Ep 127: A 65-Year-Old Male with a Spot on His Foot

This episode presents a 65-year-old man with a new pigmented lesion on the sole of his foot. The discussion focuses on the differential diagnosis.

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Transcript

[upbeat intro music] 

[Dr. Handy] Hi everyone. Welcome 

back to Harrison's Podclass. 

We're your co-hosts. I'm Dr. Cathy Handy. 

[Dr. Wiener] And I'm Dr. 

Charlie Wiener and we're joining 

you from the Johns Hopkins 

School of Medicine. 

[music continues] 

[Dr. Handy] Welcome to episode 127: 

a 65-year-old man with a spot on his foot. 

[Dr. Wiener] Cathy, today's 

patient is a 65-year-old 

African-American man who comes 

to the clinic complaining 

or telling us about a spot on his foot. 

He noticed it a few months ago and he says 

it's been getting bigger 

over the past two months. 

It's on the bottom of his foot, 

so he is not exactly sure 

when it first appeared. 

He denies any local or systemic symptoms 

associated with this. 

His only medications are 

metformin for diabetes 

and losartan for hypertension. 

On physical examination, 

his vital signs are all 

within normal limits. 

You take a closer look at his foot 

and you see that there's about 

a half a centimeter round, 

dark, macular lesion 

with irregular borders. 

It's not tender on exam 

and you cannot feel it when 

you're rubbing over it. 

So the question's going to ask, 

which of the following is 

the most likely diagnosis? 

And the options are A. 

acral lentiginous melanoma; 

B. diabetic foot ulcer; 

C. dysplastic nevus; 

D. lentigo maligna melanoma; 

or E. syphilis. 

[Dr. Handy] Well, I'd 

love to see a picture, 

but since this is a podcast, 

we obviously can't do that. 

[Dr. Wiener] Well, the picture 

can be found in the 20th 

edition of the Harrison's 

Self-Assessment book, 

but I think there are 

aspects of the history 

and the description that help 

you get to the right answer. 

[Dr. Handy] Absolutely. So 

first, I am struck by the fact 

that it's non-tender, 

non-raised, and not red, 

so that makes infection less likely. 

I recognize that he has diabetes 

and those patients are 

prone to foot ulcers 

and infections that may not be painful, 

but the bottom of the 

foot would be unusual. 

And given what sounds like mild diabetes 

and a normal sensory exam, 

it doesn't sound like he 

has extensive neuropathy. 

So I'm going to rule out the 

diabetic foot ulcer as a cause. 

[Dr. Wiener] Okay. What's next? 

[Dr. Handy] Well, the next 

notable thing is the timing. 

So he reports that the lesion 

has grown in two months. 

Dysplastic nevi are benign, 

irregularly pigmented 

and shaped melanocytic hematomas 

with some atypical cellular features 

and are frequently associated 

with familial melanoma. 

These would not be expected 

to increase in size over 

a short period of time, 

so we can rule that out too. 

[Dr. Wiener] Okay, so it's not B or C. 

What else can you rule out? 

[Dr. Handy] We can also 

rule out, E. syphilis. 

So remember, primary syphilis presents 

with a chancre on the genitals, 

so this would have to 

be secondary syphilis. 

The lesions of secondary syphilis 

are initially pale red or pink 

non-pruritic discrete macules 

distributed on the trunk and extremities. 

These macules progress to papular lesions 

that are distributed widely 

and that frequently involves 

the palms and soles. 

A syphilitic lesion would not be expected 

to be a solitary isolated 

lesion on the sole of the foot. 

[Dr. Wiener] Okay, well, 

that leaves us with 

acral lentiginous melanoma 

and lentigo maligna melanoma. 

Two types of melanoma. 

Let's talk a little more 

about melanomas broadly first 

and then let's narrow it down. 

[Dr. Handy] Yeah, given the gravity, 

we must consider melanoma 

in the differential 

of any new skin lesion, 

particularly, a pigmented lesion. 

Melanoma is an aggressive 

malignancy of melanocytes, 

pigment-producing cells that originate 

from the neural crest 

and migrate to the skin, 

meninges, mucous membranes, 

the upper esophagus, and eyes. 

Melanocytes in each of these locations 

have the potential for 

malignant transformation, 

but the vast majority of 

melanomas arise in the skin, 

often permitting detection at a time 

when complete surgical 

excision leads to cure. 

Cutaneous melanoma can occur in people 

of all ages and all colors. 

Clinical features that 

confer an increased risk 

for melanoma include 

vulnerability to sun damage, 

so that's with light coloration 

of the skin, hair, or eyes; 

photodamaged skin or history of exposure 

to lots of UV rays; 

abnormal growth of melanocytes 

and immunosuppression. 

[Dr. Wiener] Tell me 

about the different types 

of melanoma, two are mentioned here. 

As you mentioned, sun exposure 

is a major risk factor, 

but this lesion is on 

the bottom of his foot, 

not a common place, or people 

don't let the sun shine 

on the bottom of their feet that often. 

[Dr. Handy] Yeah, lentigo 

maligna melanoma occurs 

on sun-exposed skin as a large, 

hyperpigmented macule or plaque 

with irregular borders 

and variable pigmentation. 

As the bottom of the foot 

is not a skin-exposed area, 

this is less likely in this case. 

Now, acral lentiginous melanoma 

is the most common melanoma in Blacks, 

Asians, and Hispanics and occurs 

as an enlarging hyperpigmented macule 

or plaque on the palms and soles. 

In non-white populations, 

the frequency of acral and 

mucosal melanomas is much higher; 

the incidence of melanoma in Black 

and Hispanic populations is not associated 

with UV light exposure. 

[Dr. Wiener] Okay, so the 

answer to this question is 

A. acral lentiginous melanoma. 

What would be the next step? 

[Dr. Handy] Any pigmented cutaneous lesion 

that has changed in size or shape 

or has other features suggestive 

of malignant melanoma is 

a candidate for biopsy. 

An excisional biopsy with 1-3 

millimeter margins is suggested. 

This facilitates histologic 

assessment of the lesions 

and you can also get a measurement 

of thickness if the lesion is melanoma, 

and it constitutes definitive treatment 

if the lesion is benign. 

For lesions that are 

larger on anatomic sites 

where excisional biopsy 

may not be feasible, 

an incisional biopsy or partial biopsy 

through the most nodular 

or the darkest area 

of the lesion is acceptable. 

This doesn't appear to facilitate 

the spread of melanoma. 

For suspicious lesions, 

though, every attempt 

should be made to get the deep 

and peripheral margins to 

perform immunohistochemistry, 

since that's important to 

the staging of melanoma 

and deciding on the next 

steps if it is melanoma. 

[Dr. Wiener] So for this man, 

the next step would be a biopsy. 

[Dr. Handy] That's right. 

[Dr. Wiener] Okay, so the 

teaching points in this case 

are that any changing skin lesions 

should be considered melanoma 

until proven otherwise. 

Generally speaking, there 

are two forms of melanoma. 

Lentigo malignant 

melanoma typically occurs 

in sun-exposed areas, whereas 

acral lentiginous melanoma, 

which is more common in 

Blacks, Asians, and Hispanics, 

may occur on the palms and the soles. 

[Dr. Handy] You can 

find questions like this 

and this question in the 

Harrison's Review Questions, 

and learn more about this in 

the chapter on skin cancer. 

Visit the show notes for 

links to helpful resources, 

including related chapters 

and review questions from Harrison's. 

And thank you so much for listening. 

If you enjoyed this episode, 

please leave us a review 

so we can reach more 

listeners just like you. 

[upbeat outro music]