Infectious and Infestation Dermoscopy

01Scabies. The pathognomonic finding is the delta-wing jet with contrail: a small dark brown triangular structure (the pigmented anterior part of Sarcoptes scabiei) at the leading end of a curved or wavy whitish line (the burrow). Argenziano 1997 was the original description. Eggs and feces (scybala) appear as round structures within the burrow; their visualization supports active infestation. Diagnostic accuracy in trained hands matches or exceeds skin scraping (Dupuy 2007, Walter 2011, Park 2012). Treatment monitoring uses disappearance of the jet-with-contrail sign as a cure marker (Hamm 2006).

02Pediculosis capitis. Adult lice are seen directly as ovoid 2-3 mm structures. Nits attached to hair shafts split into three subtypes: vital nymphs (ovoid brown structures, infestation active), empty nits (ovoid translucent structures with a plane fissured free end, treated successfully), and pseudonits (hair casts, debris from spray or gel, not firmly attached, slide along the shaft). Distinguishing vital from empty nits decides whether therapy continues or stops (Di Stefani 2006, Zalaudek 2012).

03Tinea capitis. Hair shaft alterations are the diagnostic substrate. Comma hairs (short bent C-shaped hairs) reflect endothrix infection by Trichophyton or Microsporum; first described by Slowinska 2008. Corkscrew hairs (tightly coiled spiral hairs) are characteristic of African and Afro-Caribbean children and Trichophyton soudanense / T. violaceum. Zigzag hairs and Morse-code hairs (alternating thick-thin segments) round out the pattern. Black dots (broken hairs at scalp level) and yellow dots are non-specific. Combined, these signs turn trichoscopy into a chair-side TC diagnostic with high specificity, useful when KOH or culture is delayed.

04Tinea corporis. Peripheral white scale (with the free edge facing outward, opposite of pityriasis rosea), central clearing, broken or terminal hairs within the lesion, and scattered superficial fine red dots are described. The peripheral centrifugal scale is the practical clue distinguishing tinea from PR or psoriasis on the trunk. KOH still confirms.

05Tinea nigra. Superficial fine wispy light-brown strands or pigmented spicules in a reticulated pattern, on palms or soles. Distinguishes tinea nigra from acral melanoma (parallel furrow / parallel ridge patterns) and from junctional nevus (parallel furrow with consistent pigment).

06Molluscum contagiosum. Stereotypic pattern: a central pore or umbilication, polylobular white-to-yellow amorphous structures (the molluscum bodies), surrounded by linear or branching peripheral vessels (red corona / crown vessels). Especially useful in pediatric or atypical lesions and in immunosuppressed adults where presentations may be unusual (Morales 2005, Zaballos 2006, Ianhez 2011).

07Viral warts (HPV). Common warts (verruca vulgaris) show multiple densely packed papillae, each with a central red dot or loop surrounded by a whitish halo (the frog-eye pattern). Hemorrhages appear as red-to-black tiny dots or streaks. Plantar warts: prominent hemorrhages on a yellow papilliform surface where skin lines are interrupted, distinguishing from callus (intact skin lines, central reddish-bluish structureless pigment, no hemorrhages). Plane warts: regularly distributed tiny red dots on light-brown to yellow background. Genital warts: four patterns including unspecific, fingerlike, mosaic, and knoblike (Dong 2011); mosaic in flat lesions, fingerlike or knoblike in raised lesions.

08Cutaneous leishmaniasis. Generalized erythema, yellow tears (follicular plugs), hyperkeratosis, central erosion or ulceration with crust, and a polymorphous vascular pattern (commalike, hairpin, dotted, linear-irregular vessels). Translucent orange-yellow color may be present, placing CL in the granulomatous-yellow dermoscopic family. Llambrich 2009 series defined the pattern. Geographic exposure plus ulcer plus yellow tears prompts PCR.

09Tungiasis, larva migrans, tick bites. Tungiasis (sand flea Tunga penetrans): white to flesh-colored nodule with a central targetoid brownish ring around a black central pore (Bauer 2004). Cutaneous larva migrans: translucent brownish structureless areas in a segmental arrangement corresponding to the larva body (Veraldi 2000). Tick bites: anterior legs protruding from skin surface, brown-gray translucent shield (the body), pigmented streaks; post-removal, residual brown-black pigmentation indicates retained mouthparts (Oiso 2010).