Lentigo Maligna

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Introduction:

Lentigo maligna is a subtype of melanomaThis glossary term has not yet been described. that arises on sun-damaged skinThis glossary term has not yet been described.. The term lentigo maligna denotes melanoma in situThis glossary term has not yet been described., whereas lentigo maligna melanoma (LMM) denotes invasive melanoma. We use LMM as a term that encompasses all melanomas (in situ and invasive) on sun-damaged skin. MelanomaThis glossary term has not yet been described. on sun damaged skinThis glossary term has not yet been described. (extrafacial) is covered in a separeate chapter LMMs occur most frequently in the elderly population. The common anatomic sites include the sun-damaged skin of the bald scalp and faceThis glossary term has not yet been described..


Clinical examination

LMMs are patches to flat plaques, variegate in colors that range from light brown to black, and asymmetric in shape. These lesions tend to enlarge slowly and if left untreated, cover an area of several centimetres while remaining flat, at times appearing discontinuous and patchy on clinical examination. To appreciate the extent of the clinical lesion, Wood’s lamp is an essential part of the examination, and often, it reveals that the lesion is much more extensive than it appears on naked-eye examination. With time, LMM may develop invasive foci clinically evident as papules, nodules, or thicker plaques. LMM at that stage confers risk of metastatic disease.


HistopathologyThis glossary term has not yet been described.

Histopathologically, findings in LMM include an asymmetric lesion with an abnormal proliferation of single melanocytes in the basal layer of the epidermis, the melanocytes being unevenly spaced and increased in density (crowded), and often extend down follicles. Even few nests of melanocytes in a broad, junctional lesion on the face that displays solar elastosis in the dermis (evidence of sun damageThis glossary term has not yet been described.) strongly raise the suspicion of LMM. An irregular scatter of melanocytes in pagetoid fashion (at suprabasal layers of the epidermis) also supports the diagnosisThis glossary term has not yet been described. of LMM. Nests and fascicles of melanocytes in the dermis attest that the melanoma is no longer in situ. LMM in the dermis may display at times desmoplastic and neurotropic features. Early LMM may be clinically subtle and difficultThis glossary term has not yet been described. to diagnose on the sundamaged background that displays many solar lentiginesThis glossary term has not yet been described.. Other differential diagnoses include pigmented actinic keratosisActinic keratosis (also called solar keratosis and senile keratosis; abbreviated as AK) is a pre-cancerous patch of thick, scaly, or crusty skin. These growths are more common in fair-skinned people and those who are frequently in the sun. They usually form when skin gets damaged by ultraviolet (UV) radiation from the sun or indoor tanning beds. AKs are considered potentially pre-cancerous; left untreated, they may turn into a type of cancer called squamous cell carcinoma. Untreated lesions have up to a 20% risk of progression to squamous cell carcinoma, so treatment by a dermatologist is recommended., lichen plaunus-like keratosis, and early, flat seborrheic keratosisThis glossary term has not yet been described. or solar lentigoThis glossary term has not yet been described.. On the face, a pigment network is usually absent due to the flattening of the dermoepidermal junction (DEJ) and effacement of the rete ridges. Thus, additional dermoscopic criteriaThis glossary term has not yet been described. are applied to diagnose early LMM.


Classic dermoscopy criteria (Stolz CriteriaThis glossary term has not yet been described.) [1]:


Hyperpigmented follicular openings

There is crescent-shaped pigmentation that accentuates in only one portion of the follicular opening. On histopathologyThis glossary term has not yet been described., this finding correlates with atypical melanocytes as single units or small nests extending down hair follicles. Correlation of dermoscopically identified asymmetric follicular openings using refl ectance confocal microscopyThis glossary term has not yet been described. (RCM) demonstrates a nonuniform infiltration of atypical melanocytes along the circumference of the follicular epithelium, explaining the asymmetric, crescent-shaped pigmentation seen en face by dermoscopy. On occasion one can see asymmetrically pigmented follicular openings in a solar lentigo; however, in a solar lentigo the colorColor (American English) or colour (Commonwealth English) is the characteristic of human visual perception described through color categories, with names such as red, yellow, purple, or blue. of the crescent-shaped area tends to be the same color as the surrounding area. In LMM the follicular openings can be symmetric or asymmetric but the color tends to be darker, often with a grayish hue. The following 5 pattern of hyperpigmented follicular opening can be observed:


Lentigo maligna schematic 1.jpg
  • Fine circle
  • Semicircle
  • Signet ring-like circle
  • Irregular circle
  • Double circle

Annular-granular pattern

Annular–granular pattern can be divided into dots aggregated around adnexal openings and short and polygonal lines around and between adnexal openings. These two components of the annular–granular pattern can be seen singly or in combination.


Lentigo maligna schematic 2.jpg

Dots aggregated around adnexal openings:

The findings range from brown dots to blue-gray granularityThis glossary term has not yet been described. scattered throughout the lesion, but often appearing to cluster around the adnexal openings (Fig. 8d.6). Based on dermoscopy to RCM and histopathology correlation, these findings are explained by aggregates of melanocytes and small nests at the DEJ between the follicles (brown dotsThis glossary term has not yet been described.) and by melanophages in the dermis (blue-gray granularity).

Short and polygonal lines around and between adnexal openings.

As the density of the brown dots increases, they coalesce to form short pigmented lines around the adnexal openings as well as between the adnexal openings. These lines are often polygonal, forming a zig-zag pattern. DermoscopyDermoscopy is a non invasive diagnostic method. to RCM and histopathology correlation suggest that these structures are due to confluent junctional nests and aggregates of melanocytes by the annular–granular pattern, the concentric dermoscopic appearance has been termed isobar (also known as circle within a circle).


Lentigo maligna schematics 3.jpg

Pigmented rhomboidal structures

Rhomboidal structures Elongation, thickening, and merging of the short polygonal lines around adnexal openings form a polyhedral-shaped structures that have been termed “rhomboidal” (in reality, the shapes vary but are all polygonal). The histopathologic correlation is similar to that of short and polygonal linesstreaks, albeit reflecting more extensive infiltration of the DEJ by confluent nests and aggregates of melanocytes.


Lentigo maligna schematics 4.jpg

Dark blotches and obliterated hair follicles

Dark blotches (also termed “homogenous structures”) with or without obliteration of the adnexal openings. Dark brown to black blotches are seen, initially with “sparing” of adnexal openings, appearing as light-colored holes within the blotchDark structureless areas , and eventually, as a homogenous black blotch with obliteration of the adnexal openings. It should be highlighted that the aforementioned melanoma-specific structures can be seen in lentigo maligna melanomas on the face and also in lentigo maligna melanomas arising on nonfacial chronic sun-damaged skin.

New dermoscopy criteria (Thomas criteria) [2]:

Darkening at dermoscopic examination

This defines the observation on dermoscopic images of the presence of a colour, invisible to the naked eye, and darker than all clinically observable shades of brown or grey. Target-like pattern We defined as ‘target-like pattern’ the presence of a dark dotSee [[Glossary:Dots|Dots]] in the centre of the dark circle of a hyperpigmented hair follicle. This dark dot was not a hair.

Red rhomboidal structure

We defined as red rhomboidal structure a lozenge-shaped vascular pattern occurring in the area separating the hair follicles from the others.

Increased density of the vascular network

‘Increased density of the vascular network’ was defined as a vascular network of higher density within the lesion than in peripheral skin.

ManagementThis glossary term has not yet been described. of pigmented lesions of the face

The first issue that needs to be addressed when evaluating a pigmented lesion on the face with dermoscopy is whether the lesion possesses any melanoma-specific structures. Although superficialThis glossary term has not yet been described. spreadingThis glossary term has not yet been described. melanoma is rare on the face, they can occur and thus all facial lesions need to be scrutinized for the presence of any melanoma-specific structures. If the lesion has any of the aforementioned structures then the lesion needs to be biopsied. If it does not have any of the above-mentioned melanoma-specific structures then the lesion is evaluated for the presence of features diagnostic of basal cell carcinomais the most common skin cancer, and one of the most common cancers in the United States.[1] While BCC has a very low metastatic risk, this tumor can cause significant disfigurement by invading surrounding tissues, solar lentigo, or seborrheic keratosis. If the lesion has no features to assist in diagnosis then the lesion should either be biopsied or subjected to digital monitoring for at least 6 months to one year.

Based on: Atlas of Dermoscopy by Marghoob A., Malvehy J., Braun




References
  1. Schiffner et al.: Improvement of early recognition of lentigo maligna using dermatoscopy. J. Am. Acad. Dermatol. 2000;42:25-32. PMID: 10607316.
  2. Pralong et al.: Dermoscopy of lentigo maligna melanoma: report of 125 cases. Br. J. Dermatol. 2012;167:280-7. PMID: 22404578. DOI.