The photographs displayed in this review article were taken and illustrated after obtaining verbal consent from the patients. Attempts have been made to ensure that the photographs do not reveal the identity of the participants.

The exact incidence and prevalence of these acquired macular hyperpigmentary disorders is unknown. Onset can occur at any age but the mean age of occurrence is usually in the 2^nd decade of life [7,8]. The condition is most common in Asia and Central and South America, as the majority of the published cases have been from those regions [7-9]. Silverberg and colleagues reported that most of the prepubertal patients suffering from Ashy dermatosis were Caucasians (52%) and Hispanics (36%) [10]. There have been two case reports of Indian children with this condition [11,12]. The condition affects both the sexes but is more common in women [7-9].

The exact cause of ashy dermatosis is unknown. However, it has been reported in association with the ingestion of ammonium nitrate and barium sulfate. The reported associated infections and infestations include hepatitis C virus infection, HIV infection and whipworm infestation [7-9].

The pathophysiology of ashy dermatosis or erythema dyschromicum perstans is currently unknown. An association with contrast agents, viral infections and worm infestations have been reported [7-9]. It has been hypothesized that an immunological response to these agents may lead to the hyperpigmentation [13]. Furthermore, Numata and his colleagues have hypothesized that a weaker immune response leads to ashy dermatosis while a stronger response can cause erythema dyschromicum perstans [13].

The only significant difference between erythema dyschromicum perstans and ashy dermatosis has been the presence of a palpable erythematous border measuring 1-2 mm in width in the early stages of the former [12,19]. However, the border can be difficult to discern in darker skinned populations [12]. A descriptive term such as macular pigmentation of uncertain aetiology should be used to describe the two conditions, which have similar clinical picture, histology and prognosis [20].

The differential generating the most controversy is lichen planus pigmentosus. In this condition, there are hyperpigmented brown macules over the exposed areas [2], which can be associated with pruritus [21,22] and with frequent remissions and exacerbations. Both ashy dermatosis and lichen planus pigmentosus are characterized by presence of pigment laden macrophages in the papillary dermis and vacuolar degeneration of the basal cells in the epidermis. Max-Joseph spaces, resulting from liquefactive degeneration of the basal layer with separation from underlying lamina propria, can observed in cases of lichen planus pigmentosus but are absent in ashy dermatosis. A band-like infiltrate present in lichen planus is absent in erythema dyschromicum perstans. However, the subpopulations of lymphocytes and keratinocytes are similar in both the conditions [2]. As a result, some authors still dispute whether the conditions are clinically and histopathologically distinct from one another [16,23].

Idiopathic eruptive macular pigmentation as the name suggests is a rare condition characterized by eruption of brownish, non-confluent, asymptomatic macules involving the trunk, neck and proximal extremities in children and adolescents [24]. The two main differences between this condition and ashy dermatosis are frequent resolution and basal layer hyperpigmentation without degeneration in the latter.

Riehl’s melanosis, a pigmented contact dermatitis to cosmetics or textiles [25,26] is characterized by reticular pigmentation, often with satellite perifollicular pigmented macules. It occurs at the site of contact, can be preceded by erythema and pruritus and patients usually demonstrate positivity to allergic patch tests [27].

An algorithm devised by Chandran and Kumarasinghe [20] can be used to make an approach to diagnosis in these conditions. The salient features are:

Lichen planus pigmentosus: Past or current evidence of lichen planus, with supportive histological features including band-like infiltrates, basal layer hyperpigmentation and presence or absence of vacuolar degeneration of basal cells [20].

Ashy dermatosis: Large macules (> 5 cm) or combination of small (< 5 cm) and large macules with grayish tinge and absence of erythematous border.

Erythema dyschromicum perstans: Large macules (> 5 cm) or combination of small (< 5 cm) and large macules with grayish tinge and presence of erythematous border.

Idiopathic eruptive macular pigmentation: Small (< 5cm) brown macules resolving in few months.

Riehl’s melanosis: Persistent small brown macules (<5 cm) that may be accompanied by erythema and pruritus and are usually caused by cosmetics and clothing.

Cosmetics and camouflage creams

These creams while not bringing any change to the lesions appear to improve the appearance of the lesions by decreasing the contrast with the surrounding uninvolved skin.

Narrow band ultraviolet therapy

Tlougan and colleagues [28] advocate the use of narrow band ultraviolet therapy. However, the recommendation is based on a single case without any mention of the dose, duration of the treatment and degree of improvement using an outcome measure.

Tacrolimus ointment

Mahajan and colleagues [29] report that in two patients with erythema dyschromicum perstans, topical tacrolimus 0.1% ointment applied twice daily to the affected areas resulted in significant improvement after 3 weeks. Controlled trials are recommended to ascertain whether the benefit is statistically significant.

Fractionated laser

Non-ablative 1550 nm fractional laser therapy was not considered to be effective for the treatment of erythema dyschromicum perstans [30]. Moreover, the therapy resulted in postinflammatory hyperpigmentation secondary to laser burns.

Clofazimine

Two studies were conducted in the last 20 years, assessing the efficacy of clofazimine for erythema dyschromicum perstans. The patients were given tablet clofazimine 100mg daily for 3 months [31,32]. The response rates varied from 66% to 87%. The side effects noted were discolourations of the skin, cornea and body fluids along with gastrointestinal intolerance. One of the reasons for not using clofazimine more often could be the drug resulting in greater dyspigmentation compared to the original condition.

Dapsone

Dapsone, another antibiotic and anti-inflammatory agent, was used by Kontochristopoulos et al. in 1998 [33]. They have reported that two patients with erythema dyschromicum perstans responded remarkably well to oral dapsone therapy at 100mg per day for three months. Subsequently, Bahadir et al. used oral dapsone therapy in one case of erythema dyschromicum perstans with excellent results [21]. However, dapsone is associated with haemolysis and fatal dapsone hypersensitivity syndrome and should be used only with caution in controlled settings.

Vitamin A

Bhutani gave Vitamin A capsules to 140 patients with lichen planus pigmentosus at dosages of 100,000 units per day for 15 days followed by rest for 15 days. Due to the large number of patients lost to follow up, it is difficult to ascertain the exact benefit of this agent in the treatment of lichen planus pigmentosus. The authors do mention that nine out of 12 patients showed good to excellent response after 10 or more courses of the drug [34].