Test Details: Stiff person syndrome (SPS) is a rare neuroimmunologic disease. A variant of SPS has been recognized which is associated with autoantibodies against amphiphysin and possibly with breast cancer. Amphiphysin Ab coexpressed with other paraneoplastic antibodies are associated with neurologic disorders such as sensory neuropathy, autoimmune encephalitis and myelopathy. Amphiphysin Ab-associated SPS may require steroids, plasmapheresis, or cancer treatment.