Managing superficial pyoderma with light therapy

This article is sponsored by Vetoquinol.

Superficial bacterial folliculitis, also called superficial pyoderma, is a commonly diagnosed dermatological condition in dogs.^1,2 These infections are secondary to primary conditions affecting normal skin barrier function (eg, allergic skin disease, trauma, burns), keratinization (eg, nutritional deficiency, liver disease), and immune regulation (eg, neoplasia, autoimmunity, endocrinopathy).² Cats less commonly develop superficial pyoderma perhaps because of decreased adhesion of staphylococci to feline corneocytes, but the primary issues causing infection are similar to those seen in dogs.^3-8

The primary pathogen associated with superficial pyoderma in dogs and cats is a normal resident of the skin, Staphylococcus pseudintermedius, but other flora may be involved.^2,8-12 As the normal homeostasis of this organism is disrupted from a primary disease, these gram-positive cocci invade deeper regions of the epidermis and hair follicle epithelium, increase in number, and enhance inflammation.

Classical clinical lesions of superficial pyoderma include papules and pustules that may eventually progress to alopecia, epidermal collarettes, scales, and crusts. Often the skin is erythematous and pruritic. Chronic cases may demonstrate lichenification, hyperpigmentation, and scarring alopecia from long-standing inflammation and infection.² Cats may develop even more unique cutaneous reaction patterns and skin lesions—especially when allergic skin disease is present—including miliary dermatitis, eosinophilic plaques, rodent ulcers, and eosinophilic granulomas.⁵

Identifying and addressing the primary disease is paramount in achieving complete, permanent resolution of the superficial pyoderma. Therefore, treatment is multifactorial and aimed at addressing the primary disease, reducing skin inflammation, and treating the infection directly. Current guidelines for the treatment of superficial pyoderma in dogs recommend the use of topical antimicrobials as sole therapy whenever possible; however, overuse of systemic antibiotics remains common.^2,13-16

Topical therapy has many benefits including direct antimicrobial effects without use of an antibiotic, reduction in antibiotic-resistant bacterial populations, restoration of the normal skin barrier, enhancement of skin hydration, physical removal of keratinous debris, and removal of offending allergens from the haircoat.^2,14 However, topical therapy is met with challenges that impede clinical application. Adherence is the biggest concern when recommending topical therapy to pet owners. Frequent bathing or application of medicated solutions to the skin can be difficult when busy owner lifestyles combine with a nonadherent patient. Skin inflammation can be painful and animals may be resistant to topical therapy. Cats are fastidious groomers and may lick away a medicated topical therapy before it can achieve appropriate contact time. Additionally, some topical agents can cause oral erosions and ulcerations or even gastrointestinal disturbance when groomed off. For these reasons, systemic antibiotics continue to be a common prescribing practice for superficial pyoderma.

All antibiotic use, despite duration or frequency, contributes to the development of antibiotic-resistant bacterial populations on the animal and in the environment.^17-19 From that very first dose, bacteria are constantly evolving to implement inherent and acquired resistance mechanisms necessary for survival. One well-recognized mechanism is oxacillin resistance through the mecA gene, which produces a penicillin-binding protein receptor with poor affinity for β-lactam antibiotics.^{2,14,15,20-23} Even more concerning than these oxacillin-resistant strains are those that develop multidrug resistance, which is defined as resistance to 3 or more antibiotic drug classes. This may happen over time with repeated antibiotic exposure or after a single dose of certain antibiotics such as fluorinated quinolones.^2,20,23-25 The continued emergence of antibiotic-resistant bacteria inhibits the successful treatment of bacterial infections in pets and humans. As veterinarians consider how their antibiotic use contributes to this growing pandemic, they must look for alternative, safe, effective, affordable, and convenient antibacterial treatment modalities.

Phovia as a solution

Investigation into the photobiological effects of light therapy has been ongoing for the past 50 years. Photobiomodulation (PBM) therapy is a type of light treatment that uses visible or near infrared light to promote therapeutic benefits including induction of tissue healing and regeneration and inhibition of biological responses that induce pain or inflammation. The treatment distance, wavelength, fluence, pulse parameters, spot size, and irradiation time influence the effects of light energy on tissue. Visible light with wavelengths ranging from 400 to 700 nm can stimulate positive photobiomodulatory effects that promote wound healing, reduce inflammation and pain, modulate stem cell populations, and reduce bacterial contamination of wounds.^26,27

Once visible light enters the skin, it is absorbed by the cells and initiates chemical changes dependent on the wavelength (or color) of light and the chromophore within the skin.²⁷ Within each cell, membrane-bound organelles called mitochondria contain chromophores that absorb the light energy and begin making energy (adenosine triphosphate; ATP) via activation of cytochrome c oxidase. Outcomes of the mitochondrial respiratory pathway activation include stimulation of secondary messenger pathways, production of transcription factors and growth factors, and increased ATP production. However, excessive light energy exposure will overstimulate mitochondrial respiration and cause expenditure of all ATP reserves, which creates oxidative stress resulting in damaging elevations of nitric oxide, production of harmful free radicals, and activation of cytotoxic mitochondrial-signaling pathways leading to apoptosis.^27,28 This is why creating PBM therapy protocols is important for targeting the beneficial effects while avoiding unintended harm.

Specific benefits of light energy within the visible light spectrum can be broken down into each color of light. Blue light (400-500 nm) has a lower penetration depth and primarily interacts with keratinocytes, reduces bacterial adhesion and growth, and increases intracellular calcium and osteoblast differentiation.^29-31 Green light (495-570 nm) affects the superficial tissue and alters melanogenesis, reduces hyperpigmentation of the skin, and reduces tissue swelling.^29,30 Red light (600-750 nm) penetrates deeper into the dermis and subcutis where it acts on cellular mitochondria to reduce inflammation and promote collagen synthesis through fibroblast proliferation and production of transforming growth factor-β, fibroblast growth factor, platelet derived growth factor, and others.^26-28,32,33 Red light has proliferative effects on mesenchymal stem cells and induces proliferation of epithelial colony forming units important for tissue repair and regeneration.^34,35

Phovia, sold by Vetoquinol, is a form of fluorescent PBM therapy utilizing a blue light emitting diode (LED lamp, 400-460 nm) and topical photoconverter gel that emits low-energy fluorescent light (510-600 nm) when illuminated by the LED lamp.^36,37 This interaction results in the formation of multiple wavelengths of visible light, each with a unique depth of penetration and effect on the tissue as described above. Application is fast and simple. The affected skin may be clipped free of hair and cellular debris removed with gentle cleaning. The skin is allowed to dry before application of the photoconverter gel. Just prior to application, 1 ampule of fluorescence chromophore gel is added to 1 container of photoconverter carrier gel and mixed thoroughly. The mixture is applied in a 2-mm layer to the affected skin, and the LED lamp is held 5 cm above the lesion and used to illuminate the area for 2 minutes. The gel is wiped away using saline-soaked gauze. The application can be repeated immediately after 5 to 10 minutes of rest or a second application can occur a few days later. Twice-weekly applications are continued until the wound is healed. Appropriate eyewear is required to protect the operator from the intensely bright light. Application is pain free and stress free for the patient, so sedation is not typically required.

Benefits of Phovia

Phovia shows great promise as a safe, effective therapy for treatment of numerous inflammatory dermatoses in dogs including superficial pyoderma,³⁸ deep pyoderma,³⁹ perianal fistula,⁴⁰ interdigital dermatitis,⁴¹ calcinosis cutis,⁴² acute traumatic wounds,⁴³ chronic wounds,³⁷ surgical wounds,⁴⁴ and otitis externa.⁴⁵ Phovia as a sole therapy speeds time to healing by 36% in canine superficial pyoderma as compared with dogs receiving oral antibiotics alone.³⁸ In one study, dogs with superficial pyoderma were treated with Phovia alone or with an oral antibiotic alone. Dogs treated twice weekly with Phovia demonstrated complete clinical healing in about 2.3 weeks (P < .05)whereas dogs receiving oral antibiotic healed in about 3.75 weeks.³⁸ Additionally, Phovia speeds time to healing by nearly 50% in deep pyoderma when used with an oral antibiotic (5.7 weeks of treatment) compared with dogs receiving only oral antibiotic (11.7 weeks of treatment).³⁹ The ability of this fluorescent PBM therapy to eliminate or significantly reduce duration of exposure to antibiotics will decrease the spread of antibiotic-resistant bacterial strains within pets and humans.

Phovia’s high safety profile makes it a beneficial tool to implement in everyday practice. Training the veterinary team to communicate therapy benefits with clients as well as to perform treatments is fast and easy. Training the veterinary technicians to perform treatments will give the veterinarian time to examine other patients. A single back-to-back application takes about 15 minutes, so pet owners can be in and out of the clinic quickly; however, the 2 weekly treatments can be separated by a few days if the veterinarian prefers to evaluate the patient more frequently. Additionally, when used as a sole therapy, clients are not required to administer oral or topical medications at home. This greatly improves treatment adherence and success. Instruct clients to use once-daily smartphone photos to document improvement at home. This can be useful when deciding how many treatments to perform. Most cases of superficial pyoderma will resolve completely by the third treatment.³⁸ It is a good idea to communicate to clients that 3 to 4 weekly treatments may be required.

Conclusion

Phovia is a versatile, innovative therapeutic approach to numerous types of dermatitis.³⁶ It is easy to implement in general practice, and is safe, pain free, and affordable. Phovia is highly effective for superficial and deep skin infections and eliminates the need for clients to administer numerous at-home treatments. This greatly improves the pet-owner bond and treatment outcomes by promoting adherence. Phovia accelerates time to wound healing, which decreases duration of antibiotic exposure and may reduce risk of antibiotic resistance development in these cases.^2,13,36-39 Phovia’s efficacy against antibiotic-susceptible and antibiotic-resistant bacteria shows promise as an alternative therapeutic approach that promotes the principles of antimicrobial stewardship.³⁶ If you are interested in purchasing this medical device for your practice, contact your Vetoquinol service representative.

Amelia G. White, DVM, MS, DACVD is an associate clinical professor of dermatology at Auburn University College of Veterinary Medicine.

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