Visiting Vet: Genghis’ ear mystery solved

Ear margin dermatosis, a disorder of unknown cause that affects the edges of the ears.

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Genghis is a handsome, playful, 1-year-old boxer pup who recently came in to have his ears checked. “He’s scratching them a lot,” his owner reported. The typical cause for itchy ears in dogs is otitis externa, an infection of the outer ear canal. Underlying issues such as ear mites or allergies may contribute, but bacterial and yeast infections are common. I flipped up Genghis’ right ear flap (technically called the pinna) and looked into the external canal. Pretty clean. “His left bothers him more,” his owner said. I walked around the other side and flipped up his left pinna. A little debris, but minimal. The canal did not look red or inflamed. I tried to look further down with my otoscope, but Genghis objected. I couldn’t rule out infection deeper in the ear, but if there was, I couldn’t see it, and nothing came out when I swabbed inside.

Just the day before I had seen a cat named Charlie. His owner was concerned kitty was scratching his ears. It wasn’t the first time I had checked Charlie’s ears. This particular visit they looked perfect. Clean as a whistle, right down to the eardrum. No evidence of fleas, so we could rule out flea bite allergic dermatitis. No scabs or skin eruptions in front of the ears, as we sometimes see in cats with allergies. Charlie lived totally indoors, so that eliminated mosquito bite hypersensitivity (which usually occurs on the nose, anyway, not the ears). I wrestled internally for a moment. Clients like a diagnosis. An explanation. An answer. A treatment. “I think Charlie is fine,” I said. “Everybody scratches sometimes.” Then I sat back and waited for an objection or request for medication. But Charlie’s owner was eminently rational. “Oh, good,” she replied. “I just wanted to be sure he was OK.” 

What about Genghis? Was his owner overreacting? Holding his ear in my hand, rubbing it absentmindedly, I pondered what to advise. Wait. What’s this? A two-inch linear area along the front pinnal margin that was dry and hairless. I pointed it out to the owner. “We just thought that was from roughhousing with his doggy friend,” she said. Now, my dog has a buddy who loves to bite her ears when they tussle, so this seemed a completely reasonable assumption, but the lesion didn’t look like a play bite injury. What about mange?

Sarcoptic mange is an itchy skin disease caused by Sarcoptes scabiei var. canis, a tiny mite that is highly contagious. Although related to the mite causing scabies in people, the variety affecting dogs can only live on humans for short periods. In people, an itchy rash occurs usually on arms, neck, and waist, but generally resolves spontaneously within three weeks, though reinfection can continue if the infected dog is not treated. Canine scabies can be carried by foxes, and rarely cats, but is usually contracted by contact with another infected dog. On dogs, the mites prefer ears, elbows, belly, and outer portion of the hocks. 

Whenever we see dogs with itchy ear margin lesions, we must rule out sarcoptic mange. This is not as easy as you might think. The first test is the “pinnal-pedal scratch reflex.” Sounds fancy, huh? All it means is we rub the end of the earflap and see if the dog starts scratching with its hind leg. Believe it or not, this is a pretty good test for sarcoptic mange. But Genghis did not scratch. I went on to the next test — a skin scraping. Using a scalpel blade, I scraped skin and debris from the suspicious area and examined it under the microscope, looking for mites or their eggs. Nada. Unfortunately, this does not completely rule out sarcoptic mange, as these mites are notoriously difficult to find. At this point, if we have a high index of suspicion, we often advise treating the dog with medication to kill mites. Even though we haven’t proven it’s mange, response to treatment basically confirms the diagnosis. 

But in Genghis’ case, I did not have a high index of suspicion. No one else was itchy. No history suspicious of exposure. Negative pinnal-pedal response. Reviewing his record, I saw that the same lesion on the left ear margin had been noted three months previously. I examined his ears again, and saw what I had failed to notice the first time. A similar lesion was starting on the front edge of the right ear too. Aha! This had to be one of those odd ear margin diseases. 

First is cutaneous vasculitis, an uncommon syndrome in which peripheral blood vessels become inflamed, leading to lesions on ears, lips, mouth, footpads, scrotum, and tail. It may be associated with underlying issues such as food hypersensitivity, infectious diseases, diabetes, or autoimmune disease. It is too complicated to discuss in full today. Since Genghis was young, otherwise healthy, and had no lesions other than those on his ears, I dismissed vasculitis. I believe Genghis has ear margin dermatosis, a disorder of unknown cause that affects the edges of the ears. Most commonly seen in dachshunds, any breed with pendulous ears may be affected. It often starts just with greasy dandruff forming along the ear margins, then may progress to hair loss, crusts, cracks, ulcers, even the formation of visible notches. Affected dogs often scratch and shake their heads. It is sometimes associated with hypothyroidism, and may be exacerbated by exposure to dry heat such as wood stoves, fireplaces, or forced hot air. Definitive diagnosis requires biopsy, but is often presumed based on clinical signs. 

There is no cure. Symptomatic treatment to try to control lesions may include topical shampoos and ointments, moisturizers, oral fatty acid supplements, and in severe cases, oral corticosteroids. Occasionally vitamin A or zinc supplements may be recommended. We started Genghis on oral fish oil and topical ointments. If his lesions don’t improve, we may add other supplements and additional topical treatments. At least his doggy playmate is exonerated. It’s ear margin dermatosis, not puppy love bites.