Study flags dye interference risk in fluorescence-guided node mapping

A new exploratory study in Animals suggests methylene blue can substantially suppress the near-infrared fluorescence signal of indocyanine green, potentially complicating sentinel lymph node mapping when the two dyes are used together in canine and feline oncology surgery. The authors evaluated methylene blue–indocyanine green mixtures across several imaging modalities and found evidence of fluorescence quenching, raising a practical caution for surgeons who rely on indocyanine green signal intensity during intraoperative mapping. That lands as veterinary teams are expanding use of fluorescence-guided lymphatic mapping, while methylene blue itself continues to draw interest in other areas of veterinary medicine because of its broader biologic effects and practicality in some settings. In a separate new Animals study in Nile tilapia, for example, methylene blue delivered in feed prevented mortality during acute nitrite intoxication, lowered methemoglobin concentrations, and was associated with less severe gill damage—an illustration of why the dye remains clinically attractive even as its optical interactions may complicate imaging workflows. A separate new JAVMA report also points to 10% fluorescein sodium as a feasible, low-cost option for intraoperative sentinel lymph node mapping in dogs, underscoring growing interest in alternatives that may be more accessible in cost-constrained settings. (pubmed.ncbi.nlm.nih.gov)

Why it matters: For veterinary professionals, the takeaway is less about abandoning dual-tracer workflows and more about understanding when dye combinations may reduce signal quality, alter node detection, or create false reassurance if fluorescence appears weak. Sentinel lymph node mapping is increasingly central to staging and surgical decision-making in dogs, and recent studies have explored methylene blue alone, indocyanine green near-infrared imaging, and combined pre- and intraoperative mapping approaches across mast cell tumors, thyroid carcinoma, mammary tumors, and other cancers. At the same time, methylene blue’s continued utility outside oncology—including its apparent ability to counter methemoglobinemia-related injury in fish exposed to nitrite—helps explain why clinicians may keep reaching for it as a familiar, versatile dye. If methylene blue interferes with indocyanine green under some conditions, protocol design, tracer sequence, dilution, and equipment choice may matter more than many teams assumed. (pubmed.ncbi.nlm.nih.gov)

What to watch: Watch for follow-up clinical studies testing whether the quenching seen in vitro translates into lower sentinel node detection rates in live veterinary patients, whether fluorescein sodium gains traction as a lower-cost workaround, and whether methylene blue protocols become more indication-specific as evidence grows across species and use cases. (pubmed.ncbi.nlm.nih.gov)