Anti-amphiphysin encephalitis: A case report and review of the literature

Abstract Autoimmune encephalitis is increasingly recognized as a cause of subacute neuropsychiatric and neurological syndromes. Among its paraneoplastic forms, anti-amphiphysin autoimmunity is rare and most often associated with limbic encephalitis or stiff-person syndrome, usually in the context of breast or small-cell lung carcinoma. We report a 63-year-old man who presented with camptocormia and abdominal dyskinesia, an unusual hyperkinetic movement disorder phenotype associated with anti-amphiphysin positivity, without evidence of malignancy. He responded favorably to immunotherapy. The literature, largely comprising case series and case reports, highlights that anti-amphiphysin encephalitis is most often observed in adults in their middle to later years. The clinical spectrum is broad and most frequently includes cognitive impairment and seizures, while stiffness, movement disorders, and dysautonomia are less commonly reported but are likely underrecognized. Approximately half to two-thirds of patients harbor an underlying tumor, most often breast or small-cell lung carcinoma. Treatment typically involves immunotherapy combined with oncologic management where relevant; however, responses vary and outcomes are often poor in tumor-associated cases. Our case expands the recognized phenotype of anti-amphiphysin encephalitis and underscores the need to consider this diagnosis even in atypical presentations. Long-term malignancy surveillance remains essential given the strong paraneoplastic association.