Infectious skin diseases (Entomodermoscopy)
This chapter describes the dermoscopy aspect of infectious skin diseases
It has the following subchapters:
|Cutaneous larva migrans|
Infectious, Entomodermoscopy, Scabies, Tungiasis, Cutaneous larva migrans, Pediculosis, Tinea nigra, Demodicidosis, Molluscum contagiosum, HPV Infectious skin diseases (Entomodermoscopy) – cite! Infectious skin diseases (Entomodermoscopy) (message) Infectious skin diseases (Entomodermoscopy) – participate!
Specific dermoscopic patterns have been described for several infectious skin diseases, including those of viral, fungal and parasitic origin.
Of note, use of the new-generations dermatoscopes that do not require direct contact to the skin minimizes the risk of transfection. Interestingly, while the risk of bacterial contamination with dermoscopic examination is reported to be low, viral transmission might still represent a possible problem.
The typical dermoscopic pattern of scabies consists of small dark brown triangular structures located at the end of whitish structureless lines (curved or wavy), giving an appearance reminiscent of a delta-wing jet with contrail (Fig 9a). Microscopically, the brown triangle corresponds to the pigmented anterior part of the mite, while the burrow of the mite correlates dermoscopically to the contrail feature. Since then, the value of dermoscopy in diagnosis of scabies has been extensively investigated in several studies. The diagnostic accuracy of the technique was reported to be at least equal to traditional ex-vivo microscopic examination (i.e. skin scraping), while additional comparative advantages of dermoscopy include its non-invasiveness and lower requirements in terms of time, costs and experience. Nowadays, dermoscopy has replaced ex-vivo microscopy as the routine method for diagnosis of scabies in several dermatology centers. Additional to its value for diagnosis, dermoscopy may also be useful in treatment monitoring, heralding treatment success when dermoscopic ‘jet with contrail’ features can no longer been detected.
Tungiasis is a skin infestation caused by the sand flea Tunga penetrans and is mainly endemic in the tropical regions of South and Central America, Africa, Asia and the Caribbean Islands. Because of its low incidence outside endemic areas, its clinical features are less recognized and diagnosis may be delayed. Dermoscopy of the disease typically reveals a white to flesh colored to light brown nodule with a central targetoid brownish ring, which in turn surrounds a central (often blackish) pore.
Cutaneous larva migrans
Dermoscopy has been shown to facilitate the clinical recognition of larva migrans (creeping eruption), by revealing translucent brownish structureless areas in a segmental arrangement, corresponding to the body of the larva.
Dermoscopy allows a rapid and reliable diagnosis of pediculosis by revealing the lice itself or the nits fixed to the hair shaft (Fig 9b).Nits containing vital nymphs dermoscopically display ovoid brown structures, while the empty nits are translucent and typically show a plane and fissured free ending. This information is particularly useful for treatment monitoring, since dermoscopic detection of vital nits should lead to a continuation or modification of therapy. Additionally, dermoscopy has been recently shown to enable the discrimination between nits and the so-called pseudo-nits, such as hair casts, debris of hair spray or gel. The latter are not firmly attached to the hair shaft and appear dermoscopically as amorphous, whitish structures.
Dermoscopy has been reported to highlight the presence of tick infestation by enabling the visualization of their anterior legs protruding from the surface of the skin, while a brown to grey translucent ‘shield’ with pigmented streaks corresponds to the tick’s body (Fig 9d). Following the removal of the tick, detection of brown to black to grey areas of pigmentation by dermoscopy indicates incomplete removal.
Authors: Horacio Cabo, Emilia Cohen Sabban, Rosario Peralta.
Human demodicosis (DD) is a skin disease of the pilosebaceous units associated with human Demodex, a widely known ectoparasitic mite, involving mainly the face and head. Under dermoscopy, we observed gelatinous threads or filaments protruding out of the follicular openings known as “Demodex tails” and Demodex follicular openings that are dilated follicular openings containing round, amorphic, and yellow/light brown plugs surrounded by an erythematous halo. They are both specific features of DD. Demodicosis can be associated with rosacea and polygonal vessels to be present. The most important differential diagnoses are papulopustular or erythematotelangiectatic rosacea and seborrheic dermatitis. 
Demodex follicular openings
Common warts (verruca vulgaris) dermoscopically display multiple densely packed papillae, each containing a central red dot or loop, which is surrounded by a whitish halo. Hemorrhages represent a possible additional feature, appearing as irregularly distributed, small, red to black tiny dots or streaks. Dermoscopy of plantar warts typically reveals multiple prominent hemorrhages within a well-defined, yellowish papilliform surface, in which skin lines are interrupted. This pattern is particularly useful for their discrimination from callus, which lacks blood spots, but instead displays central reddish to bluish structureless pigmentation. Dermoscopy of plane warts typically reveals regularly distributed, tiny, red dots on a light brown to yellow background. These findings allow differentiation from acne or folliculitis, which display a central white to yellow pore corresponding to the comedo or pus within the hair follicle opening.
The dermoscopic pattern of genital warts was initially described as a mosaic pattern consisting of a white reticular network surrounding central small islands of unaffected mucosal skin. More recently, the authors of a study including a large number of patients identified 4 different dermoscopic patterns, which may also coexist in a single wart: unspecific, fingerlike, mosaic and knoblike pattern. Concerning vessels morphology, glomerular, hairpin/dotted, and glomerular/dotted vessels were detected.
Molluscum contagiosum is due to a poxvirus infection and has a characteristic dermoscopic pattern that may facilitate its clinical recognition in selected cases. Dermoscopy is especially useful in detecting the infection before the development of numerous lesions, in pediatric dermatology, or in immunosuppressed patients who may display unusual clinical manifestations. A central pore or umbilication in conjunction with polylobular white to yellow amorphous structures, surrounded by linear or branched vessels (‘red corona’), compose the stereotypic dermoscopic pattern of the disease (Fig 9c).
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