Baclofen is used in MS to reduce muscle stiffness and spasms. It works by reducing signals to and from specific nerve receptors in the brain and spinal cord, dampening down the effects of spasticity. It's usually taken as a tablet. However, some people find that tablets don't help enough, or that the side effects are unbearable.
This is because it's difficult for oral baclofen to pass through the blood-brain barrier, the brain's protective mechanism which stops unwanted substances - and some drugs - entering the central nervous system. This can lead to too much baclofen in the bloodstream and results in unwanted side effects such as weakness, dizziness and fatigue. If this is the case, the use of intrathecal baclofen (ITB) may be considered.
The intrathecal space is the fluid filled cavity that surrounds your spinal cord within the spine. Drugs delivered intrathecally are passed directly into this cavity and so are supplied straight to the appropriate nerve receptors. This is a much more efficient delivery method which bypasses some of the side-effects of oral tablets, provides a more consistent effect and allows a much lower dose (approximately 100 times less than the oral dose) of baclofen to be used.
Not everyone responds to, or is appropriate for intrathecal baclofen, so initially you would have a trial. This is carried out in hospital and involves a relatively large amount of baclofen being injected directly into your cerebrospinal fluid (CSF) via a lumbar puncture or a temporary intrathecal catheter. The baclofen reaches its maximum effect around four to six hours after injection and then starts to wear off. The effects are monitored to see if you respond or not, and then a decision will be made between you and the team as to whether to proceed with having a pump implanted to provide you with long-term treatment.
Treatment with intrathecal baclofen involves surgically implanting a pump under the skin in your abdomen near the waistline. This is carried out under a general anaesthetic. The pump is about two and a half centimetres thick and about seven and a half centimetres wide. It consists of a reservoir, which stores the intrathecal baclofen, and a catheter which connects the reservoir to the cerebrospinal fluid in the intrathecal space.
The complete system remains hidden under the skin. You usually can't see the pump through clothes, but if you are very slim and wear tight clothing, you may be able to see the outline of the pump. It is fine to wash and shower when the pump is in place, but initially following surgery you will need to keep the wound where the pump has been implanted dry, usually for around seven to 10 days, whilst it heals.
The pump will be filled with baclofen in theatre and is programmed to release prescribed doses of baclofen, the actual infusion rate and dosage will be tailored to your needs. The pump has a microchip inside it, which allows it to be programmed by an external device which is placed lightly on the skin over the pump. This can be used to adjust the dose, rate and timing of the baclofen.
The pump will require regular refills, the time between refills can vary, but is usually every four to six months. The reservoir is refilled by placing a needle through the skin and into the refill port. This can be a bit uncomfortable but doesn't require surgery.
Pumps are powered by a battery which lasts for around five to seven years, at which time your pump will need to be replaced. This involves removing your pump from the abdomen and attaching a new pump to the existing catheter, again this is usually carried out under a general anaesthetic.
Once an intrathecal baclofen pump is in place and your dose is stabilised, the aim is to reduce and possibly stop any other anti-spasticity medication you are taking. As with all medications there are possible side effects of intrathecal baclofen, these include possible changes to the bladder (positive or negative), bowel or sexual function.
One of the more recent goals of using intrathecal baclofen is to improve cognitive function, which can be affected by the oral treatments, and improve walking ability. Traditionally intrathecal baclofen was reserved for wheelchair users. However, recent studies have shown that, in carefully selected patients who are still walking, walking ability can be preserved for several years whilst treating spasticity with intrathecal baclofen. So it should no longer be thought of as a last resort, and is being used more frequently in people who are still walking, and therefore more likely to be in work, and keen to avoid medications that impact on their cognition.
Because of the surgical procedure, the need to refill and potentially replace pumps, together with the obvious risk of infection, intrathecal baclofen is only available in the UK in a few specialist centres.