Botulinum Toxin Injections for Neurological Disorders

Introduction to botulinum toxin
How does botulinum toxin work?
What is botulinum toxin used for?
What is involved in having a botulinum toxin injection?
What are the possible side effects of a botulinum toxin injection?
How much does botulinum toxin therapy cost?

Introduction to botulinum toxin

Botulinum toxin injections for neurological disorders Botulinum toxin is actually a neurotoxin that is produced by the bacterium responsible for botulism, Clostridium botulinum. The name comes from the latin word for sausage ('botulus') and comes from a German physician who described the poisoning after the ingestion of sausage. The neurotoxin works by weakening the muscles and stopping them from contracting very well, which can lead to paralysis.

The commercial medical drug is a highly purified form of this toxin that can actually be very useful for lots of different medical conditions, not just the cosmetic ones for which it is better known. Some of these are neurological conditions due to muscles being too tight, while it can also be helpful in some other medical indications such as excessive sweating and drooling.

How does botulinum toxin work?

The therapeutic effects of the neurotoxin have been known for some time now with the first clinical use of the preparation in strabismus, or squint, in the 1970's. There are two commercially available forms of the most common preparation, botulinum toxin type A, in Australia. They are Botox^TM (Allergan pharmaceuticals) and Dysport^TM (Ipsen pharmaceuticals). The term 'botox' is often used interchangeably with botulinum toxin, but this can be problematic given the very different dose available of these two common preparations.

The preparations are purified forms of the toxin, and contain rather minute quantities of the toxin produced by the bacterium. Usually, the infection that produces this toxin, botulism, is quite serious and can cause weakness and even paralysis. The toxin does this by stopping the nerve fibres that control muscles from working the way they normally do. Usually, nerves release a chemical called acetylcholine from its ending which signals for muscle to contract. Botulinum toxin stops this substance from being released, and so the muscle does not contract. While this action is dangerous if released by the infection, when purified and injected, it can be incredibly useful in diseases where the muscles are too tight, or where doctors want to stop the release of acetylcholine.

By making sure the injections are in just the right spot, botulinum toxin can provide very effective treatment for lots of conditions with very few side effects. Although the weakening of the muscle is felt to be important, some recent research suggests that some conditions like dystonia, which is an involuntary tightening of muscle, may be the result of abnormal incoming signals from nerves and muscle. This has led to recent thinking that the toxin may exert its beneficial effect by interrupting these incoming signals to the brain as well.

What is botulinum toxin used for?

Botulinum toxin injections for neurological disorders While Botox may be better known as a tool for cosmetic surgeons, below are some of the conditions that are treated very effectively by botulinum toxin.

Blepharospasm

Blepharospasm refers to a spasming eyelid ('blephara' being the eyelid and spasm meaning rapid movement). This can be a very unpleasant condition for a sufferer. Patients complain of repetitive blinking and sometimes, an inability to keep the eyes open.

To treat this, very small amounts of botulinum toxin can be injected through a very fine needle into the eyelids. This partially paralyses the muscle and provides great relief.

Hemifacial spasm

Hemifacial spasm is similar to blepharospasm, with an involuntary contraction of the muscles of the face on one side. The most frequently identified cause is a small loop of an arterial vessel just inside the base of the skull, which is pressing on the facial nerve which controls those facial muscles. Once again, injections around the eye and sometimes also the lower face can help.

Cervical dystonia

Cervical dystonia means abnormally high muscle tone (dystonia) in the neck (cervical) and can result in various positions of the head. Some of these may involve the neck being rotated and pulled in a certain direction or down towards the chest. This condition is also sometimes called torticollis or 'wry neck'.

The injection partially paralyses the muscle and frees up movement of both the neck and also the shoulders. In this case, the toxin is usually injected with the help of an electromyography (EMG) machine that can sense the electrical currents of muscles to make sure that it is being injected in exactly the right spot.

Other dystonias

Like with cervical dystonia, other muscles can also have 'abnormal tone' and be too tight. This can limit the amount of movement that is possible. By injecting these muscles with botulinum toxin, they can be freed up and allowed to move more, providing effective treatment for dystonias.

Spasticity

Botulinum toxin injections for neurological disorders Spasticity is a condition where there is excessive muscle tone, like dystonia, but follows injury to the brain or spinal cord. Often, very large doses of the injection are given into the 'spastic' muscles with a specific aim in mind e.g. comfort, mobility or hygiene. Other treatments such as physiotherapy and the use of plaster casts may be important.

Drooling in cerebral palsy and Parkinson's disease

In children with cerebral palsy and in adults with Parkinson's disease, there is often excessive drooling, and this can be helped by injecting botulinum toxin into the salivary glands beneath the jaw and on the side of the face that produce the saliva. Often, there is not actually an excess of saliva produced, but a lack of swallowing which normally clears saliva. Acetylcholine (the substance that botulinum toxin blocks) not only controls muscles but also controls the salivary glands and tells them to produce saliva. The toxin basically lowers the drive to create saliva and so can prevent drooling with few side effects.

Hyperhidrosis

Hyperhidrosis means there is an excessive production of sweat from the glands in the skin, which can be very troublesome for some. Acetylcholine is also produced by nerves and stimulates sweat production in the skin; therefore it can be blocked with toxin.

Other

Other conditions that can be treated with botulinum toxin include 'spasmodic dysphonia' (where the muscles that control speech in the voice box become too tight), tremor, some hyperactive bladder disorders, and occasionally even headache.

What is involved in having a botulinum toxin injection?

A botulinum toxin injection is usually a quick and relatively simple procedure that can be done in a doctor's office. Firstly, the area for injection will be cleaned. There may be a little pain or pressure associated with the injection related to the needle and fluid itself, but a local anaesthetic agent is usually not required. The actual injection is just like having a vaccination shot, with a smaller amount of liquid being injected into the desired area.

The effects (both the good and bad if present) can be variable but wear off in time (usually within 3-4 months) and so the injection will probably have to be repeated then.

No preparation is needed before you go to have an injection. If you are using a drug that thins the blood aside from aspirin, the clinician may wish to know.

What are the possible side effects of a botulinum toxin injection?

Botulinum toxin injections for neurological disorders Botulinum toxin in the right hands in the commonly used doses is a relatively safe procedure and there are actually very few serious side-effects. The local side-effects of injection will be different depending on the area into which it is being injected. If injected to treat a spasming eyelid for example, some possible side-effects include drooping of the eyelid, blurred vision, and over production of tears and even some local bruising.

Often after injection, there can be a little bit of excessive weakness in the muscles and if injected into an area like the neck can result in difficulties in swallowing, speaking and even cause noisy breathing. This is because the injection has found its way into some other areas which is sometimes difficult to avoid because of the anatomy.

More general side-effects can include some pain around the site of injection, a rash, some itchiness, headache and tiredness. There may also occasionally may be flu-like symptoms which are usually shortlived.

Aside from the above, there are some serious side effects of botulinum toxin injections but they are exceedingly rare.

Botulinum toxin is generally avoided during pregnancy, as is breastfeeding in the days following an injection.

How much does botulinum toxin therapy cost?

In Australia, the Phamaceutical Benefits Scheme (PBS) fully subsidises the cost of the toxin preparation for only the conditions blepharospasm, hemifacial spasm and torticollis. In addition, the doctor may levy a charge for the injection procedure itself, which may or may not be part or fully recompensable under Medicare depending on the procedure.

Article kindly reviewed and written by:

Dr Karl Ng MB BS (Hons 1) MRCP FRACP CCT Clinical Neurophysiology (UK)
Consultant Neurologist, Royal North Shore Hospital
Sydney North Neurology & Neurophysiology (download referral form and map)
Conjoint Senior Lecturer, University of Sydney and Editorial Advisory Board Member of the Virtual Neuro Centre

More information

For more information on neurological disorders that affect movement, and their treatments, see Neurological Rehabilitation and Movement Disorders.

Reference

General references

Handbook of Botulinum Toxin Treatment. 2nd ed. Eds. Moore P, Naumann M. 2003, Blackwell Science Ltd.
Spasticity: Etiology, Evaluation, Management and the Role of Botulinum Toxin Type A. Muscle and Nerve 1997, Suppl 6.

Specific references

Allergan Australia. Botulinum toxin type A [online]. MIMS Online [cited 6 January 2008]. Available from URL: http://www.mims.com.au
Ng K, Jones SJ. The "enhanced N35" somatosensory evoked potential: its associations and potential utility in the clinical evaluation of dystonia and myoclonus. Journal of Neurology 2007; 254: 46-52.
Ramachandran T. Botulinum toxin: Dystonia treatment [online]. WebMD [cited 6 January 2008]. Available from URL: http://www.emedicine.com
Vaile L, Finlay F. Is injection of botulinum toxin type A effective in the treatment of drooling in children with cerebral palsy? Archives of Disease in Childhood. 91(10): 862-3, 2006.
Medicare Benefits Schedule, Dept of Health and Ageing, Australian Government, 1 Nov 2007.