Palms and Soles
In multiple studies, dermoscopy has led to a significant improvement in diagnostic accuracy of skin tumors in acral sites. It can be also utilized to examine other skin disease in this location such as pyogenic granuloma, viral warts or tinea nigra or infestations such as tungiasis. In this chapter we will describe the dermoscopic aspects in acral skin both volar and non-volar sites. Ungueal dermoscopy will be described in a separate chapter of dermoscopedia.
Dermoscopy of acral tumours
Dermoscopic specific features of skin tumours in volar skin are driven by particular anatomic characteristics of the skin in this situation. In the case of non-volar skin similar dermoscopic patterns are seen in other skin sites such as extremities. Because of this we will describe in this chapter the Dermoscopy of pigmented and non-pigmented tumours of volar skin in palms and soles.
Pigmented lesions of volar skin
Diverse dermoscopic patterns in the palmar and plantar regions have recently been defined to distinguish between benign neoplasms and melanoma. The dermoscopic patterns reported in melanocytic nevi of these regions are the parallel furrow pattern, lattice-like pattern and fibrillar or filamentous pattern. In addition to these some nevi may exhibit patterns previously described in non-volar skin such as globular pattern, homogenous pattern and reticular pattern. In areas with the transition of volar to non-volar skin in the Wallace line the lesions may exhibit a combination of one the typical volar patterns and non-volar pattern. One additional pattern with the name of globule-strike pattern has been described in small lesions in dark skin type population. In contrast to acral nevi melanoma exhibits different dermoscopic features because of the invasion of the skin structures in this location.
The main specific dermoscopic patterns of acral lentiginous melanoma are the parallel-ridge pattern and diffuse multicomponent pigmentation pattern. When acral lentiginous melanoma progresses a combination of colours and structures appears in a multicomponent pattern.
The most specific dermoscopic finding in early acral malignant melanoma is the presence of parallel-ridge pattern that is associated to melanoma in situ. This is a distinct dermoscopic pattern that consists of a tan to dark brown pigmentation of the ridges of the skin markings, normally detected in the macular portions of melanomas in acral localizations.
In a collaborative retrospective study of the International Dermoscopy Society 167 acral lesions (66 melanomas) were evaluated for 13 dermoscopic patterns by 26 physicians. Parallel furrow pattern, bizarre pattern, and diffuse pigmentation with variable shades of brown had the highest prevalence. The agreement for lesion patterns between physicians was variable. Agreement was dependent on the level of diagnostic difficulty. In a nimber of acral lentiginous melanomas áreas with dermoscopic benign patterns were observed in combination with malignant patterns.
All these patterns are found in different ethnic groups and skin types including Caucasian population, Asian population and African population.
Schematics of the dermoscopy patterns in benign and malignant lesions. Parallel black lines represent the furrows of the volar skin markings and small white dots the eccrine duct openings.
Benign patterns*:
- Parallel furrow pattern: pigmentation following the furrows;
- Lattice-like pattern: pigmentation following the furrows plus linear bands of pigment crossing from one to the next like rungs of a ladder;
- Fibrillar/filamentous pattern: parallel fine streaks crossing the dermoglyphics in a tangential direction;
- Globular pattern: globules not associated with a parallel pattern;
- Homogeneous pattern: light brown homogeneous pigmentation with an amorphous appearance;
- Acral reticular pattern: well-defined pigment network not associated with the skin markings.
Malignant Patterns:
- Parallel ridge pattern: linear pigmentation of the ridges;
- Diffuse multicomponent pigmentation: pigmented blotches of various shades of brown observed in some portions of the lesion;
- Multi-component pattern: abrupt edge, diffuse pigmentation, peripheral irregular globules and dots, multiple colors, atypical streaks in combination with localized areas exhibiting benign patterns (fibrillar, parallel furrow or lattice-like).
- When pigmentation cannot be classified into the following mentioned groups and lack any specific features of malignancy is considered a “non-typical pattern”.
Non-pigmented tumours
A diversity of benign and malignant tumours may appear in volar skin. Amelanotic or hypopigmented acral melanoma that may account up to 34% in some series, has to be distinguished by the presence of vessels (polymorphic vessels, dotted vessels, linear irregular vessels milky red structures and hairpin vessels ), white shiny streaks (chystaline structures), ulceration and in some cases remnants of brown pigmentation.
The rule of the BRAAFF in Dermoscopy of acral melanoma
In a study of Lallas and coworkers of a total of 603 lesions (472 naevi and 131 AMs) a scoring system (named BRAAFF) composed of six variables was associated with optimal area under the curve and sensitivity for the diagnosis of AM. This method includes positive and negative predictors (furrow pattern and fibrillar pattern).
BRAAFF score (Variables associated to risk of melanoma)
A total score of ≥ 1 is needed for a diagnosis of melanoma
Positive variables
- Irregular blotch (+1)
- Ridge pattern (+3)
- Asymmetry of structures (+1)
- Asymmetry of colours (+1)
Negative variables
- Furrow pattern (-1)
- Fibrillar pattern (-1)
Management of melanocytic lesions in acral sites (volar skin)
Different authors have proposed algorithms for the management and clinical decision-making of melanocytic lesions in non-glabrous skin. These algorithms integrate clinical data such as the age, size and evolution of the lesion (congenital vs acquired; stability vs enlargement) and the dermoscopic information (acral dermoscopic patterns). With the combination of this information a more accurate management of the lesions can be concluded with the recommendation of self examination and no intervention, follow-up or skin biopsy.
In the case of melanocytic lesions with malignant patterns (parallel ridge or irregular diffuse pigmentation) partial biopsies may be insufficient to confirm a malignant lesion in early stages by histopathology due the scarce cellularity and mild atypia of the melanocytic proliferation. In these cases where the pathology can conclude a melanocytic hyperplasia without sufficient features of malignancy, the clinical-pathological correlation is needed to guide the treatment of the patient with a complete excision of the lesion.
Benign lesions simulating malignant dermoscopic patterns
In some pigmented disorders not associated to skin neoplasms can produce a parallel ridge pattern that can be indistinguishable of the dermoscopic patterns in acral lentiginous melanoma. In these situations the clinical information of age, traumatism, treatments, exogenous chemical pigmentation with paraphenil diamina or genetic disorders are the diagnostic clues. These conditions include: pigmentation of patients submitted to chemotherapy (i.e. 5 fluouracil, capacitabine), repetitive traumatism, Peutz-Jeghers syndrome or racial pigmentations in dark skin. Some of these disorders are described in this chapter.
Dermoscopy of subcorneal hematoma
Subcorneal hematoma may mimic a melanocytic lesion and dermoscopy is useful to confirm the differential diagnosis. The red-black hue is the most frequent color seen by dermoscopy (40% of the lesions) and a homogeneous pattern of pigmentation is the most frequent dermoscopic structure (53.3%). Remarkably, in a study of these lesions 40% of them exhibited a parallel-ridge pattern that is usually found in early melanoma of palms and soles. In 46.7% of the lesions, red-black globules were additionally seen at the periphery as satellites disconnected from the lesion's body. Only two lesions showed either parallel-furrow or fibrillar pattern. A scratch test performed in these lesions, may allow complete or partial removal of the pigmentation. Similarly in lesions caused by repeated traumatism due to play station manipulation has been described with a brownish pigmentation simulating a parallel ridge pattern of melanoma. In these situation the clinical history, location on the fingers symmetrically distributed and young age that is not described in acral lentiginous melanoma were the main clues for the differential diagnosis.
Dermoscopy in non-tumor skin diseases
Infections
Viral warts
appear as a verrucous, yellowish tumour with structureless area exhibiting a variable number of irregularly distributed red to brown to black dots or linear streaks (hemorrhages), which are thought to be caused by the chronically high vascular pressure at plantar sites black dots typically seen in these viral infection. These hemorrhages are a helpful criterion to distinguish plantar warts from callus due to chronic friction, which lacks blood spots, but instead typically reveals central reddish to bluish structureless pigmentation to treatments or the differential in equivocal situations. The dermatoscope has been proposed to be more sensitive for the evaluation of response to treatment when the haemorrhagic dots disappear,
Tinea nigra
This infection may produce a clinical macular brownish to grey patch with thin bundles of spicules in a parallel ridge distribution that allows the differentiation form a melanocytic lesion
Infestations
Tungasiasis has its own chapter in the dermoscopipedia. It has been described at 20-fold magnification as a typical brown-pigmented ring with a central pore that corresponds to the pigmented chitin surrounding the posterior opening of the flea exoskeleton. However tungiasis may exhibit variable dermoscopic features including blue-to-black area, structures in a radial pattern. It might be speculated that these structures correspond to eggs, but it might also be hematin in the gastrointestinal tract of the parasite.
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