Dermatoscopy: A New Diagnostic Approach for Lesions on Mucous Membrane

Abstract

Dermatoscope is used to examine the skin lesions without obstruction and is known as dermatoscopy or epiluminescence microscopy. Similarly, dermatoscope can be used to examine lesions on the mucous membrane of oral cavity. This is termed as “mucoscopy”. Mucoscopy is an important upcoming digital tool for oral mucosal disorders. It can help to distinguish between the benign and malignant lesions, but needs to be correlated with clinical and histopathology if required. As literature on mucoscopy is minimal and is limited to individual case or case series. An organized, systemic analysis is very much essential on this topic. This chapter would focus on mucoscopic features of certain oral lesions which would help with further development and improvement of a non-invasive technique for diagnosis.

1. Introduction

Skin surface microscopy was introduced in 1663. Later a German dermatologist named Johann Saphier, added a light source as an improvisation to the device. The word “Dermoscopy” was coined first by a dermatologist named Goldman. Further, many universities, along with physicians and device manufacturing companies invented and patented many additions to the basic instrument [1, 2].

Dermatoscopy is a non-invasive and in vivo technique to appraise the pigmented skin lesions with a hand-held instrument or device termed as dermatoscope. However, it can also be used to examine lesions with little or no pigmentation [3]. The synonyms for this technique are Dermoscopy, epiluminescence microscopy, incident light microscopy, and skin-surface microscopy [4].

A dermatoscope is composed of an illuminating light source and a magnifying lens. The light source here can be nonpolarized or polarized. Polarized and nonpolarized light is combined with the magnifying lens and can be used as a surface contact or non-contact device [5, 6]. With this permutation and combination there are four types of dermatoscopes, they are

1. Polarized light, contact

2. Polarized light, non-contact

3. Non-polarized light, contact

4. Non-polarized light, non-contact

This device magnifies the structures or details that are not visible to the naked eye in the sub-dermal region of the epidermis, by 10 times for easy visualization. This magnification increases up to 70–80 times with a video recorder. Specialized add-ons like FotoFinder device (magnification up to 140×), camera attachments (magnification up to 400×) are available along with dermatoscope to capture images or recordings for storage or serial analysis [5, 7].

When dermatoscope is used to assess the mucosal surface is termed as ‘mucoscopy’. However, the literature on mucoscopy is limited. Though observation of mucous membranes should be part of a dermatological examination usage of this device in mucoscopy is negligible. However, recent studies have shown that the potential of this instrument in mucoscopy. The aim of this chapter was to summarize the use of this device on mucous membrane [8].

2. Basic science of dermatoscope

When we use a device, knowing the science behind its working is of prime importance. Normally when a visible light falls on an object, it is either reflected, scattered, or absorbed by the object itself. If we consider skin as the object on which light falls, most of the light is reflected due to the increased refractive index of the stratum corneum (1.55) when compared with refractive index of air (1.0). Reflection from skin surface can be reduced by fixing a glass plate with refractive index 1.52 Figure 1 and using an immersion fluid as an interface or by using polarizing filters Figure 2 [9, 10].

Figure 1.

Shows the working of a dermoscope using a glassplate with an immersion fluid.

Figure 2.

Shows the working of a dermoscope using cross polarization.

Numerous immersion fluids like alcohols, water, oils and gels have been used. Most commonly used immersion medium being the alcohol (ethanol 70%) due to its low viscosity, amphiphilic solubility, disinfectant capability and image clarity. But in mucoscopy water soluble gels are preferred over alcohol because of their non-caustic property and higher viscosity [11]. Air bubbles along the immersion medium can hinder the clarity of structures under examination, because it creates a skin-air interface. It is very important to remove all the air bubbles before examination.

Another method to reduce the reflection from the assessing surface is by using polarizing light. In polarized light dermatoscope two filters are placed perpendicularly. When it reaches the surface of skin/mucous membrane, part of polarized light is scattered from surface and other part is scattered from deeper layers. The light reflected from surface causes glare, therefore is blocked by one of the attached filters. The light reflected by deeper layers is backscattered and makes it visible to the eye. This technique, which allows the light which has lost its polarization to pass through the second filter with additional blocking of the reflected light which maintains its polarization is known as “cross-polarization” [10, 12].

2.1 Language of dermatoscopy

To acquire complete knowledge for using dermatoscopy on mucous membrane we need learn certain basic elements in this field. These elements are very important to describe and diagnose a skin/mucous lesions [13, 14].

A list of basic elements is as follows, Figure 3:

1. Lines (these straight objects present on the lesions which are longer in length than its width)

2. Globules (irregular objects with definite size and shape, easily identifiable due to its large size)

3. Pseudopod (one sided Dumble shaped)

4. Dots (shape is similar to globules, but are smaller in size)

5. Circles (ring like margin, which has a same center)

6. Structureless areas or blotches (any pattern of area which do not contain any definable above described objects)

Figure 3.

Schematic diagram showing the basic elements of dermatoscopy.

There are certain terminologies used to describe a vascular component of a lesion, Figure 4 [15].

1. Comma-shaped vessels

2. Perifollicular network of vessels

3. Dilated linear vessels

4. Doted blood vessels

5. Linear branching

6. Linear vessels with loops at their ends (hairpin vessels)

Figure 4.

Schematic diagram describing the vascular components seen in dermatoscopy.

Other than these basic elements dermatoscopic lesions are evaluated on colors and harmony. Colors recognized are black, dark brown, orange, pink, white, gray, steel blue, purple, red and yellow [16]. With the knowledge of these basic elements of dermatoscopy we move ahead to describe known mucoscopic features of oral lesions.

3. Description of mucoscopic features of oral lesions

3.1 Fordyce’s spots

These can be seen in any part of the oral mucosa due to presence of ectopic sebaceous glands. Mucoscopy shows whitish to yellowish separate round to oval structures corresponding to sebaceous glands with central opaque globules with small openings. These are surrounded by linear branched vessels [17].

3.2 Lingual varicosities

The sublingual veins in which there is degeneration of proteins in their elastic tissues are called as lingual varicosities. This is seen most frequently on the ventral surface of tongue. Mucoscopic features can be described as linear distribution of dark blue to black dilated vessels along with white shiny blotched areas [18].

3.3 Mucocele

This is the most common salivary gland cyst. It presents in two types based on the collection of mucus. Due to trauma if the salivary gland duct is severed and mucus collects in the connective tissue, then it is called extravasated type of mucocele. If the mucus is collected within the duct due its obstruction, then it is named as retention type of mucocele [19]. Mucoscopic features for this cyst is described in three different types [20].

Type I (retention/extravasated mucocele): purple in color and branched network of vessels.

Type II (due to recurrent trauma mucocele is associated surface hyperkeratosis): hyperkeratotic white areas with small unclear looped vessels.

Type III (lack of mucin material, healing stage): red in color, with yellowish areas and clear linear vessels with looped ends (hairpin vessels) [21].

3.4 Lichen planus

Lichen planus is considered as one of the potentially malignant disorders and a common mucocutaneous disease. In most of the lichen planus cases, oral lesions help in the early diagnosis of this disease, as they precede the skin lesions. Lichen planus has different clinical appearances and are described as—radiating white to gray, velvety, reticular patches, rings or streaks, thread-like or lacy papules in linear, annular or reticular forms [19]. Generally, symmetrical skin lesion is considered to be benign and asymmetrical as malignant. Sometimes odd shaped or irregular shaped lesions can also be benign. This holds good for mucosal lesions too [16]. Mucoscopy shows white reticular lines over a pink to purplish background. Sometimes crusts or scaling might also be seen in lip lesions. Tongue lesions display more curved vessels along with the above features. Dark skinned patients present a tricolored background (white + brown + red). Tiny erosions, globules, dots and mixed vascular pattern can be additional features depending on their clinical presentations [22].

3.5 Granular cell tumor

This is a benign tumor of neural origin (schwann cells). This tumor can be seen in any part of the body and in any age group, but more than half of the cases is seen in the oral cavity. Among the cases presenting in the oral cavity, more than one third are seen on lingual dorsum [19]. Yellowish to white structureless areas with surrounding polymorphic vessels are seen in mucoscopy, but the data are scant [23].

3.6 Pyogenic granuloma

This originates as a response of the tissues to nonspecific infections, therefore it’s considered as reactive lesion. Three structures are mainly seen in the mucoscopy of these lesions—white linear lines representing the intra lobular fibrous septa, red homogenous areas and white area in a collar like fashion corresponding to hyperplastic epithelium [24, 25].

3.7 Haemangiomas and vascular malformations

Haemangiomas are tumors characterized by rapid endothelial cell proliferation, whereas vascular malformations results from anomalous development of vascular plexuses with normal endothelial cell growth cycle. Mucoscopic pattern of haemangiomas showed red pseudopods with network of white lines. Vascular malformations show thick elongated linear red or brownish lines in contrast to haemangiomas [26].

3.8 Anomalies of tongue

3.8.1 Black hairy tongue

The basic defect in hairy tongue is hypertrophy of filiform papillae. Typically, they are 1 mm in size, while filiform papillae in hairy tongue are greater than 10–15 mm in size. Generally, the condition is referred as black hairy tongue, however, the color may vary (brown, white, green or pink) depending on the etiology and secondary factors [19]. Mucoscopic features show brownish hairlike elongation of filiform papillae which are interspersed with white fungiform papillae [17].

3.8.2 Benign migratory glossitis

It is a psoriasiform mucositis with a characteristic feature of constantly changing pattern of white serpentine lines and surrounding areas of smooth and depapillated mucosa [27]. Under mucoscopy, reddish areas due to atrophy of filiform papillae and white lines demarcating the unchanged areas are seen [28].

3.8.3 Median rhomboid glossitis

This is a developmental anomaly of tongue because it is seen due to defective midline fusion of two lingual swellings and posterior fusion of tuberculum impar, leaving a rhomboid shaped smooth erythematous area. Features under mucoscopy shows desquamated or absence of lingual papillae and periphery of the lesion shows presence of normal papillae [28].

3.9 Aphthous stomatitis

This is a very common multifactorial disease with solitary or multiple painful ulcerations. Clinically these ulcers with gray membrane, necrotic centre and raised margins surrounded by erythematous halo [27]. Mucoscopically, yellowish to red central part encircled by a whitish structureless region and a circular edge of erythema [4].

3.10 Irritational fibroma

It is formed by the focal hyperplasia of connective tissue as a reaction to the induced trauma or irritation in the oral cavity. Dotted and irregular vessels are seen on a pinkish colored background under mucoscopy [29].

3.11 Pigmented lesions

The common pigmented lesions on oral mucosa are labial pigmented/melanotic macule, mucosal melanosis and physiological gingival melanin hyperpigmentation. Mucoscopic features of pigmented melanotic macule are reticular or parallel linear lines (including hyphal or fish-scale variants), dots or globules on surface, structureless area. In case of ephelides seen in Peutz-Jeghers or Addison disease we notice brownish, intertwined network “moth-eaten” borders or thick reticular lines with grayish granules or globules [30, 31, 32]. In case physiologic pigmented gingiva the mucosopic features is simply a homogenous brownish structureless area [33].

Amalgam tattoo is also one of the common pigmentations seen in the oral cavity. These pigmentations are seen as radio-opaque areas on radiographs [34], but mucoscopy shows structureless, homogenous, grainy, bluish pattern [35].

Oral melanoacanthoma also present as brown/black well-circumscribed macules or papules which may increase in size up to few centimeters [36]. Their starburst pattern with symmetric pigmented streaks along the lesion’s periphery under mucoscopy can differentiate them from Peutz-Jeghers or Addison disease [35].

Melanocytic nevi are well defined macules. They can be congenital or acquired. They are classified as junctional, compound and intradermal/intramucosal. Mucoscopy of these macules show structurally homogeneous with wide or noticeable pigment network and streaks [34].

3.12 Cheilitis

It is a multifactorial disease affecting the lips. Due to varied aetiological factors the clinical presentation also varies, similarly the features under mucoscopy. Lesions associated with ulcerations presented with yellow to red structureless areas, fibrillar network. In allergic cheilitis yellowish to white scale and pinkish white structureless areas along with dotted vessels were evident. Few additional features to the later can be large red globules or scattered dotted vessels [37].

3.13 Squamous cell carcinoma

Squamous cell carcinoma (SCC) is the second most common malignancy. Even though the gold standard of diagnosis for squamous cell carcinoma is biopsy trailed by histopathological evaluation, non-invasive diagnostic tools have found increased attention. Dermoscopy has become one of the basic diagnostic methods in clinical practice. The most common dermoscopic features of non-invasive squamous cell carcinoma include clustered vascular pattern, glomerular vessels and hyperkeratosis [38]. Whereas invasive squamous cell carcinoma presents with a vascular polymorphism comprising of linear irregular, hairpin and grouped glomerular/dotted vessels over a whitish background with a central core of keratin or ulceration [39].

The clinic-dermoscopic-pathologic correlation can be shown with white-colored criteria, including scales/keratin, white circles, white halos and structureless whitish areas in well- or moderately differentiated variant. Whereas in poorly differentiated SCCs predominantly red color is seen which results from the presence of bleeding and/or dense vascularity, in the absence of scaling and keratin or other white-colored criteria. A diffuse distribution of vessels in various patterns and bleeding are signs of poor differentiation, while scaling is indicative of well- or moderately differentiated SCC [40]. Keratoacanthoma is a common low-grade tumor which closely resembles SCC microscopically. The most important dermoscopic features to keratoacanthoma and SCC are white circles, keratin crust/scale, blood spots, and white structurless zones. White circles are more common in SCC and keratin crust/scale in keratoacanthoma [38].

4. Conclusion

The dermatoscope has gained incredible popularity among dermatologists as an adjunctive tool to better visualize subsurface structures and identify patterns that may improve the diagnosis of a wide range of skin diseases. Similarly, mucoscopy should also be developed by analyzing many more cases on each above stated entities to confirm and support the findings. Difficulties in mucoscopy like hard-to-reach areas, contamination of instrument, conditions in which mouth opening difficulty is seen and cost effectiveness have to be encountered. The future of dermatoscopy/mucoscopy will involve combination of artificial intelligence that will make the assessment process increasingly objective, more accurate, and universally available. Despite the use of use dermatoscopy long, its widespread use on mucous membrane still remains unclear, whether it has decreased biopsy rates of benign lesions, reduced health care costs, or improved patient outcomes.