RESUMO
Key Clinical Message: Stiff-Person Syndrome (SPS) can be associated with various malignancies, including lymphomas. Therefore, clinicians should always remain vigilant for the presence of an underlying malignancy, especially in older patients presenting with SPS. Abstract: Stiff-person syndrome (SPS) is a rare neurological disorder characterized by painful muscle spasms. It can occur as a paraneoplastic syndrome associated with various malignancies. We present a case of an older male adult with a history of recurrent fever episodes and elevated inflammatory markers for 1 year who subsequently developed neurological symptoms. The presence of positive amphiphysin antibodies led to the diagnosis of SPS, which prompted further investigations revealing an underlying Gray Zone lymphoma (GZL). This case highlights the challenges in diagnosing lymphoma and emphasizes the importance of considering SPS as a paraneoplastic syndrome in guiding toward the final diagnosis. The diagnostic challenge in our case is summarized in Chart 1.