Aslan, a middle-age German shepherd, had a serious problem. Over the past four months he had developed multiple deep, oozing sores under his tail. According to medical records from his regular veterinarians, it may have started with an infected anal gland, but the perianal lesions had become so extensive and severe that Aslan had needed to be sedated in order for them to examine and clean the area. A presumptive diagnosis was made of perianal fistulas. This is a chronic, progressive disease in which the perianal tissue becomes inflamed and ulcerated. Although it is an uncommon condition, the most frequently affected dogs are middle-age German shepherds like Aslan. Mild cases may just look like small, weepy holes dotting the perianal area, as if someone had poked all over with a big pin. But the syndrome can progress, causing massive areas of ulcerations and draining tracts. It is painful and can be very debilitating. Affected animals frequently exacerbate the problem by constant licking. Other symptoms may include holding the tail low (since it hurts to lift it), straining to defecate, constipation, incontinence, weight loss, and lethargy.
No one knows what causes perianal fistulas, though some type of autoimmune problem is suspected. It has also been suggested that food allergies may be a contributing factor. Diagnosis is usually based on physical examination, history, breed, and by ruling out other diseases such as cancer, and bacterial or fungal infections. When Aslan came to me, his owner was worried. He had been unable to get the big dog to take medications prescribed by his veterinarian, and he had been advised to consult a specialist to discuss possible surgery. He knew Aslan couldn’t go on as things were. He didn’t want him to suffer. But Aslan was getting on in years and had other difficulties, like arthritis. What would surgery entail? Was it expensive? Wasn’t there something else he could do?
“Let me call the specialist and get more information,” I suggested. I hadn’t seen a case of perianal fistulas in many years, but if you pull out a text that still sits on my bookshelf, copyright 1997, and look up “perianal fistula,” you will read the following: “Surgery is considered the most effective treatment. However, a tremendous amount of controversy exists as to which surgical method should be used, and none of the currently employed result in consistent resolution of the problem … The primary objective of surgery is the complete removal or destruction of diseased tissue while preserving normal function. Multiple procedures may be necessary for complete resolution.”
I called my go-to veterinary surgical specialist off-Island, but he was, big surprise, in surgery and couldn’t come to the phone. He passed along a message via his liaison, saying he now treated all cases of perianal fistulas medically and hadn’t needed to do surgery on one in probably 10 years. OK. Time for this old dog (meaning me) to get up to speed. Eschewing my old texts for that newfangled thing called the Internet, I read up on medical treatment of perianal fistulas, then had a sit-down with Aslan’s dad. The dog was still in too much pain for me to lift his tail. His owner was reluctant to have him anesthetized again. We had a presumptive diagnosis consistent with his symptoms, breed, and age. And we were at the point where we had to be considering euthanasia if we couldn’t heal his extensive, painful lesions.
“Nowadays the treatment of choice is an immunosuppressive drug called cyclosporine,” I explained. We discussed possible side effects, pros and cons. We spoke at length about how to get Aslan to take medication. “Liverwurst, cat food, peanut butter, ice cream, cream cheese …” I rattled off a long list of tempting foods that could hide a pill, or two or three. “I’m hoping after a few weeks’ treatment, he’ll be in less pain so I can get a good look at things,” I said. The owner took on the challenge, reliably medicating Aslan for a few weeks, but things weren’t getting better. I called the surgeon again. This time he was able to come to the phone. It seems we were using the right medication, but not in the optimum way. In recent years, internal medicine specialists have found that dogs metabolize cyclosporine very erratically, making it hard to dose effectively — but by combining it with a second medication, ketaconazole, one could more reliably achieve safe, therapeutic blood levels. I had used this combination for other diseases before, simply because it’s less expensive, but hadn’t known it was essential to add ketaconazole to get the best cyclosporine response. “If that doesn’t work, you may have the wrong diagnosis,” he concluded.
We added ketaconazole, but also made plans to confirm the diagnosis and rule out other diseases, like cancer, that might mimic perianal fistulas. The following week, we anesthetized Aslan, examined and cleaned the lesions, and took biopsy samples. Since Aslan had gotten better at taking pills, we also added antibiotics to his regime.
Here’s what the biopsy report said. “Chronic moderate diffuse lichenoid lymphoplasmacytic dermatitis.” That’s a lot of words. The pathologist went on to say that although the biopsy results ruled out cancer, it didn’t give us a definitive diagnosis. Instead it raised additional differentials. The pathologist thought the most likely diagnosis was mucocutaneous pyoderma, another disease of unknown etiology that affects German shepherds. It’s thought to be a combination of bacterial infection and possible autoimmune problems, and, like perianal fistulas, may have an allergy-related component. Treatment usually involves many months of targeted antibiotics. Another possibility was a rare manifestation of discoid lupus erythematosus. Also an autoimmune disease. Also affecting German shepherds. And the initial diagnosis of perianal fistulas was still on our list.
How do you treat a dog whose differential diagnosis includes three different diseases, all of unknown etiology? Different specialists are advising different protocols, but for now our plan is to continue the cyclosporine/ketaconazole combination, add long-term antibiotics based on culture and sensitivity testing, consider allergy testing and hypoallergenic food, modify that plan if needed … and pray Aslan gets better.