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Author: Professor Balachandra Ankad, Department of Dermatology, S Nijalingappa Medical College, Bagalkot-587103, Karnataka, India. Copy edited by Gus Mitchell. January 2021.
Leprosy is a chronic granulomatous disorder of the skin and nerves usually associated with Mycobacterium leprae infection.
Leprosy presents as a spectrum of disease ranging from multibacillary to paucibacillary forms. The cardinal clinical features of leprosy are hypopigmented anaesthetic patches on the skin and thickened, tender peripheral nerves.
Dermoscopic patterns in leprosy vary with the skin site/location, part of the lesion examined, and the type of lesion eg, flat versus raised.
Yellow-orange and brown-orange globules with linear and branching blood vessels which may be poorly focused. Vessels are very difficult to appreciate in flat hypopigmented extra-facial lesions.
Focal white areas and distorted pigment network with white structureless areas. Yellow-orange and/or brown-yellow globular structures with linear vessels are seen in facial lesions and raised extra-facial lesions.
Borderline tuberculoid leprosy
Focal white areas, distorted pigment network, ill-defined focal red areas with decreased white dots of eccrine and follicular openings. It is difficult to appreciate brown-yellow globules in extra-facial sites in dark skin. A pinkish background can be observed.
Distorted pigment network with reduction in white dots of eccrine and follicular openings. Focal white areas with white chrysalis strands are usually seen. Brown-yellow globules are not easily appreciated. White rosettes have been described in facial lesions and are non-specific, being seen in many other conditions.
Borderline lepromatous leprosy
Distorted pigment network with chrysalis strands and prominent linear and branching vessels are seen in nodular lesions. Vascular elements are not obvious in patches. Globules are difficult to find.
White structureless areas with linear and branching vessels running towards the centre of the lesion, so-called crown vessels. White chrysalis strands and peripheral brownish pigment are typically seen.
Prominent skin lines with white scale and changes in the pigment network.
Pure neural leprosy
Focal white areas and broken pigment networks correspond with decreased basal layer melanin and flattening of rete ridges respectively. The decrease in white dots is due to a reduced number of follicular and eccrine structures. Granulomas are seen particularly on skin biopsy of the tuberculoid forms of leprosy, and are responsible for the brown-yellow globules. Linear and branching vessels are dilated capillaries. White chrysalis strands correlate with dermal collagen [see Leprosy pathology].
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