Dermoscopy of mucosal lesions

INTRODUCTION — Dermoscopy, also called dermatoscopy or epiluminescence microscopy, is a noninvasive technique performed using a handheld instrument called a dermatoscope. Dermoscopy is widely used for the examination of pigmented and nonpigmented lesions of the skin, scalp, nails, palms, and soles. It increases the clinician's diagnostic accuracy and may allow the recognition of malignant skin tumors at an early, curable stage [1-7].

There is increasing evidence that dermoscopy may also be helpful for formally trained clinicians to differentiate benign from malignant or suspicious lesions arising in the mucosa and decide whether or not a lesion should be biopsied [8-13]. This topic will review the dermoscopic features of pigmented and nonpigmented mucosal lesions and the dermoscopic criteria for differentiating benign from malignant tumors. The principles of dermoscopy and the dermoscopic evaluation of skin lesions, facial lesions, and lesions of the palms and soles are discussed elsewhere.

●(See "Overview of dermoscopy".)

●(See "Dermoscopic evaluation of skin lesions".)

●(See "Dermoscopy of facial lesions".)

●(See "Dermoscopy of pigmented lesions of the palms and soles".)

●(See "Dermoscopic algorithms for skin cancer triage".)

●(See "Overview of dermoscopy of the hair and scalp".)

●(See "Dermoscopy of nonpigmented nail lesions".)

●(See "Dermoscopy of nail pigmentations".)

EXAMINATION OF MUCOSAL SURFACES — The examination of mucosal surfaces is infrequently performed during total body skin examination, due to time constraints and logistic barriers [14]. In addition, tumors in these areas may not be apparent at first glance [15]. Dermoscopy can be helpful for the examination of lesions located in the transition areas from the normal skin to the mucosa, such as the eyelids, lips, and genital and anal regions, as well as lesions located on the dorsal surface of the tongue.

Polarized dermatoscopes can be used to examine lesions with or without the need to directly contact the mucosal surface. However, for clinicians who prefer to use a contact dermatoscope to examine these areas, a practical hint for safe use is to cover the lens with a plastic food wrap or commercial cap (picture 1) [16]. Any liquid, such as disinfection spray for the mucosal region, ultrasound gel, or even water, can be put between the plastic wrap and the glass plate of the dermatoscope and between the plastic wrap and the lesion to guarantee the optimal optical conditions. When using commercial caps, no immersion fluid needs to be used between the dermatoscope lens and the cap.

HISTOLOGY OF MUCOSA AND MUCOCUTANEOUS TRANSITION ZONE — The transition areas from normal skin to mucosa show a progressive reduction of the stratum corneum, from several keratotic layers to none. With the exception of the hard palate and the dorsum of the tongue (the latter characterized by a highly differentiated, keratotic squamous layer in the form of papillae), the mucous membranes have neither a granular nor a horny layer. The underlying connective tissue, called lamina propria, is similar in structure and composition to the dermis of the skin.

In the cheek, labial, and alveolar mucosa, the interface between the mucosal epithelium and the connective tissue is relatively flat, with short papillae and wide rete ridges [17]. The transition zone between the skin and the labial mucosa, called vermilion, is characterized by a thin, keratinized epithelium, with long connective tissue papillae containing numerous superficially located capillaries, which contribute to the clinical red appearance of this structure.

The mucosa of the vulvar vestibule has a nonkeratinized superficial layer, indistinct lower layers composed of loosely packed, polygonal cells, and a basal layer [18]. The glans and the inner surface of the prepuce are lined with a variably keratinized squamous epithelium.

Melanocytes are found in the basal layer of the mucosal epithelium; however, the presence of pigmentation varies greatly between and within individuals. In individuals with lightly pigmented skin, pigmentation related to melanocyte activity is rarely seen.

DERMOSCOPIC FEATURES OF MUCOSAL LESIONS — On dermoscopy, a pigment network is rarely seen in mucosal lesions, due to the nearly complete absence of rete ridges. With the exception of the pigment network, lesions of the mucosa exhibit dermoscopic patterns similar to those seen in normal skin.

Patterns — In dermoscopy, the term pattern refers to a collection of multiple elements of the same type that covers a considerable part of the lesion. Dermoscopic patterns that can be observed in mucosal lesions include (picture 2) [19,20]:

●Lines

●Pseudopods

●Circles

●Globules or clods

●Dots

Patterns of pigmented lines can be further characterized as reticular, parallel, or curved. If none of the basic structures listed above is present, the pattern is termed "structureless."

Colors — Brown, black, blue, gray, red, purple, and white colors can be found in mucosal lesions. A given lesion may show a single color or a combination of multiple colors.

Dermoscopic-pathologic correlation — The dermoscopic-histopathologic correlates of mucosal lesions are similar to those described for cutaneous lesions [21,22]. (See "Overview of dermoscopy", section on 'Colors and structures'.)

DIAGNOSTIC CRITERIA — Because of the relative rarity of mucosal lesions examined in dermatologic clinical settings, the dermoscopic features of pigmented and nonpigmented lesions of the mucosal surfaces have been evaluated only in a few studies [8-12]. Thus, dermoscopic criteria to differentiate benign lesions from suspicious or malignant lesions are not well established, and there are no widely accepted diagnostic algorithms.

However, the International Dermoscopy Society (IDS) study suggests a simple diagnostic model based upon patterns and colors to help the clinician in the decision on whether a biopsy should be performed [10]. According to this model, the presence of blue, gray, or white color, with or without the presence of structureless areas (ie, absence of any discernible structure such as dots; globules; or clods, circles, or lines), should raise the suspicion of malignancy and prompt a biopsy for histopathologic evaluation.

In the IDS study, this model had 100 percent sensitivity and 82 percent specificity for the diagnosis of melanoma [10]. For the diagnosis of any malignant lesion, sensitivity and specificity were 93 and 82 percent, respectively. Based on this diagnostic model, even an amelanotic mucosal melanoma could be diagnosed [23].

INDICATIONS FOR BIOPSY — A partial biopsy or an excisional biopsy of a mucosal lesion should be performed in the following situations [10,24]:

●Presence of blue, gray, and white colors (either alone or combined together), especially if associated with structureless areas (picture 3A-B) [10,23]

●Unclassifiable mucosal lesion, with a history of change in the last three months [23,24]

●Patient older than 45 years with unknown history and/or an unclassifiable mucosal lesion [10,23]

INDICATION FOR DERMOSCOPIC FOLLOW-UP — In specialized dermatologic settings, a short-term (≤3 months) digital dermoscopic follow-up may be a management option for motivated, compliant patients in the following situations [10]:

●Patient with a newly detected or changing lesion without blue, gray, and white colors

●Patient younger than 45 years, with unknown history and/or unclassifiable mucosal lesion

However, it is important to maintain a low threshold of clinical suspicion to biopsy a mucosal lesion for histopathologic examination.

BENIGN LESIONS

Melanotic macule — Melanotic macule, also termed "lentigo," is the most common mucosal pigmented lesion [10]. Multiple melanotic macules are found in patients with Peutz-Jeghers or in Laugier-Hunziker syndrome [25]. (See "Congenital and inherited hyperpigmentation disorders", section on 'Peutz-Jeghers syndrome' and "Acquired hyperpigmentation disorders", section on 'Laugier-Hunziker syndrome'.)

On histopathology, melanotic macules are characterized by a basal hyperpigmentation of the epithelium without significant hyperplasia of the melanocytes. On dermoscopy, they may show a pattern of lines, dots, and/or a structureless pattern characterized by a homogenous brown color (picture 4).

Acquired melanocytic nevi — Acquired melanocytic nevi may show lines, dots, clods, and structureless areas of relatively homogenous brown color (picture 5). Rarely, gray and black colors can be present.

Congenital nevi — Congenital melanocytic nevi of mucosal surfaces typically show homogenous brownish structureless areas, sometimes associated with clods (picture 6). The features are similar to those observed in congenital nevi of the skin. (See "Congenital melanocytic nevi".)

Hemangioma and angiokeratoma — Hemangiomas and angiokeratomas show clods and/or structureless areas of red and blue colors; occasionally, lesions show white lines as a result of partial fibrosis (picture 7).

Amalgam tattoo — Amalgam tattoos are blue-black macules seen in the adjacent gingival margin or proximal buccal mucosa near amalgam dental fillings (picture 8). They are caused by the deposition in the oral soft tissues of amalgam, a mixture of silver, tin, mercury, copper, and zinc [26]. On dermoscopic examination, amalgam tattoos reveal a structureless pattern with blue, gray, or white colors (picture 9) [27]. (See "Oral lesions".)

Infectious diseases

Molluscum contagiosum — Molluscum contagiosum is a disease caused by infection with a poxvirus presenting with flesh-colored, dome-shaped papules on the skin or, rarely, on the oral mucosa [28]. On dermoscopy, molluscum demonstrates white clods with structureless areas at the periphery (picture 10). In advanced stages, crown vessels surrounding the clods may be seen. (See "Molluscum contagiosum".)

Oral papilloma — Oral papillomas are benign epithelial tumors thought to be associated with human papillomavirus infection. They present as papules or exophytic nodules with numerous finger-like surface projections. On dermoscopy, they usually show one or multiple large clods (picture 11) with or without white lines at the periphery (picture 12).

Inflammatory diseases — Examples of inflammatory diseases involving mucosal areas include lichen planus and lichen sclerosus. Whitish streaks (picture 13) are the dermoscopic hallmark of lichen, with or without zones of reddish and bluish colors representing hemorrhagic areas [29]. (See "Vulvar lichen planus" and "Vulvar lichen sclerosus: Clinical manifestations and diagnosis" and "Oral lichen planus: Pathogenesis, clinical features, and diagnosis".)

MALIGNANT AND PREMALIGNANT LESIONS

Melanoma — Early pigmented mucosal melanoma usually shows lines, dots, clods, and structureless areas characterized by a low degree of color variegation (eg, a combination of brown, gray, black, red, purple, or white) (picture 3D). Invasive melanoma shows lines, dots, clods, and structureless areas with a high degree of color variegation (picture 3A, 3C). The presence of polymorphous vessels is an important additional dermoscopic criterion for amelanotic mucosal melanoma (picture 14A-B). (See "Locoregional mucosal melanoma: Epidemiology, clinical diagnosis, and treatment".)

Bowen disease — Bowen disease is a squamous cell carcinoma in situ most often seen in older adults. On dermoscopy, the pigmented form shows peripheral dots and structureless areas with red, gray, or black colors (picture 15). The black dots at the periphery represent the vessels arranged in a linear fashion [30]. (See "Cutaneous squamous cell carcinoma (cSCC): Clinical features and diagnosis", section on 'Cutaneous squamous cell carcinoma in situ (Bowen's disease)'.)

Bowenoid papulosis — Bowenoid papulosis is a low-grade squamous cell carcinoma in situ associated with human papillomavirus infection [31]. It is most often seen in younger males and usually behaves in a benign fashion. It is characterized by multiple slightly elevated papules that are red-violet to brown-black in color. On dermoscopy, Bowenoid papulosis shows different types of lines and structureless areas with brown, gray, and black colors (picture 16).

Actinic cheilitis — Actinic cheilitis can be considered as a precursor of a squamous cell carcinoma of the lip (mostly of the lower lip). These lesions are found more often in older patients with lightly pigmented, actinic-damaged skin of the face. Clinically whitish crusts are present on the lower lip. Dermoscopically, white and red, structureless areas with few linear vessels at the periphery are visible. (See "Actinic cheilitis".)

Squamous cell carcinoma of the lip — Squamous cell carcinoma of the lip is an invasive, keratin-producing tumor of the mucosa, mostly caused by chronic ultraviolet light exposure and/or toxic damage (eg, smoking). These lesions are more often found in older patients with lightly pigmented, actinic-damaged skin of the face. Clinically exophytic crusts and tumors can be found. Dermoscopically, white and red, structureless areas with hyperkeratotic areas and polymorphic vessels (eg, comma and linear vessels with different caliber sizes) are visible.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Dermoscopy".)

SUMMARY AND RECOMMENDATIONS

●Examination of mucosal surfaces – Examination of the mucosal surfaces can be performed with either polarized and nonpolarized (contact) dermatoscopes. Contact dermatoscopes can be safely used to examine these areas by covering the lens with plastic wrap or commercial caps (picture 1). (See 'Introduction' above and 'Examination of mucosal surfaces' above.)

●Dermoscopic patterns in mucosal lesions – Dermoscopic patterns that can be observed in mucosal lesions include lines, pseudopods, circles, globules or clods, and dots (picture 2). Brown, black, blue, gray, red, purple, and white colors alone or in combination can be found in mucosal lesions. (See 'Dermoscopic features of mucosal lesions' above.)

●Benign lesions – Benign mucosal lesions include melanotic macules (picture 4) and acquired or congenital melanocytic nevi (picture 6). They are characterized by patterns of lines, dots, clods, or structureless pattern with relatively homogeneous brown color. Vascular lesions typically show clods and/or structureless areas of red and blue colors (picture 7). (See 'Benign lesions' above.)

●Malignant lesions – Mucosal melanoma is characterized by the presence of lines, dots, clods, and structureless areas, with varying degrees of color variegation (ie, a combination of brown, gray, black, red, purple, or white) (picture 3A, 3C-D). The presence of polymorphous vessels (eg, comma and linear vessels with different caliber sizes) is an important additional dermoscopic criterion for amelanotic mucosal melanoma (picture 14A-B). Squamous cell carcinoma of the lip shows white and red, structureless areas with hyperkeratotic areas and polymorphous vessels. (See 'Malignant and premalignant lesions' above.)

●Indications for biopsy – The presence of blue, gray, or white colors, especially if associated with structureless areas, should raise the suspicion of malignancy and prompt a biopsy for histopathologic evaluation. (See 'Indications for biopsy' above.)