Spasticity and Botulinum Toxin After Stroke: What It Does and Does Not Do

Botulinum toxin reliably reduces the muscle tone of spasticity after a stroke, but it does not reliably restore voluntary movement: it eases care, pain and positioning rather than giving the limb back. Spasticity is a velocity-dependent increase in tone that affects around 25% of stroke survivors, and the honest thing to say about the injection is that reducing tightness and regaining control are two different problems¹².

I came to this one with the wrong expectations, and I would rather you did not. My left hand had curled into a tight fist in the months after my stroke, and when the injections were first mentioned I heard “the treatment that fixes the hand”. It is not that. Understanding what it actually does saved me a lot of disappointment, and it is part of the wider picture of what neuro-rehabilitation can and cannot do. If you want the movement side of the story, that lives in arm and hand recovery after stroke.

What is spasticity?

Spasticity is a velocity-dependent increase in muscle tone: the faster you try to move the limb, the harder it resists, because the stroke has disrupted the signals that normally keep tone in check. It affects around 25% of stroke survivors overall, and it is more common in people with a weak or paralysed limb³.

In practice it shows up as tightness that pulls a joint into a fixed pattern: a hand clenched into a fist, an elbow bent up towards the chest, a foot pointing down and turning in. Left alone it can ache, make the skin in a clenched palm hard to keep clean, and eventually stiffen the joint permanently. Mine was worst in the hand and the elbow, and it was worse when I was tired or trying too hard. Spasticity is one of several complications a rehabilitation team watches for, alongside things like shoulder pain after stroke.

How is spasticity measured?

Clinicians grade spasticity with a simple bedside tool, most often the Modified Ashworth Scale, which rates the resistance felt when a limb is moved through its range from 0 (no increase in tone) up to 4 (rigid). It is quick and subjective, but it gives the team a shared number to track before and after treatment⁴.

The point of measuring is to separate the two things that often get blurred: how tight a muscle is, and how much you can move it yourself. You can have severe tightness and near-zero voluntary control, or mild tightness with useful movement, and the plan is completely different for each. Tracking it over time is part of the broader business of measuring progress in rehabilitation.

What does botulinum toxin actually do?

Botulinum toxin reduces muscle tone by blocking the chemical signal at the junction between nerve and muscle, so an overactive muscle relaxes; the evidence that it reduces tone is strong and consistent. It is injected in carefully calculated doses into the specific muscles that are pulling a joint out of position, sometimes guided by ultrasound or electrical stimulation to place it accurately¹.

What it does not do is give you control back. In the BoTULS trial, botulinum toxin improved muscle tone and helped with some specific arm tasks, but it did not improve overall arm function or the ability to use the arm in everyday life². That is the sentence I wish someone had said to me plainly: it quietens the muscle that is fighting you, but a quiet muscle is not the same as a muscle you can move. The signal that tells the hand to open has to be rebuilt through practice, which is the work of neuroplasticity and task-specific training, not the needle.

So why have it at all?

The real value of botulinum toxin is easing care, comfort and positioning: relaxing a clenched hand or a stiff arm so that washing, dressing, splinting and positioning become possible, and the ache of a permanently tight muscle eases. NICE frames it as a treatment for focal spasticity that is interfering with function, care or comfort, not as a way to restore movement⁵.

This is where it earned its place for me. Once the fist relaxed a little, my occupational therapist could actually get the hand flat to clean it, the palm stopped breaking down, and a resting splint that had been impossible to fit finally went on at night. None of that is dramatic, and none of it is “using the hand again”, but living with a hand that can be opened, cleaned and rested is genuinely better than living with one that cannot. Making daily care easier and less painful is a worthwhile goal in its own right, and it sits inside the wider work of the occupational therapy team and the rehabilitation team as a whole.

How the treatment works in practice

Botulinum toxin takes a few days to start working, reaches full effect at around 2 to 4 weeks, and wears off over about 3 to 4 months, so it is repeated and always paired with therapy rather than used alone. The reduced-tone window is meant to be used: for stretching, splinting, positioning and practice while the muscle is quieter¹.

That pairing matters. On its own the injection just buys a few months of looser tone; combined with hands-on therapy in that window it can help maintain range, prevent a joint stiffening for good, and make other rehabilitation possible. It is one tool used inside a plan, and how often and how much therapy sits alongside it is the subject of how much therapy do you need. It is generally well tolerated, with the main issues being temporary local weakness, bruising, or occasional spread to nearby muscles.

Setting honest expectations

The honest summary is that tone is not function: botulinum toxin reliably makes a spastic muscle less tight, but it does not reliably make the limb work, and going in expecting the second leads to disappointment. Guideline bodies are careful to frame it as easing care, pain and positioning, not as a movement restorer¹⁵.

It also is not for everyone. Spasticity affects only around 25% of stroke survivors, and much of it is mild and managed with stretching, positioning and splinting rather than injections³. Whether it is right for you depends on which muscles are overactive, what problem they are causing, and what you and your team are trying to achieve, which is exactly the kind of decision goal-setting in rehabilitation is built around. A rehabilitation team who can assess the limb decides that, not a website, and not a hope pinned on the wrong treatment.