Topical indocyanine green antimicrobial photodynamic therapy for refractory feline chronic gingivostomatitis: a case report

Feline chronic gingivostomatitis (FCGS) is a painful and severe inflammatory mucosal disease in cats that presents significant challenges in treatment. This case study describes a novel approach for a cat with FCGS that was unresponsive to antibiotics, non-steroidal anti-inflammatory drugs, and dental extraction. The cat exhibited rapid improvement after undergoing oral indocyanine green (ICG)-mediated antimicrobial photodynamic therapy (aPDT); however, treatment was discontinued due to an episode of anaphylaxis. Subsequent oral aminolevulinic acid (ALA)-mediated aPDT proved ineffective over nine sessions. The cat was then treated with a topical approach using ICG-aPDT. ICG was prepared by dissolving 5 mg of powder in 3 mL of sterile water, which was applied to the oral gingiva, followed by irradiation with an 810 nm diode laser, delivering a total fluence of 16.8 J/cm² per session through the skin in two divided doses. The cat underwent biweekly aPDT, totaling 13 treatment sessions without any adverse events over four months. Gradual weight gain was observed from the first treatment. During the three-year follow-up, there was no recurrence of FCGS. This case report highlights the potential efficacy of topical ICG-aPDT as a treatment modality for FCGS.