Facial melanoses affecting the face and neck region are of considerable concern to darker-skinned people. Although many facial melanoses, such as melasma, are well defined clinically, rendering them easy to diagnose, others have overlapping clinical morphology as well as histopathology. Riehl melanosis (RM), commonly considered as a pigmented contact dermatitis (PCD), is one such condition with diverse yet overlapping clinical features with other facial melanoses as ashy dermatosis and lichen planus pigmentosus.
RM is best defined as an acquired low-grade allergic contact dermatitis to fragrance and other cosmetic products that presents with abnormal hyperpigmentation involving the face and neck regions. The disorder is known to predominantly affect patients of Asian descent.
Historical Aspects of Nosology of Riehl Melanosis
During the first world war, Riehl first identified several patients of both genders with striking dark brown to grayish-brown pigmentation on the forehead, temporal, and zygomatic regions of the face. The involved skin was mildly indurated with a rough texture and appeared to mildly scaly without any erythema or atrophy. The pigmentation was diffuse and uniform but without well-defined margins. It extended to the ears and neck, with gradual fading off towards the chest as small discreet pigmented follicular-based macules. Other body parts like the axillae, arms, and forearms, submammary and umbilical regions also showed similar pigmentation, but it was much lighter than the face. Riehl was uncertain about the etiology, but he suggested wartime food substitutes, mainly poor-quality flour, as being contributing factors. The condition seemed to have disappeared, with no cases reported towards the end of the war.
Later, similar cases were described from different centers. Hoffmann and Habermann emphasized that local chemical irritation due to the use of certain oils and hydrocarbons were responsible for melanosis similar to Riehl melanosis and labeled it 'melanodermatitis toxica.' However, this entity was not accepted by Riehl. The term "Riehl melanosis" became popular in the period between the two World Wars for facial melanosis caused by external chemical agents. During the Second World War (1945-1948), 165 new cases of suspected RM were diagnosed in Vienna with a female predominance. This condition disappeared again with the end of the war. Since then, RM was reported from many centers across the globe, especially from France and Argentina.
The inflammatory component of the early phase of RM was strongly suggested by Miescher and was confirmed on histology in 200 cases by Joulia et al. in 1950.
The etiology of RM was unknown until the late 1940s and 1950s when two studies from Argentina by Pierin et al. and Puente et al. attributed facial pigmentation similar to RM to cosmetic ingredients, typically aniline dye (orange II) found in facial powder. Positive patch tests to the dye were supported by the disappearance of early inflammation and progressive reduction in pigmentation on discontinuing the use of the facial powder.
In 1970, the term "pigmented contact dermatitis" was coined by Osmundsen, a Danish dermatologist who documented several cases of peculiar facial hyperpigmentation in Copenhagen. Investigation revealed that hyperpigmentation was the result of contact dermatitis to an optical whitener, Tinopal CH 3566, in washing powder.
Subsequently, in 1973, the term pigmented cosmetic contact dermatitis was introduced by Nakayama, a Japanese dermatologist, for cases that were ascribed to cosmetic contact allergens especially Brilliant Lake Red R.
To date, the etiology of RM is still controversial, although the majority of experts consider it synonymous with PCD of the face. However, a recent global consensus statement emphasized that finely reticulated hyperpigmentation on the face and neck region should be labeled “pigmented contact dermatitis” rather than RM if its appearance is preceded by contact allergy. If etiology is uncertain, the term RM should be used.
The etiology of Riehl melanosis remains controversial, whether it is associated with intrinsic or extrinsic factors. The majority of cases occur clearly because of exogenous factors, leading the authors, as described below, to label it contact dermatitis. It usually results from direct contact with several allergens. However, few cases secondary to contact with airborne allergens have been also described. UV exposure may play a role in some PCD since hyperpigmentation is often photo-localized, and some of the causative chemicals are known photosensitizer.
Other allergens had also been described like Plathymenia foliosa (wood dust; airborne allergen), minoxidil 5%, chromate (leather, soap), and nickel sulfate (metal product).
Nevertheless, a few cases due to endogenous factors have been also described such as nutritional effects suggested by Riehl, toxic factors, neurovegetative lability, and digestive disorders. Besides, Riehl melanosis–like eruption had been reported in Japanese women as a cutaneous manifestation of Sjögren syndrome caused by the development of anti-SSA (Ro) antibodies. Pigmentation gradually disappeared when the patient avoided sun exposure. Cosmetics and detergents had not been interrupted.
Repeated contact with low concentrations of these allergens explains why they do not provoke an eczematous reaction in the middle of the spinous cell but instead, their accumulation induces type IV allergic cytolytic reactions in the basal layer.
The incidence is not known. Riehl melanosis is more common in darkly pigmented races. Young to middle-aged women are the most concerned group. However, men and children could also be affected by PCD. A large proportion of reports are from Japan, cases have been described as well in Europe, South America, India, and South Africa.
Most biopsy results have shown interface dermatitis. Riehl melanosis presents, in early lesions, with vacuolar basal layer degeneration, perivascular or band-like dermal lymphohistiocytic infiltrate, and dermal pigmentary incontinence. At a later stage, histologic examination shows rather upper dermal melanophage infiltration. The direct immunofluorescence study is negative.
Riehl melanosis typically presents as patchy to diffuse pigmentation, often with a slightly scaly skin surface and satellite pigmented follicular-based macules. The reticular pattern is often observed at the center of the pigmented areas.
Some patients complain of erythema, edema, and pruritus preceding the occurrence of the pigmentation. This inflammatory phase suggests the onset as an ordinary contact dermatitis caused by allergens when came into contact with the skin.
Sites of involvement are variable, depending on the allergen responsible. Pigmented cosmetic dermatitis involves usually the face (forehead, zygomatic and temple regions), whereas textile contact dermatitis more often involves axillary borders; sparing the vault. When the allergens implicated are photosensitizers, the pigmentation is more pronounced in sun-exposed areas.
Dermoscopy may represent a non-invasive aid to clinical diagnosis of Riehl melanosis. The most common observed findings are pseudonetworks, gray dots or granules, and telangiectatic vessels.
Reflectance confocal microscopy correlates with the conventional histopathologic examination and may show pigment incontinence, mildly refractive cells corresponding to infiltrated lymphocytes, dilated vessels, and features of basal layer liquefaction including obscured papillary rims, total or partial obliteration of the ring-like structures around the dermal papillae.
Patch testing is recommended in diagnosing RM. Closed patch testing should be performed with standard series, cosmetic series, fragrance series, and patient’s products. If photoallergy is suspected, photo-patch testing should be carried out. Patch test sites may show papule, vesicle, or brown pigment. Given the low concentration of the allergen in cosmetic and fragrance series, repeated open application test (ROAT) are needed if closed patch testing is negative or equivocal. If ROAT performed on the flexor forearm skin is equivocal, the patient’s product could be applied to the face or other affected areas.
Skin biopsy is not required unless there is an atypical clinical presentation.
Treatment modalities for RM are as follow :
A recent study showing the higher effectiveness of mid-fluence QSNY 1064-nm laser in targetting the deep pigmentation of RM has also been conducted.
A combination of therapies should be considered for recalcitrant forms. Recently, a significant improvement of RM had been reported with a triple combination of salicylic acid peels, oral glycyrrhizin compound, and vitamin C.
Another study used a combination of therapies to include low-fluence, 1064-nm, Q-switched Nd: YAG laser, hydroquinone cream, and oral tranexamic acid, with the majority of patients experiencing significant improvement.
Various diseases can mimic Riehl melanosis.
Histologically, these diseases are marked by a lichenoid reaction, added the other characteristic findings.
Others Differential Diagnosis
Patients shall be educated about the importance of these general instructions:
Currently, Riehl melanosis is considered as a non-eczematous allergic contact dermatitis to fragrance, cosmetics, and sometimes occupational agents. It is specially marked by a reticulate gray-brown to black pigmentation involving the face and neck, interface dermatitis, and pigment incontinence. Hence, the diagnosis is best reached with an interprofessional team including dermatologists, pathologists, pharmacists, and occupational physicians. The goal of treating patients is aesthetic.
Fortunately, RM may resolve gradually on its own when the triggers factors are removed. Hence, healthcare workers including primary care physicians, pharmacists, dermatologists, and nurse practitioners, should educate the patient on avoiding the suspected allergen and sun exposure.
The outcomes for most patients are unpredictable. The condition is known to cause psychosocial impact, and hence a mental health counselor should be consulted.
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