Compared with the nonparaneoplastic SPS, usually associated with glutamic acid decarboxylase 65 (GAD65) antibodies, patients with amphiphysin-related paraneoplastic SPS are older and frequently have neck and upper limb involvement.54 Although some patients with anti–GAD65-associated SPS may have cancer, a paraneoplastic etiology should not be considered unless GAD65 is found expressed by the tumor cells. This evidence concerns the gene AMPH and stiff-person syndrome.