Anti-amphiphysin positive stiff-person syndrome due to invasive ductal carcinoma in a male patient

Stiff-person syndrome (SPS) is a rare progressive neurological disorder characterised by painful muscle spasms and progressive muscle rigidity, leading in some cases to impaired ambulation. Anti-amphiphysin positive SPS is a paraneoplastic variant, frequently associated with breast carcinomas and small cell lung cancers. We report the case of a 53-year-old patient who developed symptoms of anti-amphiphysin positive SPS 3 years before being diagnosed with invasive ductal carcinoma. Specifically, computed tomography (CT) of the chest, abdomen and pelvis, positron emission tomography-CT (PET-CT), mammogram, colonoscopy and magnetic resonance imaging (MRI) did not identify malignancy during the 3 years following the onset of symptoms. Following diagnosis of invasive ductal carcinoma and completion of curative-intent oncological treatment, the patient experienced improvement, though not complete resolution, in his SPS symptoms. This case highlights the importance of thorough oncological workup when clinical presentation and diagnostic testing are suggestive of anti-amphiphysin positive SPS.