Isolated areas of ­darkening skin - Clinical Advisor

Isolated areas of ­darkening skin

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  • Pigmentary demarcation lines_0912 Derm Clinic 1

A man, aged 28 years, came to the clinic complaining of skin darkening on his arms. Although he reported that this color change might have been present for a long time, his wife commented that it became more noticeable while on their recent honeymoon in the Caribbean.

Employed as an informaticist at a local medical center, he was not routinely spending extended lengths of time in the sun. The man had no significant medical history, and the only medication he took was ibuprofen on an as-needed basis following sporadic workouts.




HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 3 articles. To obtain credit, you must also read Dirty-appearing ­truncal eruption and Asymptomatic skin lesions;the post-test will include questions related to all three articles.To obtain CME/CE credit, please click here.


Pigmentation is a highly variable and diverse trait in human populations; depending on race, genetics, and environmental factors, there is a broad range of skin colors. Considerable variability is frequently found even within the same race. Furthermore, such areas of...

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Pigmentation is a highly variable and diverse trait in human populations; depending on race, genetics, and environmental factors, there is a broad range of skin colors. Considerable variability is frequently found even within the same race. Furthermore, such areas of the body as the genital region, elbows, and knees tend to be naturally darker than others.

Skin color is determined by the production of melanin in the melanocytes that originate in the neural crest and migrate to the epidermis during the second month of gestational development. Melanocytes produce and package melanin into melanophages, an intracellular organelle. A phagocytic process distributes these melanophages to the epidermal keratinocytes. Melanin granules provide keratinocytes with color and UV light protection, as they typically surround the nucleus, absorbing and reflecting UV radiation and thereby protecting the nuclear DNA from damage.

The size, number, maturity, and arrangement of melanosomes within keratinocytes ultimately determine an individual’s skin color.1 Since all races have the same number of melanocytes, color variations are related to these specific characteristics of the melanosomes.

Although genetically predetermined, skin color can vary depending on sun exposure and various physiologic conditions. Exposure to UVA light alters the oxidized state of existing melanin, causing an immediate darkening. Because this oxidized state is unstable, this darkening fades quickly. UVB light, however, causes keratinocyte DNA damage, stimulating melanocytes to produce more melanin. Melanin production takes time, so UVB exposure results in a delayed darkening, which lasts longer because it also takes time for this excess melanin to degrade.

Physiologic states of excess melanocyte-stimulating hormone can also result in more melanin production; pigmentation may be generalized (as in Addison disease) or localized (as in pregnancy), depending on the condition; hyperpigmentation of the linea nigra, genitalia, areolae, and nipples is common in pregnancy.2

A curious variation in pigmentation that is not fully understood can be seen in many normal individuals. One sees an abrupt linear transition between more- and less-pigmented skin. These pigmentary demarcation lines (PDLs) are seen most commonly on the arms, legs, chest, back, and face.2

First described in a case series of Japanese women in 1913,3 PDLs are now considered a normal variant of pigmentation and are commonly seen in people of color. Individuals of African, Indian, and Japanese descent are frequently affected, and women may be more frequently affected than men.4-7

PDLs have a variety of manifestations but most often present as a bilaterally symmetric phenomenon. Typically, PDLs become visible during the first six months of life but may be present at birth or develop during puberty. PDLs can be affected by UV light and other physiologic stimuli of melanin production, such as pregnancy.2

Five common types of PDLs (types A-E) have been described.4 Other patterns ( types F-H) have recently been described on the face in Indian patients.1 Type A is the most common and has also been referred to as Voigt lines or lines of Futcher.

  • Type A: Pigmentary change found over the upper anterior portion of arms, extending over the pectoral area
  • Type B: Appear during pregnancy on posteromedial ­portion of lower limb and typically regress postpartum
  • Type C: Vertical hypopigmented midsternal lines, extending from the clavicle to the inferior border of the sternum
  • Type D: Rare, posteromedial lines appearing along the spine
  • Type E: Bilateral hypopigmented streaks or bands over the chest in the zone between the mid-third of the clavicle and the periareolar skin
  • Type F: Hyperpigmented, symmetric, “V” shaped lines between the malar area and the temple
  • Type G: Hyperpigmented, symmetric “W” shaped lines between the malar prominence and the temple
  • Type H: Hyperpigmented, linear horizontal bands from the angle of the mouth to the lateral aspects of the chin.

The exact cause of PDLs is unknown. The observation that it occurs in 61% of family members supports the possibility that it is inherited in an autosomal dominant fashion; however, twin association has not yet been reported. The reported association with pregnancy and a higher prevalence in women support a hormonal theory.7

The color pattern of PDLs corresponds neither to Blaschko’s lines nor to a dermatomal pattern.2 Instead, the bilaterally symmetric nature suggests that PDLs follow cutaneous nerve patterns; it is speculated that PDLs exist where cutaneous innervation influences embryonic suture lines.1,5 Some theories postulate that PDLs are an evolutionary remnant (i.e., production of more pigmentation in the dorsal skin allows improved sun protection).5

Disorders that should be considered when evaluating a patient with PDLs include exogenous ochronosis, postinflammatory hyperpigmentation, Riehl melanosis, and erythema dyschromicum perstans. Exogenous ochronosis may occur paradoxically in association with the use of high-dose topical hydroquinone, a bleaching agent, and results from deposition of homogentisic acid in the skin.8

Postinflammatory hyperpigmentation is a consequence of epidermal inflammation triggering excessive melanin. Riehl melanosis, which is similar in presentation to facial PDLs, is attributable to a contact dermatitis from cosmetic use and typically resolves with discontinuation of the inciting agent.

Erythema dyschromicum perstans, sometimes referred to as ashy dermatitis, presents as blue-gray macules on the chest, head, and neck and is more frequently seen in Hispanics.

Some patients seek treatment of PDLs because of cosmetic concerns.9 Type B lines are the only category of PDLs that spontaneously regress. Use of sunscreen, avoidance of sunlight, and glycolic acid peels show only negligible change in skin color, which reverts to its previous state within months of stopping treatment.1

Very little data are available for other modes of intervention. A 2005 study reported a 70% reduction of the hyperpigmented area in a single patient treated with a Q-switched alexandrite laser.6 This laser produces photoacoustic and photomechanical destruction of the melanin-laden cells within the dermis; subsequent phagocytosis by melanophages provides melanin removal. Although potentially promising, no therapeutic options have yet shown consistent efficacy in treating PDLs.

The patient in this case required only the reassurance that this was a benign, common, and normal condition.

Amandeep Sandhu is a fourth-year medical student at Medical College of Virginia Hospitals, Virginia Commonwealth University, in Richmond where Julia R. Nunley, MD, is professor of dermatology.

References

  1. Somani VK, Razvi F, Sita VV. Pigmentary demarcation lines over the face. Indian J Dermatol Venereol Leprol. 2004;70:336-341. Available at www.ijdvl.com/text.asp?2004/70/6/336/13473.
  2. James WD, Meltzer MS, Guill MA, et al. Pigmentary demarcation lines associated with pregnancy. J Am Acad Dermatol. 1984;11:438-440.
  3. Matzumoto S. Uber eine eigentumliche Pigmentverteilung an den Voidtschen Linien (Beitrag zur kenntnis der Voigtschen Grenzen). Arch Dermatol Syph (Berlin). 1913;118:157-164.
  4. James WD, Caster JM, Rodman OG. Pigmentary dermarcation lines: a population study. J Am Acad Dermatol. 1987;16:584-590.
  5. Mintz S, Velez I. Pigmentary demarcation lines (Futcher lines): an oro­facial case. Quintessence Int. 2010;41:873-875.
  6. Bukhari IA. Effective treatment of Futcher’s lines with Q-switched alexandrite laser. J Cosmet Dermatol. 2005;4:27-28.
  7. Gupta LK, Kuldeep CM, Mittal A, et al. Pigmentary demarcation lines in pregnancy. Indian J Dermatol Venereol Leprol. 2005;71:292-293. Available at www.ijdvl.com/text.asp?2005/71/4/292/16630.
  8. Levin CY, Maibach H. Exogenous ochronosis. An update on clinical features, causative agents and treatment options. Am J Clin Dermatol. 2001;2:213-217.
  9. Kumari R, Laxmisha C, Thappa DM. Pigmentary demarcation lines associated with pregnancy. J Cosmet Dermatol. 2006;5:169-170.
  10. All electronic documents accessed August 15, 2012.

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