Inflammatory Dermoscopy: Psoriasis, Eczema, Lichen Planus, Pityriasis Rosea

01Plaque psoriasis. Dotted (also called coiled or glomerular) vessels are the constant feature, present in essentially every plaque. The hallmark is regular, symmetric, homogeneous distribution all over the lesion, on a light-red to salmon background, with white superficial scales. On histopathology the dots correspond to vertically arranged dilated capillary loops in elongated dermal papillae. Removing thick scale reveals tiny red blood drops, the dermoscopic Auspitz sign. Red globular rings (Vazquez-Lopez 2007) are a specific but insensitive subpattern. The pattern is preserved across body sites: scalp, palms, glans, gluteal region, face, with only the amount of scale varying.

02Eczema and dermatitis. The vessels are morphologically identical to psoriasis (dotted, sometimes coiled), but their distribution is patchy or clustered, asymmetric across the lesion. The scale is fine, often diffuse, and crucially yellow or white-yellow rather than pure white. Yellow scale is the strongest negative predictor for psoriasis in the Lallas 2012 study. The yellow clod sign of nummular eczema (Navarini 2011) describes the same finding. Yellow-orange crust corresponds to serous exudate with neutrophils, a feature shared by contact, atopic, nummular, and seborrheic dermatitis since they share spongiotic histopathology.

03Lichen planus. Wickham striae are the dermoscopic hallmark: white, often pearly, crossing or reticular streaks, present in cutaneous and mucosal LP. Their specificity approaches 100% because no other inflammatory disease reliably produces them. Vessels are mixed (dotted plus linear) and distributed at the periphery. The background is violaceous to brown-violet. Pigmentation, present in late or resolving lesions, can mimic lichenoid keratosis or regressing melanocytic lesions, so combine the vascular pattern with clinical history.

04Pityriasis rosea. The signature is a yellowish background with a peripheral collarette of fine white scale aimed inward. Dotted vessels are usually present but irregularly distributed, like in dermatitis, not regular like in psoriasis. The combination of inward-pointing collarette plus yellowish hue is the most useful clue. Herald patch and Christmas-tree distribution remain clinical signs the dermatoscope cannot replace; dermoscopy reinforces the call when distribution is atypical.

05Pityriasis rubra pilaris. Round to oval yellowish areas surrounded by mixed (linear and dotted) vessels have been reported. The data are limited (Lallas 2013 case series), but the absence of regularly distributed dots argues against psoriasis when PRP is in the differential.

06Differential algorithm in practice. Step one, vessel morphology: dotted only points to psoriasis or dermatitis; mixed points to LP or PRP; absent points to lichen sclerosus or morphea. Step two, vessel distribution: regular implies psoriasis; patchy implies dermatitis or PR; peripheral implies LP or porokeratosis. Step three, scale color: pure white implies psoriasis; yellow implies dermatitis; peripheral white collarette implies PR; absent or pearly white reticular implies LP. Step four, background: salmon implies psoriasis; yellow-tinged implies PR or PRP; violaceous implies LP.

07IDS 2020 consensus terminology. Errichetti and the IDS panel agreed on a common lexicon for non-neoplastic dermatoses: dotted, linear, linear curved (looped), linear branching, hairpin, glomerular, polygonal vessels; white, yellow, brown, orange, blue, purple, red colors; structureless areas, scales (white, yellow, brown), follicular plugs, perifollicular pigmentation, white reticular lines (Wickham striae), follicular red dots. The consensus discourages older idiosyncratic terms (red globular rings, lava lake, etc.) in favor of descriptive geometry plus color.

08Treatment monitoring. In psoriasis, dermoscopy detects involution earlier than naked-eye exam. Under biologic therapy, dotted vessels regress to punctate hemorrhagic spots before plaque flattening becomes visible (Lallas 2013). Long-term topical steroid use is detected dermoscopically as fine linear vessels (early atrophy) before clinical telangiectasias appear (Vazquez-Lopez 2004), supporting routine dermoscopic surveillance in chronically treated areas.