Study flags methylene blue interference with ICG node mapping

A new exploratory study in Animals suggests methylene blue can substantially interfere with indocyanine green, or ICG, during near-infrared fluorescence imaging, raising a practical concern for veterinary teams that use both tracers during sentinel lymph node mapping in dogs and cats. The paper, by Elisa Maria Gariboldi, Luigi Auletta, and Roberta Ferrari, examined methylene blue–ICG mixtures across multiple near-infrared imaging modalities and found evidence consistent with fluorescence quenching, meaning the blue dye may dampen the green signal clinicians are relying on intraoperatively. That matters because combined visible dye and fluorescence protocols are increasingly used in veterinary oncology, especially as ICG-based sentinel lymph node mapping gains traction in canine cancer surgery. (veterinaryoncology.biomedcentral.com)

Why it matters: For veterinary professionals, the takeaway is simple: if methylene blue is used alongside ICG, a weak or absent fluorescent signal may not mean the node failed to drain, it may reflect tracer interference. That could affect node identification, staging accuracy, surgical confidence, and case workflow, particularly in practices adopting fluorescence-guided oncology with limited equipment flexibility. The issue lands as the field is also exploring lower-cost mapping alternatives, including a small 2026 JAVMA study in six dogs that found 10% fluorescein sodium identified sentinel lymph nodes in all cases without adverse events, underscoring broader interest in practical, accessible mapping options. (mdpi.com)

What to watch: Watch for follow-up clinical studies that test whether separating injection timing, changing dye ratios, or switching tracers can preserve mapping accuracy in real surgical cases. (pubmed.ncbi.nlm.nih.gov)