What Is Stiff Person Syndrome (SPS)?

Stiff Person Syndrome (SPS) is a rare autoimmune neurological condition in which the immune system mistakenly attacks parts of the nervous system.

Classic SPS typically causes:

  • Persistent muscle stiffness, often in the trunk and legs

  • Painful muscle spasms

  • Heightened startle response

  • Difficulty walking

  • Increased muscle tone

Symptoms often develop gradually. Many people with classic SPS have anti-GAD antibodies, although not everyone does. In its classic form, SPS can be serious but usually progresses relatively slowly.

What Is PERM?

Progressive Encephalomyelitis with Rigidity and Myoclonus (PERM) is considered a more severe form within the SPS spectrum, sometimes described as stiff-person-plus syndrome.

Breaking down the name:

  • Progressive – symptoms worsen over time

  • Encephalo- – involvement of the brain

  • Myelitis – involvement of the spinal cord

  • Rigidity – severe stiffness

  • Myoclonus – sudden muscle jerks

PERM can involve:

  • Severe whole-body stiffness and repeated spasms

  • Brainstem symptoms

  • Difficulties with swallowing or speech

  • Abnormal heart rate or breathing

  • Autonomic instability

  • Risk of life-threatening complications

PERM is often associated with anti-glycine receptor antibodies, although not in every case.

How Are SPS and PERM Different?

Classic SPS mainly affects muscle tone and stiffness.

PERM involves additional brainstem and autonomic nervous system issues, which can affect breathing, heart rhythm, blood pressure, swallowing, and sometimes consciousness. It tends to progress more quickly and can become critical without prompt treatment and specialist management.