Naevi Flashcards
What does the MC1R gene do ?
Codes for the melanocortin 1 receptor (MC1R)
Where is the MC1R protein located and what does it do ?
Located on the plasma membrane on melanocytes
It converts phaeomelanin (red hair) into eumelanin (hair colour other than red)
What happens if there is one defective copy of MC1R gene and what also happens if there is two defective copies ?
- One defective copy results in freckles
- Two defective copies results in red hair
What are the clinical features of freckles and who are they most common in ?
- 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
What is shown in this pic ?
Freckles (ephelides)
What are freckles & lentigines caused by ?
- 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)
Do freckles require any treatment ?
No - just advice sun protection
What are actinic lentigines and where on the body do they mainly occur ?
- 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
What are the clinical features of actinic (solar) lentigines
- Larger & more defined than freckles
- Colour usually uniform with yellowish or greyish light-brown hue.
- An irregular border may give it a scalloped shape.
What is an atypical actinic (solar) lentingo?
- 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
What are the clinical features of an atypical actinic lentingo ?
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.
How are freckles & lentingos diagnosed ?
- Clinically, unless uncertain e.g. it is an atypical actinic lentingo then do dermatoscopy
- Atypical actinic lentingos are usually then excised
What is a melanocytic naevus ?
It is a benign melanocytic neoplasm (abnormal growth) - more generally known as naevus or mole.
What are the 2 main ways in which melanocytic naevus may be termed ?
Congenital (from birth) or acquired (most common) - usually during the first 2 decades of life
Note - congenital melanocytic naevi covered in paediatric dermatology
Describe the common features of a common acquired naevus
- 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.
Describe the development of acquired naevi
What are the two types of dysplastic (atypical) naevi?
Sporadic and familial
Describe the typical features of an atypical naevi
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
Describe the features of sporadic naevi
- Not inherited
- Usually 1-10 atypical naevi
- Risk of MM slightly raised
Describe the features of familial naevi
- 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
Are many atypical naevi dysplastic ?
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.
What is the pathological criteria for a dysplastic naevi ?
- 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.
What is the pic showing ?
Congenital melanocytic naevi
Give some examples of rarer naevi
- Blue naevi
- Halo naevi
- Spitz naevi
Describe the appearance of halo naevi
- It is an otherwise normal mole.
- Have a peripheral halo of depigmentation (white).
- They show inflammatory regression and are overrun by lymphocytes
Describe the appearance of blue naevi
- 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
Describe the appearance of spitz naevus
- Usually occur <20 years
- Most often presents as a symmetrical reddish or skin-coloured nodule
- Most often affects the face and extremities
