Mystery Case: Cowden syndrome presenting with paraneoplastic encephalitis

Abstract

A 64-year-old man complained of progressive memory loss for 12 days. Neurologic examination indicated moderate cognitive decline. Autoimmune antibody testing showed that both AMPAR and NMDA receptor (NMDAR) antibodies were positive in serum and CSF. Paraneoplastic encephalitis was diagnosed initially. Further evaluations confirmed 2 malignant tumors including lung small cell carcinoma, renal clear cell carcinoma, and multiple benign tumors including abdominal wall hamartoma, colon adenoma with severe atypical hyperplasia, and multiple cysts in liver and kidney. Further physical examination showed macrocephaly and multiple mucocutaneous lesions including acrokeratosis, fissured tongue, and mucocutaneous papillomatosis around his gingiva and neck (figure). Whole-exome sequencing test via next-generation sequencing identified a pathogenic heterozygous mutation c.438delC in the KLLN gene. Cowden syndrome (CS) was diagnosed.