Pattern recognition can save a life

Episode 5
11:08 minutes


A dermatologist is paged to examine a rare condition. But something doesn’t add up.


David Harker, M.D.
David Harker is in his final year of dermatology residency at the University of Texas Southwestern Medical Center in Dallas, Texas. This summer he will be joining a private practice in Hickory, North Carolina. You can follow David on twitter @HarkerDavid. 



Pattern recognition can save a life

[Intro music]

Raj: A 23-year-old man presents to urgent care with red and purple discoloration of the skin. He’s covered in papules, nodules, and plaques.


Raj: This is DDx, a podcast from Figure 1 about how doctors think.  This season is all about dermatology. I’m Dr. Raj Bhardwaj. Today’s case comes from Dr. David Harker. 

David Harker: I’m currently in my last year of dermatology residency at UTI Southwestern Medical Center in Dallas, Texas.


Raj: Dr. Harker was on call when he received a peculiar message.

David Harker: I was at home, taking home calls, had the pager on and I got a page. It was like a Thursday night, I think, at around 8:00 or 9:00. And the consult page comes through with like a little text on the pager that gives a one liner about what the question is about. Then a phone number to call back. So it said, you know, a young man presenting to the urgent care with a rash, concern for porphyria. That was like the question that the urgent care –  I think was a P.A. – who is consulting me had, which is interesting. That’s a pretty rare diagnosis. So, you know, I was interested immediately in what their consult question was.

Raj: Porphyria is an uncommon disorder that inhibits the body’s ability to produce heme, one of the essential components of hemoglobin. 

David Harker: So I called them back. They had put some pictures in the chart already, which is always helpful when you consult dermatology and is one of the nice features of the electronic medical records system today. So I had looked at the pictures while I was talking to the provider. And she’s told me, you know it’s this young guy, he’s coming in with fevers. He’s got this rash. Doesn’t really have any other medical history.

Raj: Dr. Harker was intrigued, and went into the clinic to examine the patient.

David Harker: I went to see him in the urgent care. The rooms, they’re unfortunately not very well lit when, you know, lighting is always important for dermatology. But you go in and he’s in this room with his mom. He was sitting on the bed, didn’t appear in any real acute distress, but obviously was nervous. And while I was examining him, I noticed multiple… the classic description for them was like kind of plump, plum-colored or they look like bruises. But these violaceous, nodules on his scalp, he had multiple on a scalp, one on his… A couple on his chest, his arms, his back. And mixed with those kind of in the background of multiple sort of red, brown or bruise-like patches, papules, and plaques over his chest and other places on his trunk. I also found a violaceous nodule on his gingiva in his mouth. 

Raj: It became clear that the patient’s presentation was not consistent with porphyria. 

Harker: So there’s categories of diseases in dermatology. We group things by kind of what the primary lesion is or what’s like what’s the essential process of this rash or lesion or whatever we’re looking at. So porphyria, we would group under what we call like a vesiculobullous disorder where it produces blisters and erosions in the skin. And he didn’t have any of those. He had nodules and plaques which would put him in a different diagnostic category entirely. Dermatologists really harp on how to describe a rash. And some people think in the age of an EMR, that’s not really important anymore. You can just put pictures of it in the chart. 

Raj: Medical trainees aren’t always taught how to describe a rash like a dermatologist would. For example, a papule is an elevated, solid, non-fluid-filled lesion less than one centimetre in diameter. A nodule is just a big papule. A plaque is a flat, either elevated or thickened lesion, greater than 1 centimetre across, which is often a coalescence of papules.

David Harker: And I hear all the time. Oh all rashes look the same like, you know, they’re all the same to me as just a rashy rash. But to me it’s when I hear that I think about Sherlock Holmes, like what he said to Watson where he said, you know, Watson, you see, but you don’t observe. And that’s how I feel like if you’re a lot of people approach dermatology that way, they just see the rash, but they don’t observe it. And really, you have to observe it and look at it carefully and see what the features are. What’s the primary lesion? What’s the distribution? What’s the color? Are there any secondary features like scale or excoriation, like the patients been scratching it? Are there multiple different morphologies because sometimes you can see a rash that looks like one thing, one place and looks differently on another part of the body.

Raj: That’s where pattern recognition comes in. It’s like seeing a familiar face in a crowd — You either recognize it or you don’t.

David Harker: If you correctly describe a rash, it means you correctly identified the salient features of it, which means you can then build the appropriate differential, because if you don’t describe it correctly or you think the primary lesion is something else, you could go chasing the completely wrong diagnosis, which essentially I think is what happened to this patient when he came in.

Raj: Dr. Harker still didn’t know exactly what the patient’s diagnosis was, but he was able to rule out porphyria almost immediately. In part, because of how dermatologists think.

David Harker: You know, I’m not really sure why they thought he had porphyria. So, you know, the way we think about things in dermatology is the physical exam is the primary way we make our diagnostic differential. And then history sort of supports that. It’s kind of backwards to most of medicine where you initially, you know, meet the patient and you ask a bunch of questions. You do the history and then you do the physical exam. And I was taught in medical school that you can usually make the diagnosis based solely on history with a patient probably 80 percent of the time. But that’s definitely not true in dermatology. Oftentimes the way I approach a patient is preferably they you know, when I meet them, I have them change into a gown and then I’m actually examining them while I’m talking to them, because really it’s what I’m looking at that’s most important.

Raj: And what he was looking at was alarming.

David Harker: I’m looking at the images and he has these violaceous, nodules and papules and plaques scattered over his chest and back and extremities. He had one on his forehead. I was really concerned for lymphoma or some kind of hematologic process. I talked to him and his mom, who is there with him at the urgent care. Did a biopsy at bedside right there to send off for path, and then recommended that he be admitted for expedited workup because this had been rapidly progressive just over. He said over like three weeks he’d started developing these skin lesions. Then they’d just been progressing and he’d been having fevers and night sweats and losing some weight. So all very concerning signs. 

Raj: Dr. Harker focused on the onset of the patient’s symptoms.

David Harker: He said he just initially he’s complained of like, he said he first felt some nasal congestion and then noticed… I think he said the first spot he noticed was on his chest. It may have been his arm, but just noticed these new bumps. They’re asymptomatic. They weren’t bothering him, but he just noticed more of them popping up over a few-week period. Then he started having regular fevers and like night sweats and weight loss, and that’s what finally prompted his mom to kind of like bring him into the urgent care. 

Raj: Even though the patient’s dermal symptoms weren’t terribly bothersome, the “red flag” systemic symptoms like fevers, weight loss, and night sweats were concerning.

David Harker: I was looking at his skin and then he’s telling me these have been rapidly progressive over a few weeks associated with fever, night sweats, weight loss like those are all just buzzwords for… like those are B symptoms. He’s having some kind of hematologic malignancy process potentially going on. 

Raj: But he still couldn’t pin down the exact diagnosis. So he called for some outside help.

David Harker: My attending physician who I was communicating with, when I went to see the patient, you know, when he reviewed the images in the chart, he actually sent me an article and said, like, you know, I agree with you. It’s probably in like the lymphoma-leukemia category. But here’s an article on this rare condition called blastic plasmacytoid dendritic cell neoplasm. It may be that. 

Raj: The characterization fit, as did the symptoms and presentation.

David Harker: And I was totally blown away when that’s what the biopsy results showed. And this is obviously not something I was expecting to diagnose on sight. And that wasn’t the diagnosis I was thinking of, I just had a category in mind because of the way he was presenting. 

Raj: Blastic plasmacytoid dendritic cell neoplasm – or BPDCN – is a rare, aggressive cancer, which often presents with features of both lymphoma and leukemia, with skin involvement in about 80% of cases.

David Harker: It’s very uncommon and unfortunately has a rather poor prognosis, so I think it was good we caught it early. You could think of it like a leukemia or a lymphoma. Has a high instance of showing up in the skin, like it really likes to manifest in the skin. And there is … since it’s so rare, there’s not a lot of well-designed like large studies regarding treatment.


Raj: Even though the physician’s assistant thought this was something else entirely, they were right to call the dermatologist. A simple approach is to look at the rash, AND at the patient: is this a rash in a person who looks well… or who looks sick? This patient, with his fevers, night sweats, and weight loss over three weeks, was definitely sick.

David Harker: It’s not an uncommon occurrence on the consult service for sure to be called and the team says, you know, we think the patient may have this thing and then they end up not having that. That happens fairly commonly. And I think, again, that’s just a reflection that people just don’t get a lot of — medical providers, doctors, PAs, NPs – they just don’t get a lot of dermatology education if they’re not dermatologists.

Raj: Dermatologists use particular words to describe rashes, and they can get frustrated with less precise language. Using common terms helps both health care providers and our patients.

David Harker: It’s important to try to learn it because dermatologic disease is a source of a lot of morbidity for patients. I think it’s easy to dismiss rashes as, oh, it’s just like a rashy rash it’ll probably go away with topical steroids. What’s the big deal? And even though the vast majority of dermatologic conditions are not life threatening, it doesn’t mean they don’t cause suffering for patients. And I think there’s just a lot of underappreciated under-recognised suffering associated with dermatologic disease.


Thanks to Dr. David Harker for speaking with us. 

This is DDx, a podcast by Figure 1.

Figure 1 is an app that lets doctors share clinical images and knowledge about difficult-to-diagnose cases. 

I’m Doctor Raj Bhardwaj, host and story editor of DDx. You can follow me on Twitter at RajBhardwajMD

Ddx is produced by David Crosbie for Earshot Podcasts.

Sound design and mixing by Chandra Bulucon. 

Our theme music is by Nathan Burley.

The executive producers of DDx are Jesse Brown and Kevin Sexton.

Head to, where you can find full show notes, photos, and speaker bios.

Thanks for listening.