Case Report: Breast cancer-associated paraneoplastic stiff person syndrome: anastrozole monotherapy insufficient for symptom improvement

Abstract

Stiff person syndrome (SPS) is a rare clinical disorder presenting with progressive muscle stiffness and painful spasms. Its ill-defined mechanism and variable presentation make diagnosis a challenge, though it is associated with a range of specific auto-antibodies. One particular antibody, anti-amphiphysin, is found in the presence of breast or lung malignancy and leads to a disorder termed paraneoplastic SPS (PSPS). Our patient, an 83-year-old woman, presented with bilateral leg weakness, spasms, and left clubfoot over a period of three months. She also reported a lump in her left breast for which she had not sought treatment over the past 10 years. Her ankle radiograph was negative for fractures and dislocations, while an MRI of the left leg was negative for plexopathies. Electromyography was suggestive of an SPS disorder and a positive anti-amphiphysin test indicated a diagnosis of PSPS. Her symptoms were managed with baclofen, diazepam, and five cycles of therapeutic plasma exchange (TPEX) over 10 days. Breast imaging revealed a 4.5-cm left breast lesion, later biopsy-confirmed as invasive ductal carcinoma (ER+, PR+, HER2−). The patient declined definitive surgical management, opting instead for once-daily anastrozole 1 mg as hormonal therapy. This regimen was not sufficient to lead to symptomatic improvement over a period of more than 30 days, and the patient expired less than 45 days after discharge. To our knowledge, this is the first case of PSPS to be treated in this manner. Our report illustrates that conservative management with anastrozole monotherapy was not sufficient to lead to symptomatic improvement in this form of paraneoplastic syndrome, suggesting the need for more aggressive pharmacological or definitive surgical intervention in order to produce symptom improvement and/or resolution.