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How to recognize sinus tracts, keratinous cysts


In part three of the discussion on isotretinoin, our experts discuss distinguishing sinus tracts or keratinous cysts from nodular areas of inflammation and techniques for treating via intralesional injection.

Dermatology Times editorial advisor, Dr. Elaine Siegfried continues her discussion with Jim Leyden, M.D., emeritus professor of dermatology at the University of Pennsylvania about the art and science of isotretinoin therapy. In part three, the two discuss distinguishing sinus tracts or keratinous cysts from nodular areas of inflammation and techniques for treating via intralesional injection.

Elaine Siegfried, M.D. Dr. Siegfried: A patient I saw recently had a history that was similar to this description: whatever that granulation tissue reaction is. She had horrendous crescentic bilateral scars on her cheeks. At those particular places, after she got this granulation tissue response, she had been treated with intralesional corticosteroids. All the time she was on 100 mg of isotretinoin a day. I debrided those wounds - they were really very unusual, funky flaps of skin - and the biopsy came back as epidermoid cyst. She had sinus tracts that had developed.

Recommended: Isotretinoin’s discovery and development

She only had intralesional corticosteroids at these very persistent horrendous scars, and she had cystic acne in other places. But my gut feeling is that intralesional corticosteroids somehow might contribute to that.

In the very early days of isotretinoin, intralesional corticosteroids were a much more frequently used treatment, and I think that that particular complication of this sinus tract happened more back in those days. What are your thoughts?

Jim Leyden, M.D.Dr. Leyden: You can overdo intralesional steroids, but the first question is identifying the patient who has sinus tracts. This can be tricky. I have had patients referred to me who have failed isotretinoin, and what they have are sinus tract lesions that usually do not respond very well. Sinus tracts tend to be linear as opposed to circular, nodular lesions; they often have an angulation to them. Once you learn how to recognize them, then it is very easy to spot them. They tend to be in individuals who have other sinus tract disease or who have family members with sinus tract disease, like what we call hidradenitis or pilonidal sinus or occasionally sinus tract disease on the scalp.

LISTEN: Isotretinoin audio recordings

With acne you get a lot of disruption of sebaceous follicle epithelia. These patients have a tendency for epithelial repair response - to have epithelial buds migrate through the dermis and produce these linear serpentine epithelial tracts - which can become recurrently inflamed. Just like hidradenitis does not respond to isotretinoin, those types of lesions do not respond to isotretinoin treatment either.

I think intralesional steroids are very useful for sinus tracts, but if they are persistent and you just can’t get the inflammation to subside, then they actually have to be surgically removed.

NEXT: Karatinous cysts


Keratinous cysts

Dr. Siegfried: So how does that differ from the eruptive keratin cysts that happen with isotretinoin?

Dr. Leyden: You can have keratinous cysts as part of the attempt to heal disrupted follicular epithelium that occurs in acne. Occasionally with the higher doses of 1 mg/kg, you can get eruptive keratinous cysts. A keratinous cyst is another imperfect healing.

Recommended: Isotretinoin dosing decisions

You can recognize them in a couple of ways. First of all, these areas are constantly recurring areas of inflammation in the exact same spot. If you suspect it clinically or you hear that history, feel around the obvious area of inflammation under the surface. You can feel the rest of the lesion as something you can define and get your fingers around. They can occur eruptively with the 1 mg/kg dose.

Dr. Siegfried: That reminds me of John Strauss' teaching when I was an early resident. He actually palpated everyone's acne and sometimes with teenagers they are mortified when that happens. But it was an incredible, valuable clinical tool and you can learn a lot by feeling it as well as looking at it. He couldn’t really judge cystic acne alone without palpating it.

Leyden: I could not agree more. Hoffmann-La Roche had a new formulation of isotretinoin that got approved by the FDA and then they decided not to market it because the FDA wanted a phase IV study that would have taken three generations of dermatologists to be involved in. They were concerned about, for one thing, whether or not ideation of suicide could be induced by the drug. But I looked at the baseline photographs of all the people in the study and I identified 37 patients who had lesions that I said would not go away with the drug, because I thought they were either a sinus tract or keratinous cyst, and I was right with 37 out of 37.

LISTEN: Isotretinoin audio recordings

Once you have learned to recognize these things clinically and to distinguish them from nodular areas of inflammation that you can’t get your hands around and feel, they’re pretty easy to recognize. But until you do, it is a little bit like listening to mitral murmurs; somebody can hear them, but you’re having trouble hearing them.

NEXT: Injection techniques


Injection techniques

Dr. Siegfried: When you recognize those patients, what do you do then?

Dr. Leyden: I think intralesional steroids are very useful for keratinous cysts if they are inflamed. Sometimes when you inject an inflamed keratinous cyst, the whole thing seems to melt, or enough of it melts that nothing more needs to be done. But if it’s constantly recurring, it has to be removed the same way the sinus tract lesion is. If it is persistent and doesn’t respond to intralesional steroid, I think then it should be removed.

Recommended: Isotretinoin’s discovery and development

Dr. Siegfried: So when you inject cysts, do you do it into the cyst cavity or in the periphery?

Dr. Leyden: I mostly put it into the cavity, because I think a lot of it diffuses. The question is: Could you do better by injecting the periphery? That’s an interesting question. I think one of the things that is most interesting about injecting steroids in the skin is if you get anywhere near the subcutaneous layer, significant atrophy can develop.  

Dr. Siegfried: But injecting into the cyst cavity has the potential to cause micro-rupture of the cyst resulting in terrible inflammation. If you inject around the cyst, then you get atrophy. How do you manage that?

ALSO READ: Should you wait after isotretinoin to treat acne with laser?

Dr. Leyden: I us a 30-gauge needle - and my general rule is, depending on the size, no more than 1 mg to 3 mg of steroid. I do not believe in injecting until it blanches. Once you see blanching, that’s a sign of increased pressure, and that’s usually when it hurts and may rupture. I think it is the amount you want to put in that is important, not the volume. You figure out how to put in 1 mg, but you could put in 5 cc if you dilute it enough. I think if you have a 10 mg/mL syringe, then a 0.1 mL will have 1 mg. And if you inject 0.2 mg into an inflamed keratinous cyst, you’re not going to get rupture of the cyst and it’s not going to hurt. This way, you put in the amount you want, but the volume is not big enough to cause blanching and distention and/or rupture of the cyst.

Dr. Siegfried: So that’s a good pearl. It is another area of constant and common-use treatment that all dermatologists are taught to do with such variation in technique and dose, and I think the outcomes can vary.

Dr. Leyden: Right from the time I started doing it, I noticed when patients started saying, “Boy, that hurts,” which always seemed to be just as it blanched. That’s when I started backtracking the volume and paying attention to amount and how often do I get an atrophy. That’s how I came to the 1 mg to 3 mg dose per cyst.

LISTEN: Isotretinoin audio recordings

Dr. Siegfried: You can try that with sinus tracts as well?

Dr. Leyden: For sure. Once you learn, if you take your time, you can actually get into the tract and you can get much more easily into the cyst. You can follow the epithelium, the actual sinus and inject it with a lot less discomfort.

Dr. Siegfried: That’s a great pearl. Thank you.

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