Section: CME Category: Infectious Disease

Onychomycosis: Scientific Diagnosis and Treatment

Steve McClain, MD

Steve A. McClain, MD reviews the diagnosis and treatment of onychomycosis. Dr McClain discusses the normal anatomy of the nail and analyzes the pathology behind the infection and how this relates to treatment. He also examines the types and sensitivity of the stains available for diagnosis.

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Goals and Objectives
  1. Review the anatomy of the normal nail
  2. Describe the pathology of the nail infection in onychomycosis
  3. List clinical criteria to make a diagnosis
  4. Identify types of stains and their sensitivity
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  • CPME (Credits: 0.75)

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    Release Date: 03/16/2018 Expiration Date: 12/31/2020

  • Author
  • Steve McClain, MD

    Adjunct Professor Dermatology and Emergency Medicine
    Stony Brook, LI

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    Steve McClain ,MD is the owner of McClain Laboratories.

  • Lecture Transcript
  • Male Speaker 1: Here, I had the pleasure of coming in from the airport last night with is Dr. Steve McClain who was extremely enlightening to me on his thoughts on some ulcerations and what role fungus might play in those things. Dr. McClain comes from the University of Missouri I believe. He’s on the faculty at SUNY which is State University of New York. His topic is onychomycosis, science of accurate clinical diagnosis, which is going to become very important to you as practitioners. When you go submit for debridement on mycotic nails, you better have documentation before Medicare comes down on your butt because you don’t. So in any event, from a scientific approach, would you please welcome Dr. Steve McClain?


    Steve McClain: Okay. In medical school, I would fall asleep the first lecture after lunch almost every afternoon. I hope the same does not fall to you. I’m a dermatopathologist, MD, and I wanted to stress to you that we are all one. In terms of these diseases, no one group has the market or the lion’s share of these. We are all physicians whether DO, DPM, MD, we’re all physicians, and we practice one medicine, all one. I changed the title. I’m sorry. Scientific Diagnosis and Treatment. I thought I better throw something in about treatment. I do have an academic appointment at the university at Stony Brook in dermatology and also in emergency medicine. The latter mostly relates to wound healing research. Well, the diagnosis is pretty obvious most of the time. What I’ve discovered is that the lab diagnosis is not so simple. To the podiatrist, you look at these nails, these debridement, and it’s pretty obvious. I actually invented a test for this. And sometimes it’s helpful to segment out a test. This particular test is called the cheese test. If it looks like stinky cheese, it’s fungal, until proven otherwise. In my opinion, might as well lay it out there, nail dystrophy is not a pathologic diagnosis. It’s a myth. It’s a false negative lab test. I’ll tell you how I got there. Does this look cheesy to you? This is a section of nail. Let’s see, do we have a pointer here? Section of nail and there’s a little faint touch of eosin on top and the blue is the Alcian blue on the bottom, you can see it’s irregular. But most of the center is dominated by this plastic-like material or cheese. These nails been soaked in 10% to 20% KOH for an hour and it’s still relatively impermeable, you wonder why the antifungals don’t go through? There’s this big plastic component in the center. And it’s why these nails are so hard. They’re abnormally hard because of highly cross-linked fungal polymers. I know you’re not hearing that from anyone else but it’s what I believe to be true. So we would call this cheese test positive in our lab. I’m going to start off talking a little bit about onychomycosis treatment. And the first stage or step in the treatment is to make the diagnosis. And as residents, once you make the diagnosis, don’t deviate from it until you have positive evidence to the contrary. The treatment then, it begins with something like debulking the nail or avulsing the nail. The dermatologists routinely use 40% urea to knock all that cheese stuff down and then they’ll treat with terfenadine. Suppressing fungal sacs in the nail bed. Women patients are frequently bothered by the notion of fungal sacs in the nail bed. I don’t know why but they really are bothered by that. And it’s what’s happening, the infection foments in the nail bed way down low. And we need to treat the base until normal, which may take a year, may take a year and a half until that nail grows out.


    The goal then is to achieve normal nail transparency, translucency, a thin nail. And the normal nail is much thinner than you might think. I actually measured more than a thousand of them within the past two years and I’ll present the data. And it should cut easily. Combine treatments whenever possible. You have to gang up on the fungus. The fungus evolutionarily is much older than we are. These infections have been around far longer than medical science gives it credit for. Whether you treat them systemically, topicals, here’s an example of Vicks VapoRub. I know it’s in the lay literature and so on but part of the reason it works is it has three antifungals. These are all plant oils, camphor, eucalyptus and menthol, combination therapy. Enhancing penetration of topicals, I’m going to spend a couple of minutes on because there are some new developments in enhancing the penetration of topicals. Heat. If you travel to Hong Kong or any tropical country, in the closets they have heaters. They raise the temperature of their closets to keep the fungal growth down. Some of our old time therapies, whether it be diathermy or hydrotherapy that involved heat, suppress fungal growth. And it’s still the principle by which laser and ultrasound work. Same thing for photodynamic therapy or the blue light therapy, you put in delta-aminolevulinic acid , ALA. Whether you’re treating a solar keratosis or a foot fungus, you paint this on and shine a blue light on it, okay? This is photoactivated inside the cells and it kills them. It works for solar keratosis and early form of squamous cell carcinoma and also for fungus. Okay. The diffusion enhancers for transungual delivery, I think this is a new and kind of fun development. This was just published last month, ciclopirox delivery into the human nail plate using novel lipid diffusion enhancers. They tested this in horse’s hooves at the University of California at San Francisco where Howard Maibach has been there for about 40 years, point out that Marc Selner here is a podiatrist and these two, Selner and Rosenthal, actually own a company. I’m not going to mention them by name. But they received the patent on their product. That’s about all I’m going to say about treatment. The first step though is to make the diagnosis. One can understand why these don’t penetrate very well because in the middle there is a cheesy yellow plastic material highly cross-linked polymer that’s of fungal origin, okay? It’s not a nail anymore, it’s a fungal pseudo nail, okay. The field of surgical pathology was invented by a surgeon, Billroth, okay? Many of the advances in ulcer care, nail care and so on have been made by combining the efforts of surgeons and pathologist. But Billroth was his own surgeon. And you can still bill for a KOH test in the office even today. Eosin is a pretty good stain for fungus. I didn’t know that until a couple of years ago but it stains the cheesy part, that same yellow part is pretty well-stained by eosin. PAS is a good stain for carbohydrate. It’s actually a chemical reaction. It stains specifically carbohydrate and so the red is all carbohydrate. And this may have been taught to you as being plasma, it’s not. These are little fungal breeding grounds right here, these are vertical columns, and around each one of them grow the hyphae. But the PAS by itself has a sensitivity and it’s about 50%. If you combine the PAS by adding an Alcian blue stain, the sensitivity goes up to more than 90%. So anything that’s red or purple or blue is fungal with the combination stain. Alcian blue is known as a mucin stain so the underside of the nail, the deeper portion stains preferentially with it. If we look at Aspergillus niger in a culture, I don’t know if you can see that, but you see this faint little rim around here, that little shining light, that’s a mucous layer that’s down at the base.


    Now if we look at this in a tissue section, the fungus naturally layers out in culture. That’s what fungi do when they grow. And the same thing happens in the nail bed infections. At the base, this blue part here is from the Alcian blue and you can see it’s riddled with hyphae. If we zoom in on it, I thought those where just hyphae and some bubbles but if you look at these you notice that there are some cross, these are septate immature hyphae but they’re only staining with Alcian blue, okay? So, the immature hyphae will stain with Alcian blue and not with PAS. Notice that the PAS is being laid down almost like on top of the railroad tracks and the center is the Alcian blue positive part and the carbohydrate is laid down on top of it. That’s what fungi do in culture. That’s part of what they do. Part of the reason we’re as good as we are today has to do with this Cuban-born dermatologist from Miami, Nardo Zaias. He still practices. And he wrote this paper in the Archives of Dermatology, 1972, and he described the discoloration, the presence of tinea pedis, the onycholysis or splitting and that the nail was thick. We know now it’s mainly nail bed that’s due to the thickening. But in the same paper, and this is a time when this is pre-Lamisil, when surgical excision for onychomycosis was done. Can you imagine that, taking off the entire nail unit surgically? Here is the proximal nail fold, matrix, nail bed, hyponychium and the nail plate. Notice the nail plate here. Most of this thickness is not due to the nail plate but this accumulation of nail bed cornified cells. So most of the infection, and in fact, if we look at the nail bed here’s the normal epidermis, the nail bed is hyperplastic. And this dark line above, that is part of the disease. So it’s an accumulation. The infection is centered in the nail bed. And so the treatment has to not only take care of this mass of fungus on top but also the infection in the nail bed epithelium. This is a great paper. Richard Scher, former president of the American Academy of Dermatology, there is Warren Joseph, Bryan Markinson, Dr. Armstrong, Roderick Hay, some really high level people wrote a paper on diagnosis and definition of cure. I’m going to stick to the diagnosis because I can be critical about this paper a little bit. Primary criteria is discoloration, yellow, white, orange, brown. Secondary criteria, tinea pedis, as they listed it down here, but onycholysis. The main problems I have are in these two parts and we’ll go over those. And the lab is relatively insensitive. That’s one of the big problems and one of the reasons why I say nail dystrophy is a myth. The false negatives are so high in both cultures and by either KOH exam or by H&E and PAS, histopathology that we let you down, frankly. The lab is letting you down or used to. Cheese test positive, anyone? It’s yellow, it’s white, it’s brown, it’s orange. The thing I would point out to you is that I didn’t appreciate that you can do a little bit of quantification on this. How much of this nail is infected? Approximately. Anyone?

    Male Speaker 2: 90%.

    Steve McClain: 90? Okay. I’ll say a 100. That’s fine. Nearly all of it. The nail matrix in general is not involved but it may be. But the absence of involvement proximally is what gives us hope about treating things, that we can clear this. This is tinea pedis, common accompaniment. And when the skin comes off in sheaths like this, it’s pretty much diagnostic. And if you zoom in, you could actually see some large hyphae forms here, I think so. Just as you can see among the wall of the bottles in which we culture them. Onycholysis, very powerful, splitting of the nails. Within all these splits, there are fungi. There is one here, there is some here, there’s here, here. And it’s the fungal materials in there is splitting apart the nail. The split actually begins down below because these proliferate in the nail bed squamous part and then they’ll blossom. So a whole group of fungi will bloom at the same time and it’s PAS positive.


    You might see it a little bit here. This is where the Alcian blue really helps out or the combination of the PAS plus the Alcian blue. In this case there’s even some melanin pigment. What’s my gripe about the table here? Well first of, it’s ungual not subungual. The second is that it’s a nail bed infection. The lab, as I said, is a 50-50 proposition or used to be. And these were debris. How many times have you seen the word debris in a medical paper? What does debris mean? Would have been better off calling it cheese, okay? At least that would be more descriptive than just debris. Was this debris after a hurricane, debris on the side of the road? Debris. And my last complain is that they didn’t define what was normal. What is the normal thickness of the toenail, does anyone know? Well, I’ll tell you. So, updating this, we agree with the discoloration, tinea pedis is a very powerful independent criterion, onycholysis, powerful. What we disagree about is, what is the nature of this debris? So I’m going to give you my description here that it resembles cheese, it’s more like plastic biochemically, it’s a fungal polymer that cross links, it’s infectious, and it’s a mass, it doesn’t go away readily, okay? So, if you treat the nail bed and clear it but leave this fungal biomass, it can re-infect the nail bed. It is a nail bed infection, not a nail plate as was listed in this paper. And the normal toenails measure less than a millimeter, more like less than 0.8 millimeters. And what we can add to the lab is that by adding the Alcian blue to the PAS stain, more than 90% of the nails that you submit to me are now positive. So, instead of a 50-50, now it’s 9 to 1, or maybe 99 to 1. Cheese test positive or negative? I hear a positive. Okay. You say, well, that’s a goofy way to say it, Steve. And it is a little bit goofy but making an observation and scoring is an important part of tool that one can use. Here’s the nail plate and it’s discolored but notice most of the accumulation is here. Or look at this one, you got a little bit of nail plate. Look at all the nail bed up, cornified cells here. If we look at these in section, this is the nail plate up here, this is nail bed down here, but it’s all red. Okay. Eosin is a pretty decent stain of fungal products. Not necessarily of the hyphae themselves but of the fungal acid products that are in the nail. Okay. Here’s something that’s new and I bet you don’t know this, because I didn’t know this myself until a few years ago. But the squamous nail bed epithelium is infected and it needs treatment. In fact, that’s the site of action for Lamisil. It accumulates in these cells. You say, well, where is the hyphae? There aren’t any hyphae here. But you notice this nucleus here. The normal nucleus should look something like this. This nucleus is pushed off to the side by this red inclusion. And some of the inclusions actually have vacuoles in them. Here is another one here. Oops, sorry about that. Here’s one that almost looks like a protrusion into the nucleus. The nail bed squamous epithelium, all the way down at the base, needs treatment. So if you’re trying to get topicals down to there, you’ve got to get them into the nail bed epithelium, okay. Here’s another one that doesn’t exactly look the same except here is one of these where the nucleus is kind of cuffed around this inclusion. And you’ve got this kind of strange streak-like things. But notice all these blue staining. These are hematoxylin staining, intracellular forms, okay. Those aren’t normal. Okay. So the infected squamous epithelium needs treatment. We’re going to through a few cheese nails for a while and see if you agree or disagree. This is the undersurface of the nail and so note this little mound here. But the whole thing is fungal. It’s 100% fungal from top to bottom, from beginning to end. And where that heaped up area in the center, you can see it’s PAS and Alcian blue. In fact, there’s so much Alcian blue you can’t even hardly see the PAS. But there are some PAS positive forms. And note this kind of line here, very prominent in these nails.


    You flip it over and look on the other side and it kind of resembles a clam shell or an oyster shell or something, these parallel wavy lines, little onycholysis here, some splitting, pretty common appearance actually. Anyone, cheese or not cheese? This one we can’t see so well but there’s almost a leaf-like configuration. If you see something in a nail that looks like a plant, you’re probably right, dermatophyte. Cheese test positive. Somebody is almost, just more than cheese, you just say “yuck” when you see it. Oh, my god, what is that? Here is the low power, the eosin. I’ve been showing you too many hyphae but the eosin is when you see in one of my reports, the red from the eosin, that’s an abnormal nail that’s staining. It’s an accumulation of eosin staining components. Not necessarily the hyphae but a fungal product. This one is kind of fun. This is the undersurface of a nail and you notice there’s a little bit of orange here. But look on the other side, you got a split nail. When you see somebody that has what looks like the most god awful nail paint, in fact I call it that, the awful nail paint sign. If it looks like brown, they’re covering something up. The only reason for putting on that ugly of a nail polish is to cover up something that’s even uglier underneath. You’ll see that. When you go back in the clinic, you’ll think of me and you’ll say, oh, yeah, that nail polish is so ugly, there’s got to be fungus under there, and you’d be right. This does not project especially well but let’s go to the next one, maybe a little bit better. You see these thread-like, sometimes with treatment the nails initially look worse. As you clear up some of the easy fungus, now these thread-like, root-like structures that are coming out of this part become more apparent. And you have to warn your patients that their nails may actually look worse two weeks later but they will get better. So what is the thickness of the normal toenail? We’ll go through this. So, write down, you’ve got a piece of paper, well, write down your five nails, one, two, three, four, five. I don’t know if you can see that, I can’t see these so we can’t have you score them. But the podiatrist who did this scored this one as positive and all the others negative. This is kind of a misshapen nail. You can’t really see these in this projector, I’m sorry to say. But by the PAS scoring, positive, positive, positive, positive. In general, when you see one nail that’s positive, you can count on three or four or the other ones being positive as well. They’re just more subtly involved. Another way of looking at it, same nails. Now we measure the thickness so the thickness was 1.1, 0.8, 0.5, 1.0. These black ones are all positive as well. The only normal looking nail, the only normal nail by thickness, by PAS, and by clinical exam was this third one. Okay. So we made a men’s and women’s and it turns out men’s toenails are different than women’s toenails slightly by thickness. Men’s toenails, the hallux, one, two, three, four, five on the right, men’s are thicker than women’s. The purple is the overlap between men’s and women’s and the pink is the women’s side. And in women’s, the fifth toenail is often as thick or thicker than the first toenail, distinctive profile in women and men. So they differ by gender and by toe. So the thickest is one. In women, the fifth toe was as thick as the first toe. Okay. And the thickness is about half a millimeter, plus or minus 0.2 millimeters. We sampled 1200 toenails to get that data. It was rejected by the [indecipherable] [24:18] but maybe with your help we can recruit more patients. Some of the nails you look at, I mean it’s just the yuck test that doesn’t even look like cheese, it’s brown, you say yuck. And just immediate revulsion is a sign that there’s something growing in here. Inside that pigmented nail you’ll find these chitin structures, you notice a tube here and here. Fungal chitin, it polymerizes and cross links so much and it’s tough like an insect shell and in fact it refracts polarized light. It resembles glass. It’s so tough. Okay. Melanin, you can find in this.


    This is a little too zoomed in. But sometimes it’s obvious from the structure of the melanin that there’s fungus growing in there, dematiaceous fungus. So in our lab, the criteria is when we see a cheese test positive then we’re going to keep staining until we find at least three PAS positive or three Alcian blue positive hyphae. And so the combination of the blue and the red is useful. When you see them together and they have glommed on to each other, you can be pretty sure that that’s structure is fungal, even if you don’t necessarily recognize it as a hyphae because these fungi have a number of different forms that I did not know until a few years ago. Okay. This is a fetal toenail, week 17 and this is the third toe. And I want to use this to point out embryologically the nail matrix comes right down onto the distal phalanx. And this is an immature bone forming. This is the periosteum around here. But notice this collagenous structure that ties in to the sulcus and ties in to the proximal matrix. So, a thick nail has pretty close access, doesn’t take much trauma to get down here. And this at week 17 so it’s a pretty thin nail but the same principle holds true for adults, the same structures are there. Okay, how many cheese nail is here? Anyone? One, two, three, four, every single one of them. Tinea pedis, pretty common. But what happens when you start debriding this and it bleeds? We’ve found several cases like this where some of them go on to ulcerate when untreated and with treatment did not ulcerate. We don’t know whether they would have ulcerated or not but this to me is a sign of impending gangrene of the third toe. When you get down and it starts bleeding that needs to be treated. Okay, summary. The infection foments in the nail bed. All thin nails need to be treated. In fact, when I give out an antifungal, I told them to treat all 20 nails. Because usually, it’s pretty common to have one hand and two feet, right, your dominant foot from picking your toe fungus. It’s a serious infection in diabetes and I would urge you to think about, as you enter you practice lives, when you see diabetics with a toe fungus that you need to think about treating them. You need to do more than think about it. I think you do need to treat them. Onychomycosis is difficult to detect and so what happens is that in the old days, I had about 50% nail dystrophy and about 50% toe fungus. As my methods have improved, I now see nail dystrophy as a diagnostic myth. It’s a false negative lab test. If we do enough stains, if we do enough cultures, you’ll find the fungus. If anyone of you wants to participate in the normal nail study, we’re trying to finish it by the end of the year. Photograph, score them and [indecipherable] [28:31], submit them in 10 separate nail bags to my attention. In closing, toe fungus is not the most important part of my work, wound healing is. What led me to podiatric pathology was wound healing, my interest in wound healing. We’ve been studying wound healing at Stony Brook for a long time and you say, well, here is the day 28, this is an animal study, and here is a diabetic wound, it started out 6-millimeter punch biopsy that went right through the fat and it’s healed completely in 28 days. The glucose was 600 at this time. You say, well, that’s pretty good until you look at the normal. The normal measures about 0.9 millimeters, this measured 2.7 millimeters across. And notice the thickness of the scar. And notice this one is blue, bluer than this one. It’s about 50% more blue, in fact. There is about 50% more collagen. This is a trichrome stain and in a trichrome stain, collagen stains blue. These tend to have gapping wounds and when they heal, the amount of granulation tissue in here is usually thin. So these are thin gaping wounds. There’s not much tensile strength in these. Okay. The normals end up with a thicker, stronger scar, has more collagen in it.


    Okay. So, in closing, well, my main interest may be wound healing. The toe fungus, what is not known about toe fungus is surprising. Many of these, I think one of the mistakes the podiatrists make is in not biopsying enough. If you’re getting too many false negatives from your lab, there are some things you can do about. You can submit more nail samples. If it’s a 50-50 and you submit all 10 nails then one would guess in real toe fungus about four or five of them should be positive. So just submitting more sample would help. I look forward to talking to you in the future about working diabetic foot ulcers because I think that is where the podiatrists can have a real difference. Dermatologists are not doing much work in this field. Surgeons are not doing much work in this field. Where the podiatrists have an avenue or an opening is in scientifically tackling these foot ulcers and improving your care. When you have a niche that no one else can even come close to your treatment, the patients will flock to you. Thank you for your time.