS) criteria.

BACKGROUND

Botulinum toxin type A has shown promise for the treatment of headache in several clinical trials, but uncertainty remains as to how botulinum toxin type A optimally should be used for treating headache and which patients are best suited for this treatment.

METHODS

This was a retrospective chart review of all patients who received botulinum toxin type A for the treatment of headache from January 1999 to February 2002. Patients were injected with an average dose of 63.2 U (SD, 14.5) of botulinum toxin type A on 2 or more visits, with treatments involving a "fixed-site" or a "follow-the-pain" (or a combination of both) approach. In the fixed-site approach, botulinum toxin type A was injected into the procerus, corrugator, frontalis, and temporalis muscles. In the follow-the-pain approach, botulinum toxin type A was injected into a combination of the procerus, corrugator, frontalis, temporalis, occipitalis, trapezius, and/or semispinalis capitis muscles. The primary outcomes for the trial were the reduction in headache days per month or headache intensity (0 to 3 scale) (or both) from baseline. Patients were diagnosed according to IHS criteria and subsequently classified into the following categories: chronic daily headache (more than 15 headache days per month), episodic tension-type headache, episodic migraine, and "mixed" HA (less than 15 headache days per month, combination of migraine and tension-type headache).

RESULTS

Treatment period was an average of 8.6 months (SD, 6.4); patients received an average of 3.4 doses (SD, 1.6) 3 months apart. Of the 271 patients, 29 (10.7%) had episodic migraine, 17 (6.3%) had episodic tension-type headache, 71 (26.2%) had mixed headache, and 154 (56.8%) had chronic daily headache. Two-hundred fifty-six patients had data for the number of headache days per month, 117 had data for headache intensity, and all 271 had data for headache days or headache intensity. Botulinum toxin type A treatment significantly reduced the number of headache days per month from 18.9 (SD, 10.3) to 8.3 (SD, 8.9) (n=256, P<.001)--a 56% reduction. Headache intensity decreased from 2.4 points (SD, 0.6) to 1.8 points (SD, 0.8) (n=117, P<.001)--a 25% reduction. Of 263 patients surveyed, 225 (85.6%) reported improvement in headache frequency and intensity. There was no correlation of effect/lack of effect with reason for treatment, duration/number of treatments, injection technique, mean/total dose, age, gender, or comorbidity. Approximately 95% of patients did not experience medication side effects.

CONCLUSION

These results suggest that botulinum toxin type A may be an effective and safe prophylactic treatment for a variety of moderate to severe chronic headache types.

Preventative treatment for migraine and tension-type headaches : do drugs having effects on muscle spasm and tone have a role?

Baclofen, tizanidine and botulinum toxin A, agents used to treat disorders of muscle tone, have been studied as potential preventative treatments for migraine, tension-type headache and other related disorders. The most extensive work has been completed with botulinum toxin A. However, there is still a paucity of well controlled, clinical trials with this agent, and overall there have been conflicting and oftentimes equivocal results: studies of its use in migraine headache have suggested efficacy, whereas those of tension-type headache have not shown significant evidence of efficacy. There were few significant adverse events associated with the use of botulinum toxin A in these trials. The mechanism by which botulinum toxin A may work to prevent headache is not clear. Although changes in muscle tone may play a role in the effect of the drug, central mechanisms such as effects on neuropeptides involved in the pathogenesis of migraine may also be relevant. Further clinical trial work is in progress to help determine optimal administration schedules and choice of injection locations with botulinum toxin A for specific headache disorders. There has been limited study of the use of baclofen, an agent that acts centrally via GABA(A) receptors, in migraine and cluster headache, with only two open trials conducted to date. Both of these studies support the use of baclofen in the preventive treatment of headache.Tizanidine, which may have both a peripheral and a central mechanism in the locus ceruleus in migraine headache, has been studied in several clinical trials. Although the primary mechanism of action of this agent is, like clonidine, as an alpha-adrenoceptor agonist, it has little antihypertensive effect. Open trials of tizanidine have shown it to be useful in chronic headache. One well controlled trial, conducted as a follow-up to an open-label trial in the preventive treatment of chronic daily headache, reported tizanidine as having a statistically significant benefit over placebo. Also of interest is its use in conjunction with a long-acting NSAID to aid in the treatment of rebound headache accompanying the discontinuation of overused acute migraine therapies. In conclusion, though limited, the studies suggest the efficacy of botulinum toxin A, baclofen and tizanidine in primary headache disorders.

[Botulinum toxin in headache]

Use of botulinum toxin in headache is a recent method. More and more studies are dedicated to this method. However, despite the large number of published studies, results are contradictory. It is actually difficult to conclude that this therapy is effective or not due to the disparity of clinical studies. Nevertheless, some results are encouraging and studies with a large number of patients have to be done. Here, we take stock about pathophysiological data on the effect of botulinum toxin on pain. Then, we'll report a review of clinical studies available on literature.

Type A botulinum toxin in the treatment of chronic facial pain associated with masticatory hyperactivity

PURPOSE

Chronic hyperactivity of the masticatory muscles is a common functional disorder associated with chronic facial pain and headache. The positive therapeutic effect of botulinum toxin type A on functional disorders and pain symptoms has been known in connection with the treatment of cervical dystonia. The purpose of this report is to assess whether the targeted reduction of masticatory muscular hyperactivity by local injection treatment with botulinum toxin type A can improve facial pain headache symptoms in the event that other treatment methods prove ineffective.

MATERIALS AND METHODS

In an randomized blinded placebo-controlled study, 90 patients (60 verum and 30 placebo) with chronic facial pain were treated with botulinum toxin type A (Botox; Allergan, Ettlingen, Germany) injections into masticatory muscles.

RESULTS

Ninety-one percent of patients who received botulinum toxin improved by a significant mean reduction of approximately 3.2 on a visual analog pain scale. By comparison with t test and chi(2) test, there was a significant difference compared with the placebo group (P <.01).

CONCLUSIONS

The local injection of botulinum toxin type A constitutes an innovative and adequately efficient treatment method for chronic facial pain associated with hyperactivity of the masticatory muscles. An improvement in the painful symptoms can be expected in up to 90% of patients who do not respond to conservative treatment methods.

Evidence for antinociceptive activity of botulinum toxin type A in pain management

The neurotoxin, botulinum toxin type A, has been used successfully, in some patients, as an analgesic for myofascial pain syndromes, migraine, and other headache types. The toxin inhibits the release of the neurotransmitter, acetylcholine, at the neuromuscular junction thereby inhibiting striated muscle contractions. In the majority of pain syndromes where botulinum toxin type A is effective, inhibiting muscle spasms is an important component of its activity. Even so, the reduction of pain often occurs before the decrease in muscle contractions suggesting that botulinum toxin type A has a more complex mechanism of action than initially hypothesized. Current data points to an antinociceptive effect of botulinum toxin type A that is separate from its neuromuscular activity. The common biochemical mechanism, however, remains the same between botulinum toxin type A's effect on the motor nerve or the sensory nerve: enzymatic blockade of neurotransmitter release. The antinociceptive effect of the toxin was reported to block substance P release using in vitro culture systems. The current investigation evaluated the in vivo mechanism of action for the antinociceptive action of botulinum toxin type A. In these studies, botulinum toxin type A was found to block the release of glutamate. Furthermore, Fos, a product of the immediate early gene, c-fos, expressed with neuronal stimuli was prevented upon peripheral exposure to the toxin. These findings suggest that botulinum toxin type A blocks peripheral sensitization and, indirectly, reduces central sensitization. The recent hypothesis that migraine involves both peripheral and central sensitization may help explain how botulinum toxin type A inhibits migraine pain by acting on these two pathways. Further research is needed to determine whether the antinociceptive mechanism mediated by botulinum toxin type A affects the neuronal signaling pathways that are activated during migraine.

Botulinum toxin a improved burning pain and allodynia in two patients with spinal cord pathology

OBJECTIVE

To report the effect of botulinum toxin A in two patients with burning pain and allodynia of spinal cord origin.

DESIGN, SETTING, PATIENTS

Two patients with spinal cord lesions at the cervical level (tumor and stroke) experienced exquisite skin sensitivity and spontaneous burning pain in dermatomes corresponding to the cord lesions. Botulinum toxin A (Botox) was injected subcutaneously at multiple points (16 to 20 sites, 5 units/site) in the area of burning pain and allodynia.

RESULTS

Both patients reported significant improvement in spontaneous burning pain and allodynia in visual analogue scale and clinical measures. The analgesic effect of botulinum toxin A lasted at least 3 months and was sustained over follow-up periods of 2 and 3 years with repeated administration at 4-month intervals.

CONCLUSION

Subcutaneous application of botulinum toxin A relieved central burning pain and allodynia in two patients with spinal cord pathology.

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

Botulinum toxin A and the cutaneous nociception in humans: a prospective, double-blind, placebo-controlled, randomized study

Aside from temporary chemodenervation of skeletal muscle and potential anti-inflammatory effects, a genuine peripheral antinociceptive effect of Botulinum Neurotoxin Type A (BoNT/A) has been suspected. To evaluate the effect of BoNT/A on cutaneous nociception in humans, 50 healthy volunteers received subcutaneous injections of 100 mouse units (MU) BoNT/A (Dysport) and placebo. Both forearms of each subject were treated in a double-blind fashion, one with verum, one with placebo. Heat and cold pain thresholds within the treated skin areas were measured with quantitative sensory testing (QST) and pain thresholds were evaluated with local electrical stimulation (ES). The tests were done before treatment, and after 4 and 8 weeks. No major side effects were noted. All participants completed the study. Heat and cold pain thresholds increased from baseline to week 4 by 1.4 degrees C for verum and by 1.1 degrees C for placebo. From baseline to week 8, the thresholds increased by 2.7 degrees C for verum and by 1.2 degrees C for placebo. Electrically induced pain thresholds shifted from baseline to week 4 by -0.07 mA for verum and by 0.01 mA for placebo. From baseline to week 8, the thresholds increased by 0.10 mA for verum and by 0.11 mA for placebo. None of these differences was statistically significant. The study shows that there is no direct peripheral antinociceptive effect of BoNT/A in humans. The efficacy of BoNT/A in various pain syndromes must be explained by other pathways such as chemodenervation or anti-inflammatory effects.

Botulinum toxin for the treatment of musculoskeletal pain and spasm

The impressive pain relief experienced by sufferers of dystonia and spasticity from intramuscular injections of botulinum toxin suggested that patients with other chronic, musculoskeletal pain conditions also may benefit. However, there have been relatively few placebo-controlled studies of botulinum toxin in such non-neurologic conditions as myofascial pain syndrome, chronic neck and low back pain, and fibromyalgia; the results of these studies have not been impressive. One explanation for the lack of positive findings may be the lack of clinically evident muscle spasms (overactivity), despite the presence of muscle tenderness, tightness, or trigger points. Clinical observations of pain relief from injections of botulinum toxin for dystonia and spasticity and its apparent efficacy in treating migraine suggest an anti-nociceptive action independent of its neuromuscular junction-blocking action. Evidence from animal experiments supports this notion, and other data provide plausible physiologic mechanisms in the periphery and central nervous systems. These involve modulation of the activity of the neurotransmitters glutamate, substance P, calcitonin gene-related peptide, enkephalins, and others. However, even if botulinum toxin is firmly established as an analgesic, there is insufficient clinical evidence of its efficacy in treating non-neurologic, chronic, musculoskeletal pain conditions.

Botulinum toxin in pain management of soft tissue syndromes

Botulinum toxin is approved for the treatment of muscle overactivity associated with several disorders, such as dystonias. However, control of muscle spasm often results in pain relief as well. Effective relief of pain associated with myofascial pain syndrome provides a model for the use of botulinum toxin to relieve pain associated with other types of soft-tissue syndromes, such as fibromyalgia. Although the mechanisms that trigger the pain in these syndromes vary, recent data suggest that a central neuroplastic mechanism may contribute to many complex pain syndromes. Botulinum toxin therapy may be particularly useful in soft-tissue syndromes that are refractory to traditional treatment with physical therapy, electrical muscle stimulation, and other approaches. Although not used as first-line therapy for pain relief, botulinum toxin may decrease pain long enough for patients to resume more conservative therapy. A primary benefit of treatment with botulinum toxin is its long duration of action. Several studies have demonstrated the efficacy of botulinum toxin types A and B in treating several neuropathic pain disorders. Proper patient selection, injection technique, and dosing are critical to obtaining the best outcomes in managing pain with botulinum toxin. Additional study is needed to better characterize its use for the treatment of pain.

Possible mechanisms for the effects of botulinum toxin on pain

The therapeutic effects of botulinum toxin are principally, if not exclusively, derived from an alteration in the release of acetylcholine (ACh) at pre-synaptic neurons. The rationale for how these effects could be beneficial in conditions characterized by excessive muscle contraction is clear, but the hypotheses regarding botulinum toxin-induced effects on pain are highly speculative. We explore five possible mechanisms by which botulinum toxin could directly or indirectly alter pain, including: 1) changes in the sensitivity and response patterns of group III and IV muscle nociceptors, 2) diminished activity in the gamma-motor neurons and consequent changes in muscle spindle afferents, 3) alterations in cholinergic control of vascular and autonomic functions, including neurogenic inflammation, 4) induced neuroplastic changes in the processing of afferent somatosensory activity at multiple levels of the neuroaxis, and 5) direct non-cholinergic effects on pain afferents.

Botulinum toxin therapy for myofascial pain disorders

Myofascial pain disorder can originate from various muscles in the body. Numerous therapeutic approaches have been used to treat myofascial pain syndrome with varying success. Botulinum toxin neurolysis may become an important treatment regimen because it sustains relaxation of muscles. There is a growing body of clinical evidence for the efficacy of botulinum toxin in the treatment of painful myofascial conditions. The conditions that have been investigated include chronic low back pain, chronic cervical-associated headache, myofascial pain, myofascial pain syndrome and pain from chronic muscle spasm, and refractory myofascial pain. One of these studies was an open-label, exploratory pilot study into the cervicothoracic and lumbosacral regions using a novel injection technique.

Randomized controlled trial of botulinum toxin A for chronic myogenous orofacial pain

The purpose of this study was to determine whether botulinum toxin A (BTX-A) was efficacious for the treatment of chronic moderate to severe jaw muscle pain in females. This was a randomized double-blind, placebo-controlled crossover trial of BTX-A. Twenty five units injected into each temporalis muscle and 50 U injected into each masseter muscle using three sites per muscle with 0.2 cm(3) per site. Data were collected at baseline, 8, 16, 24 weeks, with crossover occurring at 16 weeks. Primary outcome variables were pain intensity and unpleasantness, measured by horizontal visual analog scale (VAS). Secondary outcome variables were maximum interincisal opening without and irrespective of pain, muscle palpation tenderness (12 points), and four general questions. Fifteen female patients were enrolled (18-45 years), but only ten completed the trial. Of those who finished, no statistically significant difference was found in pain intensity (P=0.10), unpleasantness (P=0.40), palpation muscle tenderness (P=0.91), or the three general questions (P=0.64, P=0.66, P=0.67). Statistical significance was achieved for maximum opening without pain (P=0.02) and irrespective of pain (P=0.005) with the BTX-A arm having a relative decreased opening. No statistically significant difference was observed in any outcome measures except maximum opening, which showed BTX-A patient opening less wide than placebo. The results do not support the use of BTX-A in the treatment of moderate to severe jaw muscle pain in this patient population.

Botulinum toxin type A injection in the treatment of lichen simplex: an open pilot study

Recalcitrant pruritus is a hallmark of lichen simplex, a localized variant of atopic dermatitis. Acetylcholine has been demonstrated to mediate pruritus in atopic dermatitis. This open pilot study was done to determine the therapeutic effect of blocking acetylcholine release with botulinum toxin A in highly pruritic lichen simplex. Botulinum toxin A (Dysport) was injected intradermally into 5 circumscribed lichenoid lesions in 3 patients suffering from recalcitrant pruritus. No corticosteroids or any other specific topical therapy was administered. Pruritus subsided within 3 to 7 days in all 3 patients. Within 2 to 4 weeks all lesions cleared completely. No recurrences were noted over a 4-month follow-up. In one patient lichen simplex developed on the contralateral shin, which responded equally to a subsequent injection. We concluded that lichen simplex-associated pruritus can be overcome by intradermal botulinum toxin A injection. Acetylcholine appears to be a dominant pruritic mediator in this condition.

Adjuvant botulinum toxin A in dyshidrotic hand eczema: a controlled prospective pilot study with left-right comparison

OBJECTIVE

Dyshidrotic hand eczema is a therapeutic challenge. A prospective pilot study was performed with left-right comparison in order to investigate whether chemical de-innervation of sudoriferic nerves would be superior to standard therapy with topical corticosteroids.

BACKGROUND

Botulinum toxin A (BTXA) is a potent inhibitor of acetylcholine release, that induces eccrine sweat production and release. Inhibition of sweating by other measures such as tap water iontophoresis has been shown to be beneficial in dyshidrotic hand eczema.

METHODS

Eight adult patients suffering from dyshidrotic hand eczema (atopic type) were included in a prospective, side-by-side controlled clinical pilot study using topical corticosteroids on both hands in combination with intracutaneous injections of 100 units of BTXA (Botox) on the more severely affected hand on day 1. The dyshidrotic hand eczema was classified using the DASI (Dyshidrotic Eczema Area and Severity Index) before treatment (0), after 1 week, 4 weeks and 8 weeks.

RESULTS

Six patients completed the study, two dropped out because of social and personal reasons. The mean DASI score changed from 28 to17 with topical therapy alone and from 36 to 3 with adjuvant BTXA (P < 0.01). Itching and vesiculation were inhibited earlier when using the combination of corticosteroids and BTXA. There was one relapse in the corticosteroid group. Relapses have not been seen in the BTXA group.

CONCLUSIONS

Interruption of sweating by BTXA improves the outcome and reduces relapses in patients with dyshidrotic hand eczema. BTXA is antipruritic as well suggesting that it does not only interact with acetylcholine release but substance P.

Botulinum toxin type A and other botulinum toxin serotypes: a comparative review of biochemical and pharmacological actions

Botulinum toxin type A is an important therapeutic agent for the treatment of movement and other disorders. As the clinical uses of botulinum toxin type A expand, it is increasingly important to understand the biochemical and pharmacological actions of this toxin, as well as those of other botulinum toxin serotypes (B-G). Botulinum neurotoxin serotypes exhibit differences in neurotoxin complex protein size, percentage of neurotoxin in the activated or nicked form, intracellular protein target, and potency. These properties differ even between preparations that contain the same botulinum toxin serotype due to variations in product formulations. As demonstrated in preclinical and clinical studies, these differences result in a unique combination of efficacy, duration of action, safety, and antigenic potential for each botulinum neurotoxin preparation.

Differential inhibition by botulinum neurotoxin A of cotransmitters released from autonomic vasodilator neurons

The role of the soluble NSF attachment protein receptor (SNARE) protein complex in release of multiple cotransmitters from autonomic vasodilator neurons was examined in isolated segments of guinea pig uterine arteries treated with botulinum neurotoxin A (BoNTA; 50 nM). Western blotting of protein extracts from uterine arteries demonstrated partial cleavage of synaptosomal-associated protein of 25 kDa (SNAP-25) to a NH2-terminal fragment of approximately 24 kDa by BoNTA. BoNTA reduced the amplitude (by 70-80%) of isometric contractions of arteries in response to repeated electrical stimulation of sympathetic axons at 1 or 10 Hz. The amplitude of neurogenic relaxations mediated by neuronal nitric oxide (NO) was not affected by BoNTA, whereas the duration of peptide-mediated neurogenic relaxations to stimulation at 10 Hz was reduced (67% reduction in integrated responses). In contrast, presynaptic cholinergic inhibition of neurogenic relaxations was abolished by BoNTA. These results demonstrate that the SNARE complex has differential involvement in release of cotransmitters from the same autonomic neurons: NO release is not dependent on synaptic vesicle exocytosis, acetylcholine release from small vesicles is highly dependent on the SNARE complex, and neuropeptide release from large vesicles involves SNARE proteins that may interact differently with regulatory factors such as calcium.

The antimicrobial properties of melanocytes, melanosomes and melanin and the evolution of black skin

A biological issue that has not been satisfactorily resolved is the role of melanin in skin and other animal tissues. A hypothesis is outlined here to account for the evolution of black skin and the ubiquity of melanin in vertebrate tissues. Evidence is presented that melanization of skin and other tissues forms an important component of the innate immune defense system. A major function of melanocytes, melanosomes and melanin in skin is to inhibit the proliferation of bacterial, fungal and other parasitic infections of the dermis and epidermis. This function can potentially explain (a) the latitudinal gradient in melanization of human skin; (b) the fact that melanocyte and melanization patterns among different parts of the vertebrate body do not reflect exposure to radiation; (c) provide a theoretical framework for recent empirical findings concerning the antimicrobial activity of melanocytes and melanosomes and their regulation by known mediators of inflammatory responses.