摘要Paraneoplastic cerebellar degeneration (PCD) can occur in patients with underlying cancer, such as small cell lung cancer (SCLC). Anti-CV2/CRMP5 antibodies are well-established biomarkers of PCD associated with SCLC, but cannot be detected in most situations. Recently, next-generation sequencing has been a promising technology to discover cancer-driven mutations, which provide an alternative strategy to accomplish ultra-early diagnosis of those patients. Here, we report the case of a 75-year-old man diagnosed with SCLC, who primarily presented with anti-CV2/CRMP5 antibodies positive PCD. Eight high-frequency gene mutations (TSC2, DNMT1, CIC, FGF6, NSD1, TSHR, CRLF2, and EPPK1) were detected 7 months before diagnosis with no abnormalities of imaging or cerebrospinal fluid examination found initially. Therefore, this case suggests the possibility of detecting certain somatic mutations for the ultra-early diagnosis of patients presenting with PCD associated with SCLC.