Often my coworkers will have me perform a “drive-by consult” on their patients to determine if a plantar lesion is a wart or a callus. We have all learned the traditional squeeze maneuver to determine if pain is present on direct pressure (callus) or pain when laterally squeezing the lesion (wart).1 We have all looked for the visual signs: lack of dermatoglyphics running through the lesion, presence of black dots (thrombosed capillaries), scalloped border, pinpoint bleeding upon debridement, the anatomic location of a traditional callus, etc.
We also know that sometimes visual clues and physical signs fail us when examining these lesions. This might be due to various remedies that the patient or previous clinicians have applied to the wart/callus, the age of the lesion, and/or anatomic location. So what can we use in these instances to determine what we are dealing with? What about determining if a wart is responding to therapy (i.e. resolving)? I use dermoscopy in these cases.
You might question the use of dermoscopy. Why should you purchase a dermatoscope when you can’t bill for using it? I use it on the majority of my patients—from warts to nails to what it was originally intended for (pigmented lesions). It has been a practice builder for me, not a detriment. Once you know what you are looking for, it takes seconds—not minutes—to get a visual diagnosis. Using the dermatoscope in this one aspect—determining wart presence and/or resolution—has made a huge difference for me.
Haven’t you had the warty lesion that really looks like it’s dead and gone? Then you discharge the patient and he or she returns in a few weeks with a warty resurgence? Yes, that happened to me in my practice. Then I bought a dermatoscope, learned how to use it, saw the visual changes the wart went through on its way to the verruca graveyard and learned when it was time to truly discharge a patient from care.
What does a “normal” plantar wart look like under the dermatoscope?2 Post-debridement, you most likely will see pinpoint bleeding or black dots. Obviously, as treatment progresses, you will see this slowly decrease, ultimately leading to complete clearance both visually and with a dermatoscope. In a plantar wart that has staked its claim on the foot, I also see lobules/honeycomb-like structures populating the lesion that may or may not have the tiny vessels incorporated in it. These also decrease as the dermatoglyphics return. However, sometimes as I see the dermatoglyphics return, there is a “papilliform” type appearance, which I interpret as “bumpiness” or a wavy shift of those skin lines. This represents non-resolution of the verruca even though it may appear visually cured to the naked eye. That is what has made a difference so many times in my practice. What looks resolved to the naked eye genuinely really isn’t resolved and may require one or two more treatments to see total clearance via the dermatoscope.
What does a callus look like under the dermatoscope? It has a translucent central core that may or may not have skin lines present. It lacks the distinguishing characteristics of a verruca of course.
1. Zaiac M, Mlacker S, Shah VV, Simmons BJ. Clinical pearl: the squeeze maneuver. Cutis. 2016;97(3):202, 204
2. Bae JM, Kang H, Kim HO, Park YM. Differential diagnosis of plantar wart from corn, callus and healed wart from with the aid of dermoscopy. Br J Dermatol. 2009; 160(1):220–22.