Stiff-person syndrome (SPS)

Stiff-person syndrome is a rare disorder of the central nervous system that causes progressive muscle rigidity and painful spasms, usually starting in the trunk and the muscles close to it. Most people with the classic form carry very high levels of antibodies against GAD65, an enzyme the body needs to make GABA, a calming signal in the nervous system, and researchers believe impaired GABA signaling leaves muscles overexcitable. A smaller share of cases are paraneoplastic, linked to an underlying cancer and antibodies such as amphiphysin. It is associated with other autoimmune conditions and can occur alongside type 1 diabetes.

Stiff-person syndrome is considered rare, and research describes it as affecting roughly two-thirds women among autoimmune and paraneoplastic cases, with the paraneoplastic form most often tied to breast or lung cancer.

Common signs

Stiffness and rigidity in the back, abdomen, and limbs, sudden painful muscle spasms that can be set off by noise, touch, or stress, a tendency to startle, difficulty walking, and anxiety that often surrounds the unpredictable spasms.

This is a plain-language summary for orientation, not a diagnosis. Mechanisms are described as current understanding, not settled fact. Work with your own clinician for your care.