These neurological conditions affect muscle movement in separate ways

Spasticity is a neurological condition that disrupts muscle movement. Dystonia shares the same resume. In many ways, the two conditions resemble each other ― so much so that they can be difficult to tell apart.

But while spasticity and dystonia may be similar, they’re distinctly different on multiple levels. How so? Let’s find out from neurologist Junaid Siddiqui, MD.

Spasticity vs. dystonia

In a basic explanation, spasticity and dystonia sound pretty much the same. Both trace their cause to a brain condition or brain damage that scrambles instructions sent to certain muscles within the body.

This faulty messaging results in muscles not behaving as they should. Symptoms from both conditions can appear in your arms, hands or legs, limiting your ability to move or do everyday tasks.

“Both dystonia and spasticity are physical manifestations of neurological dysfunction,” says Dr. Siddiqui.

It can be difficult for someone experiencing these symptoms to differentiate between spasticity and dystonia, notes Dr. Siddiqui. “It’s even possible to have dystonia, as well as spasticity from the same condition.”

But there are key differences that set spasticity and dystonia apart. Let’s break them down.

Effect on muscles

Spasticity brings a continuous muscle contraction that seems to lock a muscle into place, reports Dr. Siddiqui. These spasms apply constant tension that makes the muscle stiff and unable to move.

If spasticity affects your arm, for instance, you might have a bend at your elbow that you can’t straighten without applying force to move it. This results from overactivity of one set of muscles while the opposing muscles may be weak.

“You can feel increased tone from spasticity in the muscle, especially with passive movement,” adds Dr. Siddiqui.

But dystonia brings spasms to opposing muscles ― the agonist (which contracts to bring movement) and the antagonist (which relaxes to allow or control the movement at the same time).

“This co-contraction means both muscles are firing at once, meaning they don’t cooperate with each other,” explains Dr. Siddiqui.

This tug of war between opposing muscles can cause a shaky back-and-forth movement similar to a tremor. The competing muscles may also cause contortions by forcing limbs to twist and turn, leading to what looks like unusual poses.

When it happens

Spasticity is a static (or continuous) condition. The pose or positioning created by the continuous muscle contraction doesn’t change on its own. “It results in a posture that is there regardless of what the person is doing,” clarifies Dr. Siddiqui.

But dystonia is a dynamic (or fluctuating) situation that can come and go. It’s usually triggered by a motion that uses the affected muscles. “It comes out with activation,” he says. “It’s not present at rest.”

Starting point in the brain

While both spasticity and dystonia are neurological disorders rooted in your brain, they typically originate in different parts of it, says Dr. Siddiqui. Specifically:

  • Spasticity often involves an issue within your cerebral cortex, the “gray matter” that initiates muscle movement by sending signals through nerve pathways within your central nervous system. A problem with any of the “wires” along the tract within your brain or the spinal cord may result in spasticity.
  • Dystonia usually involves damage to your basal ganglia, a group of structures near the center of your brain that manage signals to your muscles. It can sometimes be seen with problems in other areas of your brain or nervous system.

Causes

Stroke or a severe head injury can cause the sort of internal brain damage that leads to either spasticity or dystonia. (As noted, the resulting condition often depends on where the damage takes place.)

But a host of other issues may also trigger either condition.

Spasticity could be caused by:

Dystonia could be linked to:

A medical history can help determine whether someone is dealing with spasticity or dystonia.

Treatments

Spasticity and dystonia are both lifelong conditions that can vary in severity, but they can be managed, states Dr. Siddiqui. Common nonsurgical approaches to reduce symptoms may include:

Each condition also has surgical options. Deep brain stimulation from implanted electrodes can sometimes tame dystonia, while intrathecal baclofen (ITB) therapy from a surgically implanted pump can be used for spasticity.

“For both conditions, there are a lot of ways we can help,” reassures Dr. Siddiqui.