What is Riehl melanosis (pigmented contact dermatitis)?

Updated: May 27, 2021
  • Author: Elizabeth K Satter, MD, MPH; Chief Editor: William D James, MD  more...
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Answer

Cutaneous hyperpigmentation is a frequent dermatologic complaint, which most commonly affects people with skin of color (Fitzpatrick types III-VI) around the world, and often these conditions have an enormous negative psychosocial impact. [1] Until recently, there has been no consensus regarding the terminology used to describe a variety of possibly interrelated acquired macular dermal hyperpigmentation disorders of unknown etiology, including ashy dermatosis (AD), lichen planus pigmentosus (LPP)/lichen dyschromicum perstans, erythema dyschromicum perstans (EDP), and idiopathic eruptive macular pigmentation. [2] Although many people have also included Riehl melanosis within the aforementioned categories of acquired pigmentary disorders, in 2018 the international pigmentary consensus meetings determined that Riehl melanosis is better classified as a separate entity because the clinical presentation slightly differs and it is hypothesized to arise as a result of contact dermatitis. [3]

In the spring of 1917, during World War I, Riehl first identified 17 patients with striking dark-brown to grayish-brown facial pigmentation, which was most pronounced on the lateral aspects of the face and neck and primarily concentrated on the forehead, ears, temple, and zygomatic regions. [4, 5] Hyperpigmentation was also noted on the thorax, but it was less pronounced in this region and primarily consisted of small follicular-based pigmented macules. Subtle hyperpigmentation was also identified on the hands, forearms, and intertriginous regions. [5] The patients ranged in age and sex, but all were White from Vienna and without evidence of an underlying illness. In addition to hyperpigmentation, erythematous macules and papules were also identified. [5, 6, 7] Histologically, the lesions were marked by a dense inflammatory cell infiltrate in the superficial dermis admixed with melanophages. [5, 6]

Although Riehl was unable to identify the cause of the eruption, he speculated that the etiology of hyperpigmentation was a nutritional alteration attributed to wartime conditions. [4, 5, 6, 7] Concomitant with the end of the war, no further cases were identified, thereby supporting his hypothesis. [5] Subsequently in World War II, a similar eruption surfaced in approximately 165 people in France, again this was associated with the scarce food supplies and disappeared with the end of the war; however, this latter situation differed from what had been previously seen in World War I in that the majority of cases were reported in women. [5, 6]

Later, Hoffmann and Habermann described a condition referred to as melanodermatitis toxica and hypothesized that it may represent a type of contact dermatitis associated with the use of certain oils and hydrocarbons. Although these authors emphasized the clinical similarities between Riehl melanosis and melanodermatitis toxica, Riehl could not accept that the melanosis he described was due to a local chemical irritant and thought the conditions were separate entities. The role of nutrition as a possible cause of this unusual melanosis was further addressed in a paper by Findlay, who described several cases of Riehl melanosis in the Bantu people in South Africa; however, no further reports in the literature linked Riehl melanosis to nutritional deficiencies. [8]

Subsequent to the great wars, the majority of cases of Riehl melanosis described in the literature differ from the cases originally described by Riehl. In 1950, Minami and Noma described a pigmented dermatitis in Asian women unrelated to the war and named the condition melanosis faciei feminae. [6] The etiology of this latter pigmentation was unknown for many years, until 2 studies from Argentina in the late 1940s and 1950s described facial pigmentation similar to Riehl melanosis that was subsequently attributed to the use of cosmetics. In the first study, patch testing identified aniline dye (orange II) present in facial powder as the cause of the pigmented contact dermatitis, whereas the second study emphasized that photosensitizing may play an addition role in the pigmentation. [5, 9]

In 1970, Osmundsen subsequently reported 7 patients who had a similar bizarre hyperpigmentation that occurred as a result of contact dermatitis to an optical whitener, Tinopal CH 3566, in washing powder and called the condition pigmented contact dermatitis (PCD). [10] Subsequently in 1973, Nakayama introduced the term pigmented cosmetic contact dermatitis for cases that were ascribed to the use of certain cosmetics.

To date, the etiology of Riehl melanosis remains controversial, and although the majority of experts believe it is synonymous with pigmented contact dermatitis, some authors insist that this is an erroneous assumption because the cases reported by Riehl appear to have been related to nutritional alterations that arose during World War I, with no further case reports noted after the war ended, and thereby insist that Riehl melanosis should be classified as a distinct entity. [4, 5, 6, 7] Pigmented contact dermatitis, on the other hand, is caused by an allergic contact dermatitis to a variety of topical and airborne allergens or a lichenoid immune reaction that may be caused by intrinsic or extrinsic factors. [11, 12]


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