Multiple sclerosis (MS) and stiff-person syndrome (SPS) are both autoimmune diseases affecting the nervous system. These conditions have several symptoms in common, such as muscle stiffness, muscle spasms (cramps or twitches), difficulty walking, and muscle pain, which can lead to a delay in getting an accurate diagnosis.

SPS, formerly called stiff man syndrome, is a rare disease caused by an abnormal immune response. This neurological disorder occurs in only 1 to 2 people per million. Doctors sometimes misdiagnose it as other autoimmune disorders besides MS as well, such as Parkinson’s disease and fibromyalgia.

There have been some cases in which people have developed MS and SPS at the same time. However, the chance of this happening is extremely low.

While MS and SPS share several similarities, they also differ in a number of ways. Here, we’ll discuss how to tell the difference between MS and SPS and learn a little more about stiff person syndrome.

1. SPS Doesn’t Cause Nerve Damage

MS and SPS are caused by different factors, which means some of their symptoms look and feel distinct.

In MS, the central nervous system is physically damaged by the immune system. These areas of damage, called lesions, form in the brain and spinal cord. They lead to various symptoms depending on where the lesions are located. Some people will experience numbness or tingling, while others might notice vision disturbances or movement difficulties. These symptoms are usually absent in SPS.

Health experts aren’t entirely sure how exactly SPS develops. However, it seems to be linked to antibodies (immune system protein) that block anti-glutamic acid decarboxylase enzymes called anti-GAD65 antibodies. During SPS development, the body typically makes a lot of these antibodies, which lowers the levels of a neurotransmitter (brain chemical) called gamma-aminobutyric acid (GABA).

GABA is responsible for blocking certain signals within the nervous system. When GABA levels drop too low, nerves can display excessive electrical activity and send too many signals to the muscles. This can cause the muscle spasms and stiffness seen in SPS. However, this process doesn’t cause nerve damage, which means that numbness and pins-and-needles feelings aren’t usually present in people with this condition.

2. SPS Doesn’t Directly Cause Muscle Weakness

The MS disease process can lead to muscle weakness. The damage that occurs in the brain and spine prevents nerves from effectively communicating with muscles, limiting strength and making movement difficult.

In SPS, the nerve signals that connect the muscles to the brain and spinal cord aren’t blocked like they are in MS. Therefore, people with SPS don’t directly experience muscle weakness. They may, however, have trouble moving normally due to muscle stiffness.

3. SPS Usually Doesn’t Affect Coordination

Most people with MS eventually experience ataxia (loss of muscle coordination) caused by nerve damage. People with the condition might be clumsier than normal, have difficulty walking or speaking, or develop a tremor.

People with SPS may also experience walking problems or frequent falls, but this is typically because of muscle spasms (incidences of muscles suddenly contracting or twitching) — coordination itself isn’t usually affected. Muscle stiffness can also reduce joint mobility and make certain movements uncomfortable or difficult for people living with SPS.

4. SPS Doesn’t Lead to Dizziness

In MS, dizziness, vertigo, and loss of balance caused by lesions in the brain are often some of the earliest symptoms. People with these symptoms may frequently fall or have trouble walking because their sense of equilibrium isn’t working correctly.

People with SPS can have difficulties with balance and are at higher risk of falling, but this is 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

Although very rare, breathing can become difficult for people with SPS if muscle spasms occur in the chest or diaphragm muscles. This may cause a person to suddenly stop breathing, which can be life-threatening. However, breathing symptoms in SPS usually only occur when the condition grows more severe.

MS can make breathing more difficult because it weakens the breathing muscles. This weakness may be mild when a person is first diagnosed with MS, then worsen over time. Breathing symptoms in MS are usually different from those that occur in SPS — people with MS may experience shortness of breath or feel that breathing seems exhausting due to the physical effort required.

6. SPS Can Cause Curvature of the Spine

Many people with SPS develop a strong inward curve in the lower spine, known as hyperlordosis, or swayback. This occurs when tightened muscles in the back and abdomen pull on the spine. Alternatively, some people with SPS develop a forward rounding or hunching of the upper back, known as kyphosis. Over time, these changes in the structure of the spine can cause spinal cord compression — a type of spinal cord injury that can cause pain, weakness, or numbness.

People with MS frequently have difficulties maintaining good posture due to muscle weakness. This is typically a very early symptom of the condition. Poor posture can cause balance problems, back pain, and falls, but it doesn’t directly change the structure of the spine. However, MS does increase the risk of developing scoliosis, a sideways bend of the spine.

7. MS and SPS Have Different Symptom Triggers

People with MS experience exacerbations — periods in which old symptoms worsen or new symptoms appear. Exacerbations, also known as flares or relapses, may be triggered by getting too hot, smoking, being pregnant, and experiencing fatigue. Stress may also impact MS exacerbations for some people, although research on whether stress can worsen MS is inconclusive.

In SPS, exposure to cold temperatures rather than hot temperatures can cause muscle spasms. Loud noises, physical touch, emotional stress, and sudden movements are also known to cause symptom flares in people with this rare disorder.

8. MS and SPS Can Occur With Different Disorders

Research in the Journal of General Internal Medicine shows that up to 80 percent of people with SPS have at least one comorbidity — a second condition that occurs at the same time. The most common comorbidities seen in people with SPS are type 1 diabetes, pernicious anemia, vitiligo, and autoimmune thyroid disease. People with SPS are also six to 11 times more likely to have a psychological condition, such as anxiety or depression, than people without the condition, according to research in the Journal of the Academy of Consultation-Liaison Psychiatry.

Individuals with MS have comorbidities as well, but it’s hard to know how common they are. Studies have reported a very wide range of comorbidities in those with MS. The most common co-occurring conditions include depression, anxiety, high blood pressure, high cholesterol levels, and lung disease.

9. SPS Can Make You Anxious Earlier On

Low levels of GABA in the brain are linked with high levels of anxiety and depression. Because GABA levels are decreased in people with SPS, it’s common for people with the condition to experience increased anxiety, caused by chemical changes in their brains. SPS is sometimes first misdiagnosed as a panic or anxiety disorder.

People with MS also frequently develop anxiety, but this commonly occurs after their diagnosis. About 43 percent of people with MS have an anxiety disorder, according to the Multiple Sclerosis Association of America. Researchers have found that females, younger people, individuals with a history of depression, and those with a lower level of disability are more likely to develop anxiety, according to research from Multiple Sclerosis and Related Disorders. In people with MS, anxiety is most often caused by the strain of adapting to a new and unpredictable diagnosis.

Talk to Your Doctor

Several movement disorders and neurologic diseases can mimic the symptoms of MS or SPS. If you have symptoms that concern you, bring them up with your health care provider. Your doctor or a neurologist can recommend tests that help determine the cause of your health issues.

Talk With Others Who Understand

MyMSTeam is the social network and online support group for people living with multiple sclerosis. On MyMSTeam, more than 199,000 members come together to ask questions, give advice, and share their stories with others who understand life with multiple sclerosis.

Do you have confusing symptoms that could be either SPS or MS? Share your experience in the comments below, or start a conversation by posting on your Activities page.