JAMES M.GRICHNIKMD, PhD
Melanomas often have an ominous appearance. The trained eye is preferentially drawn to them. Sometimes the best clues to the diagnosis are not in the peculiarities we visually appreciate, such as variegation of color, border irregularity, and size, but in the subtleties that we may not fully appreciate.
Careful scrutiny of these lesions over the last 40 years has made me aware of an aberration that may support the clinical diagnosis of melanoma. There is often a peripheral zone of clearing surrounding the entire lesion of 1 cm or more. The pigmentation may be a shade lighter but not to the extent seen in halo nevi. The skin markings within the zone are those of normal skin; the lentigenes, ephelides, and telangiectasias that are easily found beyond the outer margin of the zone are often not found within it. The phenomenon may be likened to a β-hemolytic streptococcal colony growing on blood agar. The hemolytic toxin produced by the colony has diffused beyond the margin of the colony destroying all the red blood cells it encountered. Possibly melanoma cells are doing something very similar.
Lloyd KM. The Peripheral Clearing ZoneSometimes a Subtle Clue for the Recognition of Melanoma. Arch Dermatol. 2006;142(12):1676. doi:10.1001/archderm.142.12.1676