Congenital Melanocytic Nevi

00:01 Welcome. Let's talk here about congenital melanocytic nevi or CMM.

00:07 And this is to be distinguished from acquired melanocytic nevi which will be the topic of a different talk. So cmms are just the common household mole.

00:18 They are pigmented skin lesions that are present at birth, hence congenital. And they're composed of a focal collection of proliferated melanocytes.

00:31 So the epidemiology of these they're actually quite common.

00:33 1 to 3% of newborns will have one maybe more.

00:38 Giant melanocytic nevi or congenital melanocytic nevi occur in about one inch 20,000. So the very big variety that we'll see at the end of the talk.

00:50 Kind of uncommon. But the regular household variant mole pretty common.

00:56 The pathophysiology of these.

00:58 So there is a genetic predisposition.

01:00 You can have somatic mutations in Braf which is a transcription factor.

01:06 It is a valine to glutamic acid mutation.

01:10 That's the V to E mutation in the 600th amino acid.

01:16 It's actually reasonably common in these.

01:19 You can also have in the large variety mutations in Nras, which is going to be a family that drives a family of genes that drive proliferation.

01:31 Notably, both Braf and Nras mutations are also going to be associated with melanoma.

01:38 I will say this now, but you should also keep in mind that these congenital versions almost never convert to into malignancy.

01:48 That is to say that driver mutations like Braf and Nras don't necessarily equate to malignancy. There are other changes that have to occur.

01:58 So what is this? What is this lesion.

02:01 It's just a proliferation of melanocytes and also migration of these proliferated melanocytes in deep to the basal layer and into the dermis.

02:13 The melanocytes of a congenital melanocytic nevus may migrate completely into the dermis, resulting in an intra dermal nevus as seen here on the right side.

02:26 The melanocytes start at the dermoepidermal junction and then gradually descend to become a junctional or compound nevus, present at both dermoepidermal junction and in the dermis, and then an intra dermal nevus as they mature.

02:42 Nivea have varying degrees of pigmentation and may be non-pigmented as seen here.

02:47 So for a clinical presentation, what do these look like? You as good doctors should be able to recognize them.

02:55 Most are small to medium sized and they tend to be solitary.

02:59 So when I say small 2 to 3mm up to maybe 1 to 2cm in size, depending on how much melanin is being produced by the cells, the color can range from tan to dark black.

03:12 They tend to have irregular borders, and because these occur in areas where hair would normally be Normally be produced, they may have hair within them.

03:21 So you have hairy nevi.

03:25 The large variant are often accompanied by multiple, smaller, widely disseminated kind of satellite nevi, and this is to be distinguished from similar acquired lesions.

03:35 So this is not the same as a Becker's nevus or Becker's melanocytic nevus.

03:41 And if you've never seen one, you can Google Richard Gere and look at his left shoulder. And there is a classic example of a Becker's that's to be distinguished, however, from these giant congenital melanocytic nevi, which are quite big with kind of satellite lesions.

03:58 How do we diagnose this? Well, it's kind of by inspection.

04:01 Um, you can also use a dermatoscope that will illuminate and give you a better sense of the kind of depth of invasion, etc., of, of the lesion.

04:12 And it can be very helpful in differentiating very small congenital melanocytic nevi from atypical acquired nevi.

04:20 I would leave the dermoscopic kind of evaluation to the cognoscenti, to people like dermatologists.

04:27 But you will undoubtedly use a dermatoscope in your clinical training.

04:30 And if you go into dermatology, you'll use it as part of your regular armamentarium. Uh, again, just to reiterate, the bulk of congenital melanocytic nevi are entirely benign.

04:45 They start benign and they end life benign.

04:48 The risk of melanoma arising in them is extremely low, despite the fact that many may be driven by proliferating specific mutations that cause increased proliferation.

05:01 How do we manage these? So it's mostly clinical observation.

05:05 Again very rarely they go malignant but the vast majority do not.

05:09 Um you may because of cosmetic reasons want to surgically excise them.

05:15 And they're certainly amenable to that.

05:17 You can also blast them with laser therapy.

05:20 So benign congenital melanocytic nevi are pretty common and pretty benign.