A RESOURCE FOR THE ASTUTE 30 l Veterinary Practice News l March 2013 TheEducationCenter PRACTITIONER VeterinaryPracticeNews.com A special advertising section

digital spaces, then the presence of follicular cysts is Recurrent interdigital draining tracts not very likely (Figure 9). In these cases other under- lying causes need to be considered. Typically dogs treated with CO laser ablation who have follicular cysts as the underlying cause will 2 fail to respond to appropriate antibiotic therapy until all the other underlying causes of these lesions have By David D. Duclos, DVM, Dipl. ACVD have been shown to manifest by the presence (Fig- been eliminated. For The Education Center ures 4-6) of comedones, alopecia, hyperkeratosis and If there is a suspicion of follicular cysts the clinician callus formation on the ventral interdigital spaces on can take biopsy samples from the ventral lesional skin to Introduction the opposite side of the dorsal draining tract. Most confirm the presence of follicular cysts (Figures 10, 11). Interdigital pododermatitis in dogs has many caus- often these lesions occur in the lateral interdigital 1-4 es , one of which is follicular cysts that repeatedly spaces of the front paws. CO2 Laser Treatment rupture and cause draining hemorrhagic tracts in the Above this area of comedones are multiple cysts which Surgical removal of the follicular cysts and the kerati- interdigital spaces of dogs. repeatedly rupture and cause a pyogranulomatous fistu- naceous foreign body material inside these cysts is the The clinical lesions include erythema, edema, nod- lous tract that migrates to the dorsal interdigital skin be- only way to get complete resolution of this disease. ules, hemorrhagic bulla (Figure 1), hemorrhagic drain- tween the digits in the interdigital paw webs (Figure 7). The CO2 laser allows the veterinarian to remove the ing tracts (Figure 2), ulcers and scarring (Figure 3), The dorsal lesions are the most clinically obvious cysts without causing unnecessary damage to the sur- most commonly in the lateral interdigital space be- and consist of hemorrhagic bulla (Figure 1), hemor- rounding normal structures. The laser surgical proce- tween digits IV and V. Treatment includes eliminating rhagic draining lesions (Figures 2, 8) and scarring dure involves using a wide (“paintbrush”) laser abla- specific etiologic agents when present; soaking the from repeated ruptures (Figure 3). These dorsal le- tion tip as seen in Figure 12. paws in antiseptic solutions; long term antibiotics; and sions are often misinterpreted to be the primary le- The procedure begins with the laser set to contin- surgical debridement. sion. Failure to recognize the ventral pathology leads uous wave (CW) mode at 15 to 30 watts. In the be- When follicular cysts are present, surgical removal of to a failure in therapy and a continuation of repeated ginning there is a lot of keratin in the thick callus or the tracts is important in order to achieve resolution of the episodes of draining lesions. hyperkeratosis (Figure 4, 5, 6) and the higher watt problem. The CO2 laser surgery is the most appropriate Frequently these lesions are thought to be a foreign setting is needed. Once the deeper layers are surgical modality because of its ability to provide excellent body reaction and the dorsal lesions often undergo sur- reached, the watt setting is lowered to allow slower accuracy and repeatability, excellent intra-operative hemo- gical probing, lancing and debridement, which results tissue ablation and visualization of important nor- stasis and reduced post-operative complications. in further scarring. Meanwhile the dog is maintained mal structures such as large arteries and veins and

The state-of-the-art CO2 laser from Aesculight is on long-term antibiotics, corticosteroids and other anti- the adjacent normal tissue. used at our clinic routinely for these types of soft tissue inflammatory drugs with no response. The follicular cysts are filled with a keratinaceous surgeries. Aesculight laser features flexible fiber wave- A classic scenario is that the dog has recurrent material which is lower in water content than the guide beam delivery with scalpel-like handpieces for draining lesions in the same interdigital space. Since surrounding normal tissue so these cysts are easily ultimate surgical accuracy and precision. such cysts originate from hair follicles, the removal of visualized. Also with digital pressure applied this the haired structures in the affected area is important keratinaceous material can be expressed from the Interdigital Pododermatitis Diagnosis in order to prevent new cysts in this area. cysts, making their visualization easier (Figure 13). Interdigital follicular cysts are a special subset of If the dog has interdigital hemorrhagic bulla and The CO2 laser does not penetrate very deep so the canine recurrent interdigital dermatitis lesions that draining lesions that occur randomly in various inter- veterinarian is able to remove very thin layers of tis- sue with each pass and Figure 1 Figure 2 Figure 3 this results in a very precise removal of the diseased tissue and al- lows the sparing of the normal tissue. When all the cysts are removed as the sur- gical procedure moves toward the dorsal sur- face, one or two pyo- granulomatous tracts will become visible (Fig- Figure 4 Figure 5 Figure 6 ure 14). These tracts communicate out onto the dorsal surface. It is not necessary to re- move skin from the dor- sal lesion other than just opening the tracts. When all the diseased cystic and pyogranulo- matous material is re- moved the wound is left open to heal by second Figure 8 Figure 9 intention (Figure 15).

Treatment Outcome The usual healing period is four to six weeks, during which the paw will need to be wrapped with a protec- tive bandage. Figure 7 In a study done by the EducationCenter March 2013 l Veterinary Practice News l 31

Figure 10 Figure 11 Figure 12 READMORE… 1. Duclos DD, Hargis AM, Hanley PW. Pathogenesis of canine interdigital palmar and plantar comedones and follicular cysts, and their response to laser surgery. Vet Dermatol 2008;19(3):134-141. 2. Gross, T. L. et al. “Interdigital Furunculosis.” Skin Diseases of the Dog and Cat Clinical and Histopathologic Diagnosis. Ames, IA: Blackwell Science Ltd, 2009. Figure 13 Figure 14 Figure 15 3. Scott, D. W, W. H Miller Jr, and C. E Griffin. “Bacterial Skin Diseases.” Muller and Kirk’s Small animal dermatology. 6th ed. Philadelphia: W.B. Saunders, 2001. 304-06. 4. Duclos DD, “Canine Pododermatitis” Clinical Dermatology – Veterinary Clinics of NA, Sm Anim. Practice, V43, No1, Jan 2013, DO Morris, RA Kennis Editors, Philadelphia, PA, Elsevier author in his clinic, follicular cysts in 28 dogs were re- costeroids and had long periods with normal paws David D. Duclos, DVM, Dipl. ACVD, is a small-animal moved by laser ablation. Sixty-three percent had complete between procedures. G practitioner in Lynnwood, Wash., where he is the resolution with no further recurrences, 34 percent needed owner and clinical dermatologist at the Animal Skin a second laser ablation procedure and 3 percent needed and Allergy Clinic. He completing a residency in vet- three or more procedures to get complete resolution. This Education Center article was underwritten by erinary dermatology at the University of Pennsylva- Even when repeated surgical procedures were Aesculight LLC of Woodinville, Wash., manufacturer nia. He currently also teaches dermatology to senior needed, the dogs were better between the proce- of the only American-made CO2 laser. veterinary students from various veterinary schools dures. They were not on continual antibiotic or corti- as externs at his clinic.

Circle No. 103 on Reader Service Card