Spasticity is a feeling of muscle stiffness, tightness, or involuntary spasms caused by nerve damage from multiple sclerosis. It affects more than 80% of people with MS at some point during the disease and ranges from a mild sensation of tightness to severe, painful contractions that make movement difficult. The legs are most commonly affected, though spasticity can occur in any muscle group.
What Spasticity Feels Like
At its mildest, spasticity feels like muscles that are constantly a little tight or resistant when you try to move. You might notice stiffness in your legs first thing in the morning or after sitting for a long time. At the other end of the spectrum, spasticity can cause sudden, uncontrollable jerking movements or sustained contractions that lock a limb in one position. These spasms can wake you up at night and make it hard to walk, get dressed, or sit comfortably.
Spasticity also commonly causes pain in and around joints, particularly low back pain. The stiffness isn’t just uncomfortable. It pulls on joints and changes how you hold your body, which creates secondary pain that can be just as disruptive as the spasms themselves.
Why MS Causes Spasticity
Your brain normally sends two types of signals down the spinal cord to control muscle movement: signals that activate muscles and signals that keep them relaxed. These work in balance so your muscles contract when you want them to and stay loose when you don’t. In MS, the immune system damages the protective coating around nerve fibers, which disrupts this balance.
Specifically, the pathways responsible for keeping muscles relaxed get damaged more than the pathways that activate them. The result is that your stretch reflex, the automatic tightening response muscles have when they’re pulled, becomes overactive. Normally, inhibitory circuits in your spinal cord dampen this reflex so your muscles don’t tighten up every time you move. When MS lesions interrupt the signals feeding those circuits, the reflex fires too easily and too strongly. Your muscles tighten when they shouldn’t, resist being stretched, and sometimes contract on their own.
Common Triggers That Make It Worse
Spasticity in MS isn’t constant at the same level. Certain factors can temporarily ramp it up, and recognizing them gives you some ability to manage flare-ups. In one study of MS patients, 90% identified stress and anxiety as making their spasticity worse, and 80% reported muscle fatigue as a trigger.
Temperature is another major factor. Both outside cold (reported by 60% of patients) and outside heat (also 60%) worsened spasticity, with indoor cold environments being even more problematic at 70%. Other triggers include:
- Urinary tract infections and bladder or bowel issues like constipation
- Lying on your back, which 50% of MS patients in the study linked to worse spasticity
- Skin irritation such as pressure sores or ingrown nails
- Humidity and atmospheric pressure changes
- Physical jolts like driving over bumps in the road
Some of these, like infections and constipation, are treatable problems on their own. Addressing them often brings spasticity back down without any change in spasticity-specific treatment.
How Severity Is Measured
Clinicians typically assess spasticity using a standardized scale called the Modified Ashworth Scale. During an exam, a clinician moves your limb through its range of motion and rates how much resistance your muscles put up. The scale runs from 0 (no increase in muscle tone) through intermediate grades where there’s a “catch” or resistance during movement, up to 4, where the affected limb is completely rigid and can’t be moved. This gives your care team a baseline to track whether your spasticity is getting better or worse over time and whether treatments are working.
Treatment Options
Oral Medications
The first-line medication for MS spasticity is baclofen, which works by mimicking a chemical messenger in your spinal cord that calms overactive nerve signals. It’s typically started at a low dose and gradually increased. Tizanidine is another common option that reduces spasticity through a different mechanism. It can be used on its own or combined with baclofen when one medication alone isn’t enough. Both medications can cause drowsiness, so finding the right dose is a balancing act between reducing stiffness and staying alert enough for daily life.
Physical Therapy and Stretching
Stretching has long been a core part of managing spasticity, though its effectiveness depends on the approach. Static stretching of tight muscles over several weeks can change how much resistance those muscles produce. Some evidence suggests that techniques using casts or braces to hold a muscle in a stretched position for extended periods are more effective than manual stretching alone. Physical therapy for spasticity works best when combined with other treatments rather than used as a standalone approach.
Targeted Injections
When spasticity is concentrated in specific muscle groups, botulinum toxin injections can temporarily weaken those muscles and reduce tightness. This is particularly useful when a few muscles are causing most of the problems, like calf muscles that make walking difficult.
Implanted Pumps for Severe Cases
For people whose spasticity doesn’t respond to oral medications, or who can’t tolerate the side effects at the doses they need, a small pump can be surgically implanted under the skin to deliver medication directly into the fluid surrounding the spinal cord. This approach requires much smaller doses than oral medication and typically produces fewer side effects like drowsiness. Candidates generally need to have tried at least six weeks of oral treatment first, and they undergo a test dose to confirm that the direct delivery actually helps before the pump is placed.
What Happens Without Treatment
Spasticity that goes unmanaged tends to get worse over time and can cause permanent changes. Muscles that stay tight for months or years can shorten permanently, creating contractures where a joint becomes fixed in one position and can no longer straighten or bend fully. Once a contracture forms, it’s very difficult to reverse.
Beyond contractures, chronic untreated spasticity leads to a cascade of problems. Pain from tight muscles disrupts sleep. Reduced mobility increases the risk of falls. Rigid limbs pressing against bony areas of the body create pressure ulcers. Daily activities like bathing, dressing, and transferring from a wheelchair become harder, increasing dependence on caregivers. Managing spasticity early, even when it seems mild, helps prevent these complications from developing.