What is idiopathic eruptive macular hyperpigmentation?
Idiopathic eruptive macular hyperpigmentation is a rare benign pigmentary disorder of the first two decades of life characterised by asymptomatic hyperpigmented macules with a predilection for the upper body regions . It is classified as a variant of acquired dermal macular hyperpigmentation.
Who gets idiopathic eruptive macular hyperpigmentation?
Idiopathic eruptive macular hyperpigmentation can occur in any age group and affects both sexes. However most reported cases develop in children and adolescents .
What causes idiopathic eruptive macular hyperpigmentation?
The cause of idiopathic eruptive macular hyperpigmentation is unknown. The hypermelanosis occurs sporadically in the absence of preceding illness, inflammation, sun exposure, or medication . It has not been reported to be familial .
Hormones have been hypothesised to play a role in rare cases that have worsened during pregnancy .
What are the clinical features of idiopathic eruptive macular hyperpigmentation?
Idiopathic eruptive macular hyperpigmentation is characterised by multiple discrete asymptomatic brown-grey-black small macules or larger patches.
- Pigmentation is most often located on the face, neck, trunk and proximal extremities. Mucosal surfaces, hair, nails, palms, and soles are not affected.
- Lesion size is typically less than 10 mm in diameter (range 0.5—2.5cm) [1,2].
- Macules are not scaly .
- A variant with raised velvety plaques is called idiopathic eruptive macular hyperpigmentation with papillomatosis .
- There is no preceding erythema.
- Pigmentation spontaneously regresses within a few months or years.
Idiopathic eruptive macular hyperpigmentation is not influenced by exposure to ultraviolet (UV) radiation .
Histology of idiopathic eruptive macular hyperpigmentation
Histopathological evaluation of a skin biopsy shows:
- Increased pigmentation of the epidermal basal cell layer
- Epidermal papillomatosis is observed rarely in the variant form
- Dermal melanophages and pigmentary incontinence in the absence of basal layer damage or dermal lichenoid inflammation is a contentious feature, believed by some to be an exclusion criterion 
- Sparse mast cells excludes cutaneous mastocytosis.
How is idiopathic eruptive macular hyperpigmentation diagnosed?
Diagnostic criteria were proposed by Sanz de Galeano :
- Eruption of brownish-black discrete, nonconfluent asymptomatic macules on neck, trunk and proximal extremities in children and adolescents.
- Basal-cell hyperpigmentation of the epidermis with dermal melanophages without any basal-cell damage or lichenoid infiltrate.
- Absence of preceding inflammatory lesions.
- No previous drug exposure.
- Normal mast cell count.
Suggested modifications have included clinical features of possible slightly raised plaques resembling acanthosis nigricans, and involvement of the face, and histology described as an epidermal hypermelanosis with or without papillomatosis in the absence of dermal inflammation .
A global consensus statement published in 2019 adds a further criterion that the pigmented macules have not appeared after a known episode such as a viral exanthem, pityriasis rosea, drug eruption, etc .
What is the differential diagnosis for idiopathic eruptive macular hyperpigmentation?
Idiopathic eruptive macular hyperpigmentation can be clinically misdiagnosed as one of the following conditions.
- Other forms of acquired dermal macular hyperpigmentation: lichen planus pigmentosus and erythema dyschromicum perstans. The distinguishing features are the age group affected, the size and distribution of the lesions, and the natural history .
- Fixed drug eruption; this recurs in association with a particular medication.
- Postinflammatory hyperpigmentation; this follows an injury or inflammatory skin disease.
- Maculopapular cutaneous mastocytosis; this is itchy and lesions may swell when rubbed (or they may blister in young children). Histology reveals excessive numbers of mast cells.
- Café-au-lait macules are light brown and do not spontaneously regress.
- Acanthosis nigricans has associated clinical features of insulin resistance or malignancy [1–3].
What is the treatment for idiopathic eruptive macular hyperpigmentation?
Treatment of idiopathic eruptive macular hyperpigmentation is not required because lesions are asymptomatic and resolve spontaneously within several months to years. Once cleared, there are no residual changes or scarring . Recurrence has not been reported.