Study flags methylene blue interference in ICG node mapping
CURRENT BRIEF VERSION: A new exploratory study in Animals suggests methylene blue can suppress the near-infrared fluorescence signal of indocyanine green, a pairing commonly used during sentinel lymph node mapping in veterinary oncology. The authors tested methylene blue–indocyanine green mixtures at different ratios across three imaging modalities and found evidence of fluorescence quenching, raising concerns that combining the dyes may make indocyanine green-guided mapping less reliable than expected. That matters because indocyanine green near-infrared fluorescence imaging is gaining traction in dogs and cats as clinicians look for more precise, less invasive ways to identify sentinel nodes during cancer surgery. (researchgate.net)
Why it matters: For veterinary teams using dual-tracer protocols, the study is a reminder that tracer compatibility matters as much as tracer choice. Prior veterinary work has already shown stronger fluorescence intensity with indocyanine green alone than with indocyanine green plus methylene blue in a simulated feline tumor model, while recent reviews note that near-infrared mapping protocols still lack standardization across species and tumor types. In parallel, a new JAVMA report found that intradermal peritumoral 10% fluorescein sodium diluted 1:120 allowed sentinel lymph node identification in all 6 dogs studied, with lymphatic tracts visualized in 5 of 6, fluorescence appearing in about 8 minutes on average, and no adverse events observed. That practical blue/black-light approach also detected metastatic mast cell disease in several mapped nodes, supporting fluorescein sodium as a potentially useful lower-cost option where near-infrared equipment or indocyanine green workflows are harder to support. (pubmed.ncbi.nlm.nih.gov)
What to watch: Expect follow-up work in live canine and feline oncology patients to test whether teams should separate methylene blue and indocyanine green use, revise injection protocols, or consider lower-cost alternatives such as fluorescein-based mapping. Outside oncology, methylene blue is also drawing attention in other animal health settings: a separate Animals study reported that methylene blue–enriched feed prevented mortality and reduced methemoglobinemia during acute nitrite intoxication in Nile tilapia, highlighting the dye’s broader physiologic activity and the importance of matching its use to the clinical context. (research.vetmed.ufl.edu)