Multiple sclerosis (MS) and stiff-person syndrome (SPS) are both autoimmune diseases that affect the nervous system. These conditions share several symptoms, like muscle stiffness, muscle spasms (cramps or twitches), trouble walking, and muscle pain. Because of this overlap, some people may face delays in getting the right diagnosis.

Is Stiff-Person Syndrome the Same as Multiple Sclerosis?

Stiff-person syndrome, formerly called stiff-man syndrome, is not the same as multiple sclerosis. SPS is a rare disease caused by an abnormal immune response. This neurological disorder affects only 1 to 2 people per million. Doctors sometimes mistake it for other autoimmune disorders, such as Parkinson’s disease or fibromyalgia.

In rare cases, someone might have MS and SPS at the same time. However, this is extremely uncommon.

While MS and SPS have similarities, they also have important differences. Below, we’ll explain how to tell MS and SPS apart and share more about stiff person syndrome.

1. SPS Doesn’t Cause Nerve Damage

MS and SPS have different causes, so their symptoms look and feel distinct.

In MS, the immune system attacks the central nervous system, causing physical damage. This damage, called lesions, forms in the brain and spinal cord. The symptoms depend on where the lesions are located. For example, some people may feel numbness, tingling, vision changes, or trouble moving. These symptoms are rare in SPS, though they can occur in some cases.

Scientists aren’t entirely sure how exactly SPS develops. However, it seems to be linked to immune system proteins called anti-GAD65 antibodies. In SPS, the body produces too many of these antibodies. The antibodies block certain enzymes, which lowers levels of a brain chemical called gamma-aminobutyric acid (GABA).

GABA helps control signals within the nervous system. When GABA levels drop too low, nerves can display too much electrical activity and send too many signals to the muscles. This causes the muscle spasms and stiffness seen in SPS. However, this process doesn’t usually cause nerve damage. Because of this, people with SPS typically don’t experience numbness or pins-and-needles sensations.

2. SPS Doesn’t Directly Cause Muscle Weakness

In MS, nerve damage in the brain and spinal cord can lead to muscle weakness. This happens because the damage in the brain and spine prevents nerves from communicating properly with muscles. This can limit strength and make movement harder.

In SPS, the nerve signals between the brain, spinal cord, and muscles aren’t blocked like they are in MS. So, SPS doesn’t directly cause muscle weakness. However, chronic muscle stiffness and spasms can make movement difficult in people with SPS. Over time, this can lead to muscle fatigue and secondary weakness.

3. SPS Usually Doesn’t Affect Coordination

Most people with MS develop ataxia (loss of muscle coordination), due to nerve damage. This can cause clumsiness, trouble walking or speaking, or tremors.

People with SPS may also have trouble walking or experience frequent falls. But this is usually due to muscle spasms, not a loss of coordination. Muscle stiffness can also reduce mobility and make movement uncomfortable or difficult for people with SPS.

4. SPS Doesn’t Lead to Dizziness

In MS, dizziness, vertigo, and balance problems are often among the earliest symptoms. These occur because brain lesions affect your sense of balance. People with MS may fall often or struggle to walk steadily.

People with SPS can also have balance issues and a higher risk of falling. However, this is usually due to muscle stiffness and painful muscle spasms, not neurological damage. Dizziness and vertigo aren’t symptoms of SPS.

5. MS and SPS Lead to Different Types of Breathing Problems

In rare cases, people with SPS may have trouble breathing if muscle spasms affect the chest or diaphragm muscles. These spasms can make the muscles rigid, sometimes causing a person to stop breathing suddenly. This can be life-threatening, but breathing symptoms in SPS usually happen only when the condition is severe.

In MS, breathing difficulties are caused by weakened breathing muscles. This weakness may start off mild but can worsen over time. Breathing symptoms in MS are usually different from those in SPS. People with MS may also experience chest tightness that makes breathing difficult, known as the MS hug.

6. SPS Can Cause Curvature of the Spine

Many people with SPS develop changes in the lower spine. This is known as hyperlordosis, or swayback. This happens when tightened muscles in the back and abdomen pull on the spine. Other people with SPS develop kyphosis, a forward rounding or hunching of the upper back.

Over time, these changes in the spine can lead to spinal cord compression — a type of spinal cord injury that can cause pain, weakness, or numbness. These nerve symptoms aren’t directly caused by SPS but can result from spine changes that sometimes result from SPS.

In MS, muscle weakness can make it hard to maintain good posture. This is typically an early symptom of the condition. Poor posture can lead to balance problems, back pain, and falls. However, MS doesn’t directly change the spine’s structure. That said, MS does increase the risk of scoliosis, a sideways curve of the spine.

7. MS and SPS Have Different Symptom Triggers

In MS, symptoms can worsen during periods called exacerbations, also known as flares or relapses. They can be triggered by being exposed to heat, smoking, giving birth, or developing an infection. Stress may also impact MS exacerbations for some people, although research on this is still unclear.

In SPS, symptoms are often triggered by cold temperatures, loud noises, physical touch, emotional stress, or sudden movements. These triggers can cause muscle spasms or stiffness to flare up with this rare disorder.

8. MS and SPS Can Occur With Different Disorders

Up to 80 percent of people with SPS have at least one other condition, called comorbidity. The most common comorbidities in SPS are diabetes, pernicious anemia, vitiligo, and autoimmune thyroid disease. In one study, people with SPS were six to 11 times more likely to have a psychological condition, such as anxiety or depression, compared to people without SPS.

People with MS often have other health conditions, too, but it’s hard to say exactly how common they are. Studies show a wide range of comorbidities in MS. The most common co-occurring conditions include depression, anxiety, high blood pressure, high cholesterol, and lung disease.

9. SPS Can Cause Anxiety Earlier On

Low levels of GABA in the brain are linked to anxiety and depression. Since people with SPS have lower GABA levels, they often experience increased anxiety. Anxiety can be one of the early signs of stiff-person syndrome, which is why SPS is sometimes misdiagnosed as a panic or anxiety disorder.

People with MS may also develop anxiety, but this usually happens after their diagnosis. According to the Multiple Sclerosis Association of America, about 43 percent of people with MS have an anxiety disorder. According to research in Multiple Sclerosis and Related Disorders, people with MS are more likely to have anxiety if they:

• Are female
• Were diagnosed at a younger age
• Have a history of depression
• Have less severe disability

For people with MS, anxiety also may stem from the stress of adapting to a new and unpredictable diagnosis.

Talk to Your Doctor

Many movement disorders and neurologic diseases can have symptoms similar to MS or SPS. If you have symptoms that concern you, talk to your healthcare provider. Your doctor or a neurologist can recommend tests to help figure out what’s causing your symptoms.

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