Naevi

Question 1

What does the MC1R gene do ?

Answer 1

Codes for the melanocortin 1 receptor (MC1R)

Question 2

Where is the MC1R protein located and what does it do ?

Answer 2

Located on the plasma membrane on melanocytes

It converts phaeomelanin (red hair) into eumelanin (hair colour other than red)

Question 3

What happens if there is one defective copy of MC1R gene and what also happens if there is two defective copies ?

Answer 3

• One defective copy results in freckles
• Two defective copies results in red hair

Question 4

What are the clinical features of freckles and who are they most common in ?

Answer 4

• They are patchy (macules) increases in melanin pigmentation, occurring after UV exposure. They become more prominent in summer and fade in winter
• They esp arise on the mid-face but can be more widely distributed
• Usually small in diameter < 3mm
• Most common in fair skinned and red heads

Question 5

What is shown in this pic ?

Answer 5

Freckles (ephelides)

Question 6

What are freckles & lentigines caused by ?

Answer 6

• Freckles are caused by increased melanin production of melanocytes (no increase in melanocytes is seen)
• Lentigines are caused by localised proliferation of melanocytes (increased melanin and basal melanocytes)

Question 7

Do freckles require any treatment ?

Answer 7

No - just advice sun protection

Question 8

What are actinic lentigines and where on the body do they mainly occur ?

Answer 8

• They are very similar to freckles but are larger, more defined than freckles & they do not fade during winter (persist in the absence of UV radiation)
• Most often found on the hands and face as related to UV damage

Question 9

What are the clinical features of actinic (solar) lentigines

Answer 9

• Larger & more defined than freckles
• Colour usually uniform with yellowish or greyish light-brown hue.
• An irregular border may give it a scalloped shape.

Question 10

What is an atypical actinic (solar) lentingo?

Answer 10

• It is an actinic (solar) lentigo with unusual characteristics.
• Making it difficult to determine if it is a benign actinic (solar) lentigo or melanoma in situ

Question 11

What are the clinical features of an atypical actinic lentingo ?

Answer 11

It is a solitary and distinct macule. When compared to surrounding solar lentigines, an atypical solar lentigo may:

• Be larger in size and more irregular in shape
• Have a sharper or less distinct margin
• Be darker in colour and have a greater variation in colours
• Be inflamed (red) or there may be areas of hypopigmentation (loss of colour)
• Have greyish or purple discolouration due to an inflammatory reaction.

Question 12

How are freckles & lentingos diagnosed ?

Answer 12

• Clinically, unless uncertain e.g. it is an atypical actinic lentingo then do dermatoscopy
• Atypical actinic lentingos are usually then excised

Question 13

What is a melanocytic naevus ?

Answer 13

It is a benign melanocytic neoplasm (abnormal growth) - more generally known as naevus or mole.

Question 14

What are the 2 main ways in which melanocytic naevus may be termed ?

Answer 14

Congenital (from birth) or acquired (most common) - usually during the first 2 decades of life

Question 15

Note - congenital melanocytic naevi covered in paediatric dermatology

Question 16

Describe the common features of a common acquired naevus

Answer 16

• Very common in white individuals
• Small, symmetrical, well-circumsised hyperpigmented macule or papule (flat or protruding)
• They may arise on any part of the body.
• They vary in colour from pink or flesh tones to dark brown, steel blue, or black.
• Although mostly round or oval in shape, moles are sometimes unusual shapes.
• They range in size from a couple of millimetres to several centimetres in diameter.

Question 17

Describe the development of acquired naevi

Answer 17

Question 18

What are the two types of dysplastic (atypical) naevi?

Answer 18

Sporadic and familial

Question 19

Describe the typical features of an atypical naevi

Answer 19

Mole with at least 3 of the following features.

• Size >5 mm diameter
• Ill-defined or blurred borders
• Irregular margin resulting in an unusual shape
• Varying shades of colour (mostly pink, tan, brown, black)
• Flat and bumpy components

Question 20

Describe the features of sporadic naevi

Answer 20

• Not inherited
• Usually 1-10 atypical naevi
• Risk of MM slightly raised

Question 21

Describe the features of familial naevi

Answer 21

• Strong FH of melanoma
• Autosomal inheritance
• High penetrance eg CDKN2A
• Atypical naevi+++
• Lifetime risk melanoma up to 100%
• May be part of Familial Atypical Mole and Melanoma (FAMM) syndrome

Question 22

Are many atypical naevi dysplastic ?

Answer 22

No - Clinically atypical naevi are sometimes called dysplastic naevi, but this is term is best used for a specific microscopic appearance. Only a minority of clinically atypical naevi fulfill microscopic criteria for dysplastic naevus.

Question 23

What is the pathological criteria for a dysplastic naevi ?

Answer 23

• Architectural atypia AND cellular atypia
• There may be fibrosis or scarring in the dermis.
• Inflammatory cells may infiltrate the lesion.
• Unlike melanoma epidermis not effaced
• Severe dysplasia may be difficult to distinguish form melanoma in-situ
• Associated blood vessels may be increased in number or enlarged.

Question 24

What is the pic showing ?

Answer 24

Congenital melanocytic naevi

Question 25

Give some examples of rarer naevi

Answer 25

* Blue naevi * Halo naevi * Spitz naevi

Question 26

Describe the appearance of halo naevi

Answer 26

* It is an otherwise normal mole. * Have a peripheral halo of depigmentation (white). * They show inflammatory regression and are overrun by lymphocytes

Question 27

Describe the appearance of blue naevi

Answer 27

* **A solitary, bluish, smooth surfaced macule, papule or plaque.** * **They are generally round or oval in shape.** * Blue naevi-these are entirely dermal and consist of pigment rich dendritic spindle cells. The cellular variant may have mitoses and mimic melanoma

Question 28

Describe the appearance of spitz naevus

Answer 28

* Usually occur \<20 years * Most often presents as a symmetrical reddish or skin-coloured nodule * Most often affects the face and extremities