Stiff person syndrome (SPS) is a neurological disorder. However, it is also regarded as an autoimmune disease. Like other types of neurological disorders, SPS affects your brain and spinal cord (central nervous system).

SPS is rare, but can significantly affect your quality of life without proper treatment.

Most notably, SPS causes muscle stiffness. Early symptoms include:

  • limb stiffness
  • stiff muscles in the trunk
  • posture problems from a rigid spinal cord (this can cause you to hunch over)
  • spasms
  • walking difficulties
  • sensory issues, such as sensitivity to light, noise, and sound
  • excessive sweating (hyperhidrosis)
  • panic attacks

People with SPS may also have depression or anxiety. This may be caused by other symptoms you might be experiencing, or a decrease in neurotransmitters in the brain. The risk for emotional distress can increase as SPS progresses.

In the later stages, you may experience increased muscle stiffness and rigidity. This can cause falls while walking and standing. Muscle stiffness can also spread to other parts of your body, such as your face.

Some people with SPS may be at an increased risk of developing cancers of the breasts, colon, and lungs. This is due to the presence of amphiphysin antibodies.

The exact cause of SPS is unknown. It’s possibly genetic.

You may also be at an increased risk for developing the syndrome if you or someone in your family has another type of autoimmune disease. These include:

For unknown reasons, autoimmune diseases attack healthy tissues in the body. With SPS, tissues in the brain and spinal cord are affected, which causes symptoms based on the tissue that’s attacked. SPS creates antibodies that attack proteins in brain neurons that control muscle movements — these are called glutamic acid decarboxylase (GAD).

The average age of onset occurs in adults ages 30 to 60. It’s also twice as prevalent in women compared to men.

To diagnose SPS, your doctor will look at your medical history and perform a physical exam.

Testing is also essential. First, a blood test may be administered to detect GAD antibodies. While not everyone with SPS has these antibodies, up to 80 percent do. Your doctor may order a screening test called an electromyography (EMG) to measure muscular electrical activity.

SPS is sometimes diagnosed concurrently with epilepsy and cerebral palsy. Sometimes its mistaken for other neurological disorders, such as multiple sclerosis (MS) and Parkinson’s disease.

There is no cure for SPS. Treatment involves managing symptoms. Treatment may also possibly stop the condition from getting worse. Muscle spasms and stiffness may be treated with one or more of the following:

  • baclofen (Lorazepam), an anxiety medication that helps the body relax
  • benzodiazepines, to alleviate spinal cord spasms
  • diazepam (Valium), an anxiety medication
  • gabapentin, a type of drug used for nerve pain and convulsions
  • muscle relaxers
  • pain medications
  • tiagabine, an anti-seizure medication

Some people with SPS have also experienced symptom relief with:

  • autologous stem cell transplants, a process where your own blood and bone marrow cells are collected and multiplied before transferring back to your body
  • intravenous immunoglobin, this substance can improve blood plasma and decrease the number of antibodies that attack healthy tissues to treat sensory sensitivity
  • plasmapheresis, a procedure in which your blood plasma is traded with new plasma to reduce the number of antibodies in the body

Antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) may help with associated depression and anxiety. Zoloft, Prozac, and Paxil are among the many brands your doctor might suggest. Deciding on the right brand often takes a trial and error process.

In addition to medications, your doctor may refer you to a physical therapist. While physical therapy can’t treat SPS alone, the exercises you go through may significantly help with your:

  • emotional well-being
  • gait
  • independence
  • pain
  • posture
  • overall day-to-day function
  • range of motion

Depending on the severity of your symptoms, your physical therapist will guide you through mobility and relaxation exercises. With your therapist’s recommendation, you may even be able to practice some movements at home under a loved one’s supervision.

There’s no cure for SPS. The overall outlook depends on how effective your treatment plan is. Some people respond well to medications and physical therapy. However, these measures don’t work for everyone.

People with this condition are prone to falls because of a lack of stability and reflexes. This can increase the risk for severe injuries, and even permanent disability.

In some cases, SPS can progress and spread to other areas of your body. It’s important to let your doctor know if you experience any new symptoms, or if you aren’t seeing any improvements.