Monday, May 21

Mongolian blue spot birthmark - Dermal Melanocytosis

Blue skin discoloration > Mongolian spot
Also known as Congenital Dermal Melanocytosis, Mongolian blue spot, is a benign asymptomatic birthmark present at birth or appears shortly thereafter. It is also known as Mongolian spot and Mongolian birthmark.
This pigmented macule is flat and irregular in shape with wavy and indistinct border. Mongolian condition is usually present as multiple patches or one single large patch in lumbosacral area and buttocks; it may also occur on shoulders and other parts of the body, usually sparing head, face, palms and soles.
Picture of blue skin coloration Mongolian blue spot

image by: Flickr/mliu92/CC BY-NC-SA 2.0

   The Mongolian spot spontaneously regresses, fades and disappears by the age of 3 or 4 years. It rarely persist up to puberty. As this macule is harmless and disappears on its own, no treatment is necessary. Blue and blue-green are the most common colors. However grey, slate-grey, blue-grey, grey-black and brown coloration are also encountered.

   This Mongolian condition is congenital in origin and involves skin. The blue skin discoloration is due to dense presence of melanocytes, the pigment cells containing melanin. Though normally melanocytes are present in epidermal layer of skin, in these Mongolian spots, they are present in deeper dermis layer of skin. Histological studies reveal the presence of widely placed dendritic melanocytes in lower reticular dermis. These melanocytes are found between bundles of collagen. In contrast to blue nevus wherein the dermis is fibrotic, the collagen is unaltered in Mongolian spot.

   Erwin Bälz (13 January 1849 – 31 August 1913) discovered and named "Mongolian spot". He was a German and was a personal physician to the Japanese Imperial Family. He was the founder of modern medicine in Japan. He thought that the blue macules found in Japanese babies are characteristics of the Mongoloid races and called them Mongolian spots.

However Mongolian macule is highly prevalent among people of East and South-east Asian origin, East Africans and Native Americans (85-100%). People of Turkish and Hispanic origins also have high degree of prevalence (50-70%). It is rarer among Caucasian (1-10%) and other races. Mongolian pigment condition is unrelated to gender and both female and male infants are equally predisposed. Sometimes Mongolian spot may be mistaken for bruise due to child abuse.

Neural crest, melanocytes and Mongolian spot

   A brief knowledge of fetal development is necessary for understanding how Mongolian blue spot is formed. During gastrulation stage, fetus undergoes massive reorganisation by the processes called invagination, ingression and involution. From being a spherical ball of cells (blastula) it is transformed into multilayer  organism. Now a neural plate is formed by thickening of the ectoderm layer. The edges of the plate fold and raise to meet at the middle to form neural tube and epidermis. the cells at the tips of the neural folds and adjoining epidermis form neural crest cells.

   Neural crest is a pluripotent population of transient cells with multiple fates. They detach and migrate extensively throughout the fetus. Stopping at different locations, these pluripotent cells give rise to a wide array of derivatives. Some of these cells become melanocytic progenitors, getting restricted to melanogenic lineage, due to the process of melanoblast specification by various transcription factors and extracellular signalling pathways. These melanocytic progenitors are also known as melanoblasts and are unpigmented. However they have potential to produce melanin. During their migration from neural crest to epidermis, some of these melanoblasts get entrapped in dermis layer, transform to melanocytes and start producing melanin. The melanin pigment in deeper dermal areas of skin gives the blue colored appearance of Mongolian spot.
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