Foot Problems - Interdigital Cysts and Growths and Pyoderma


Interdigital pyoderma and pododermatitis

Question: Dear Dr. Richards:

I have an 11-year-old shelty named Ben, whom the family love very much. He has a lesion on his right forepaw that seems to fit the description of "interdigital pyoderma" that you mentioned in a web-posted article involving a dog named Angie. I would deeply appreciate your advice on alternatives to surgery. His history may be summarized as follows.

About 2.5 years ago, I noticed that Ben had what appeared to be a small puncture between the outer two toes of his right forepaw at the juncture of the two toes and more towards the top of his paw than the bottom. The wound appeared neat as if made by the tip of an icepick. Ben walks regularly in a canyon that has plenty of foxtails that might have produced such an outwardly appearing puncture. After several weeks, the wound appeared to heal. But, with any daily walking of more than about a mile or so, it would re-open enough to bleed. He also walks with his right paw pidgeon-toed inward and with a slight limp that is more pronounced when walking down hill.

After several months, I took him to three different vets over the next year, none of whom knew what to make of the lesion, but all agreed that a foreign body should have worked itself out by that time. A fourth vet said that Ben had a tumor between his toes that had to be removed, so I okayed the surgery in February of 2001. This vet #4 said that the tumor was about a centimeter in diameter, but I personally was never able to feel it. Vet #4 removed as much tissue as possible without risking damage to the paw and toes. About two months later, the lesion returned between the adjacent pair of toes, and has subsequently spread very slowly up the paw (as may be seen in the attached images of 4/1/01 and 10/21/01).

The biopsy of the surgically removed tissue concluded the following. No evidence of malignant change in the tissue, but rather inflammatory and not neoplastic. Such a tissue reaction can be due to foreign body penetration or deep-seated chronic bacterial infection. Fragments of keratin appeared to be acting as foreign bodies, suggesting that rupture of a follicle may have released material which incited a focus of foreign body reaction. Neutrophila were seen mingled with macrophage-type cells, with neovascularity and granulation tissue formation seen in surrounding tissue. In short, the diagnosis was "focal pyogranulomatous inflammation, with secondary granulation tissue and tract formation."

I next took Ben to a 5th vet this past July who diagnosed the lesion as "interdigital granuloma" and had me give Ben a 30-day prescription of Baytril, along with regular Epsom Salts soaking of the paw. The lesion got a little bit better, but never went away, and is now much worse as shown in the attached image of 10/21/01. Ben also has periodic dark skin bumps that itch a great deal and eventually fall off, only to be replaced by 3-4 more elsewhere on his body. He has also been getting occasional yeast infections in his left ear. But outside of these skin problems, his health is excellent according to all vets who have examined him. By the way, he gets two small daily feedings of Science Diet, a mix of half the "sensitive skin" formula and half the "lamb meal and rice" formula.

So what should I try next? You suggested NeoPredef (Rx) and some sort of systemic medication as a possible treatment for Angie. I want to avoid a second surgery for Ben, as it would have to take much of his right forepaw. Is there any way I can stop the growth and discomfort of Ben's lesion? I would be so very grateful if you could suggest some actions I might take. I cannot resist also showing you what a beautiful dog he is (third attached image).

Very sincerely, Charles

Answer: Charles-

There are several possible approaches to the sort of problem that you are having with Ben that might help. I do not practice in an area in which foxtails are found, so I have very little opportunity to see the wounds from these. We have seen around three dogs with foxtail problems after trips out West. These do seem to be capable of causing long term infections that don't stop until they are removed. However, since surgery has been done once this seems like less of a possibility. I'm just not sure that the continued presence of a foreign body can be ruled out and if there is one, surgery still might be the best option.

We do see a lot of dogs with pododermatitis and interdigital pyoderma who have persistent cystic sores between the toes that often open and drain, though. Over the years these have been extremely frustrating to treat successfully with any one approach. So the following is a list of things that have worked in at least a few dogs, with some notes about how we use them:

Mupirocin ointment (Bactoderm Rx). Actually, we just started using this ointment more frequently. We like it so far and it seems to be helping one of our chronic cases some -- but it is sort of early to be sure.

Metronidazole (Flagyl Rx) has worked wonders for two or three cases of interdigital cysts in our practice. We had one dog who had been to four or five vets prior to moving into our area and had been treated with everything else on our list. He responded within ten days to metronidazole and the cysts actually cleared up. They have returned a couple of times now but have continued to respond to metronidazole. Right now, this is our favorite treatment for resistant cases of this problem but we could just be on a lucky streak since other things have seemed to work well for a while in the past.

Doxycyline, like metronidazole, has worked well for a couple of dogs who did not respond to treatment with other antibiotics. These cases have been a little more sporadic for us but it still seems worth a try to us.

Fluoroquinolones (Baytril Rx, Dicural Rx, Orbax Rx, others) are the most commonly recommended antibiotics in the dermatology literature. These are broad spectrum antibiotics that generally penetrate tissue well. Even though your vet chose the antibiotic group to treat with that is usually considered best, sometimes fluoroquinolones just don't work.

Clindamycin (Antirobe Rx) is an antibiotic that has good activity against anerobic bacteria which seem to be involved in some cases of interdigital cysts. It is often used in combination with fluoroquinolones but can also be effective alone in some dogs.

Cephalexin ( Keflex Rx) is our general favorite antibiotic for skin disease, especially in older dogs. We are comfortable using it long term, which is often necessary to control skin infections. It seems to be among the safer of antibiotics, although no antibiotic is totally risk free. If there seems to be any response to cephalexin early in treatment we usually try it for at least three weeks. I like trimethoprim/sulfa combinations (Tribrissen Rx, Bactrim Rx, others) but am reluctant to use these in older dogs because the side effect we see most often is reduction in tear production and older dogs often have problems with tear production as it is.

A bacterial culture and antibiotic sensitivity testing might be helpful in choosing an antibiotic but our experience with this has not been overly encouraging. We get a lot of staph bacterial growth, usually sensitive to most antibiotics we use even in infections that haven't responded to a couple of the antibiotics -- so we figure that we aren't really growing the organism causing the problem most of the time.

So our basic approach is to start with cephalexin and then move on to the other medications on the list, except that we often use cephalexin and metronidazole together rather than withdrawing the cephalexin. We have been using the topical mupirocin as an additional therapy in the last few cases but don't have much feedback on it, yet. We use fluoroquinolones last, mostly based on expense but also because we like to have an antibiotic that we don't use much, too. That is just a practice quirk, though. It would be easy to argue that using them first might save money if they work best.

I hope that this helps you help Ben.

Mike Richards, DVM 11/11/2001

Interdigital cysts

Q: Dear Dr. Mike, I hope you can shed some light on this problem and perhaps have a few recommendations on how we can make Angies live more comfortable. About two months ago now, Angie, our 8 1/2 year old Rottie had a inter-digital cyst removed from one of her front paws. It had been bothering her for a long time, but our old vet never bothered investigating why she was limping so, and just dismissed it as arthritis. Only when we changed veterinarians was it discovered she had a cyst between her toes. When it was removed, her limping all but disappeared, we were so happy. Now, it seems so have come back. Once again, she is limping and occasionally there is drainage. When we spoke to the vet after her surgery, he did mention that it had been a big cyst, and that he may not have gotten all of it.

Our question is: If she was to have the surgery again, and he managed to remove all of it this time, would it still return? What are the chances of that? Is there anything that we can do to make her more comfortable? Your advice would be GREATLY appreciated. Angie has been plagued by problems for all of her life, and has suffered greatly with food allergies, cruciate ligaments, hyperthyroidism, a blood clotting name it. We love her so, and want to do all that we can to make the rest of her years as comfortable as possible. Regards, Alena

A: It would be hard to tell you the potential for return of this cyst after surgery without knowing what kind of cyst it was and without knowing if your vet is like many practitioners who use the word "cyst" to describe many lots of skin problems, only a few of which are real cysts. I can give some general advice on problems of the feet and hopefully that will help.

One of the most common foot problems is interdigital pyoderma -- infections between the toes. Unless the underlying infection can be controlled, there is a strong likelihood of return of the cyst or development of a similar cyst in another location on the feet. Allergies and immune mediated disease can be the initiating causes of interdigital pyoderma. Often, if this is the case, there will be other skin disease or chronic ear infections in conjunction with the foot problems. If Demodectic mange mites are present they can cause severe secondary bacterial foot infections as well. Whatever the cause, when these infections get bad, lumps form that look a lot like cysts but are actually granulomas (solid lumps). Since most clients recognize the term cyst and few recognize the term granuloma, vets tend to mislabel these as cysts for convenience sake.

Some cancers can resemble cysts when they occur on the feet, as well. The most notable of these are probably melanomas which seem to occur on toes pretty frequently. It is hard to prevent recurrence of these without amputation of the toe or even the leg. These are clearly not cysts when examined after removal.

Real cysts are usually follicular cysts or sebaceous gland cysts (epidermoid cysts) in most dogs. These are benign cysts and complete removal should eliminate them. Dogs that are prone to cyst formation, especially epidermoid cysts, tend to get more than one of them, though. It is highly likely that a cyst will develop somewhere else if this was the type of cyst present. It is not always necessary to remove epidermoid cysts but they are prone to rupturing or becoming inflamed and painful.

If you elect to have surgery again, consider asking your vet to have a pathologist examine the tissue removed to determine what type of cyst is present and to confirm that the problem is cyst formation and not a "look-alike" problem like a granuloma or cancer.

Mike Richards, DVM

Interdigital cysts Part2

Q: Hi, Thanks SO MUCH for your reply! You really have shed a lot of light on the problem. I will get on the phone first thing tomorrow and speak with the surgeon. Angie has had food allergies (to meat, protein, brewers yeast, you name it all of her life) and it is very interesting that you mention allergies. Also, she has had recurrent ear infections! Never, did I realize there could be a connection! Also, before the surgery, the cyst would occasionally "weep" pus, and then seemingly heal up again. That was why we thought that perhaps she had something "embedded" in her paw that was coming to the surface. Is a granuloma cancerous? Is there any ointment that can be applied to the area? If you can't answer my questions because you are too busy, I understand. I just wanted to thank you, you were a great help! Alena

A: Alena- A granuloma is a mass that is formed around an irritation to the body's defense mechanisms. It is an attempt to "wall off" an infection, foreign body or other irritation and it is not a form of cancer. If one is lucky enough to remove the offending irritant with the granuloma there usually won't be a recurrence.

I haven't had much luck with ointments when treating interdigital pyoderma and other weepy foot conditions but I have had some luck using a cortisone/antibiotic powder, NeoPredef (Rx). The drying action of the powder seems to help some. In general it is necessary to use some sort of systemic medication (oral or injectable medication that affects the whole body) to control these types of problems.

Mike Richards, DVM

Interdigital Pyoderma

Q: I have a westie who develops recurrent cysts between his front paws. Our local vet pokes him full of steroids and antibiotics but they only recur so that he is seldom free from them. They are quite sore and do affect him. He is 11 years old and quite game for daily long walks, is not overweight but is stocky. Our local vet is happy with him and feels that he ought to live with the problem and just seek aid when it flares up badly. 25 years ago we had the same problem with a Jack Russell who became reluctant to exercise and became somewhat overweight ultimately causing his death. I hope that in 25 years some progress may have occurred. I do appreciate your availability on the net. I do the same as a dentist and feel; that I am being useful as I am sure do you. I hope you can help.

A: Westies are extraordinarily difficult patients when it comes to skin disease. I can understand why your vet is content with intermittent success in repressing the clinical signs. Sometimes it is hard to achieve that level of success in dealing with problems like interdigital pyoderma in Westies. On the other hand, he is likely to live a long time and I can understand your desire for a long term solution to the problem. My best advice would be to seek the help of a veterinary dermatologist if one is available in your area. Most of the time, the problem with Westies is allergic in nature. They are very prone to atopy and more prone than most breeds to food allergies. Allergy testing and hyposensitization will help many dogs with atopy. Food trials and hypoallergenic diets help with the food allergies. Intradermal skin testing still seems to be the best method of determining what a dog is allergic to for inhalant allergies (atopy) and dermatologists are the most experienced at this sort of testing in most areas. If you do not have a veterinary dermatologist available or do not think that you would be willing to do hyposensitization (usually you have to give the allergen injections yourself due to the schedule), then you may have to accept the current status. Your vet probably is doing pretty well even though it is frustrating. It does seem like we should have a better solution after all these years. I wish it were so!

Mike Richards, DVM


Michael Richards, D.V.M. co-owns a small animal general veterinary practice in rural tidewater Virginia. Dr. Richards graduated from Iowa State University's College of Veterinary Medicine in 1979, and has been in private practice ever since. Dr. Richards has been the director of the PetCare Forum...