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     Western blot analysis of CRMP5 expression in SH-SY5Y cell lysate.    

  
  

CRMP5 antibody, directed against collapsin response mediator protein 5 (CRMP5), is an onconeural antibody associated with paraneoplastic neurological syndromes (PNS). CRMP5. a 62-kDa cytoplasmic protein encoded by the *DPYSL5* gene, plays a role in axonal guidance, neuronal differentiation, and synaptic plasticity. First identified in the 1990s, CRMP5 antibodies are commonly detected in patients with underlying malignancies, particularly small-cell lung cancer (SCLC) and thymoma. These antibodies are part of a broader group of paraneoplastic antibodies linked to immune-mediated neurological dysfunction.

CRMP5 antibody-related syndromes often manifest as encephalomyelitis, cerebellar ataxia, optic neuritis, or peripheral neuropathy. Retinal involvement, such as cancer-associated retinopathy (CAR), is also reported. Unlike some paraneoplastic antibodies (e.g., anti-Hu), CRMP5 antibodies may co-occur with other antibodies (e.g., anti-Hu or anti-Ri), complicating clinical presentations. Diagnosis relies on antibody detection via indirect immunofluorescence or cell-based assays, often paired with cerebrospinal fluid analysis.

Treatment focuses on immunotherapy (e.g., corticosteroids, IVIG) and addressing the underlying malignancy. Prognosis varies, with early intervention improving outcomes. Research continues to clarify CRMP5's pathogenic role, though its presence remains a crucial biomarker for guiding cancer screening in PNS.