Photodynamic effect of argon and diode laser on cholesteatoma cell cultures after intravital staining with absorption enhancers

Chronic epitympanic otitis media, or chronic suppurative osteitis, is a destructive form of chronic middle-ear inflammation. The therapy of choice is complete surgical removal of the squamous epithelium from the middle ear. It is often impossible to inspect all areas of the middle ear with the posterior canal wall intact. Not all recesses can be reliably monitored with the microscope, particularly in the area of the antrum and hypotympanum. Residual squamous epithelium here causes frequent recurrences following cholesteatoma surgery. This study examines the effect of argon and diode lasers on cholesteatoma tissue. The aim is to develop a laser treatment selectively directed against cholesteatoma cells that can be performed after cholesteatoma surgery to eliminate any residual squamous epithelium. Intraoperatively harvested monolayer-cultured cholesteatoma cells stained in vivo with various absorption enhancers served as the in vitro examination model. Argon (499 nm) and diode lasers (810 nm) were applied since their irradiation has an appropriate tissue penetration depth and is absorbed by various chromophores such as neutral red (475–500 nm), fluorescein (488 nm), and indocyanine green (790–810). Intracellular staining of cultured cells increased the optical density at the wavelength corresponding to the dye. Neutral red damaged 50–60% of cultured cells merely by intracellular accumulation at high concentrations. An additive cell destruction of about 30% was achieved by also applying argon laser irradiation. Fluorescein diacetate caused no appreciable stain-induced damage to cultured cholesteatoma cells. Argon laser irradiation destroyed up to 60% of the cultures. Indocyanine green resulted in only minor damage to cultured cells. The diode laser destroyed up to 60% of the irradiated cells. Selective staining of cholesteatoma cells was not achieved with any of the dyes examined. Thus, other stained tissue could be damaged. Staining and subsequent laser irradiation destroys up to 60% of cultured cholesteatoma cells. Unstained irradiated cells are not affected. Indocyanine green and fluorescein are nontoxic and may thus be used as absorption enhancers. The diode and argon lasers appear to be basically suitable. Cell staining is not selective, i.e., other tissues would also be stained and damaged. To avoid such unwanted damage, it would be desirable to couple the chromophore to a specific antibody that binds only to cholesteatoma cells.