Background
Colloid milium is a rare condition characterized by (1) the presence of multiple, dome-shaped, amber- or flesh-colored papules developing on light-exposed skin and (2) the observance of dermal colloid under light microscopy. The 4 variants are (1) an adult-onset type, (2) a nodular form (nodular colloid degeneration), [1] (3) a juvenile form, [2, 3] and (4) a pigmented form, thought to be due to excess hydroquinone use for skin bleaching. [4]
Pathophysiology
Colloid milium is a degenerative condition linked to excessive sun exposure and possibly exposure to petroleum products and hydroquinone. The origin of the colloid deposition in the dermis is not certain, but it is thought to be due to degeneration of elastic fibers [5, 6] in the adult form and due to degeneration of UV-transformed keratinocytes in the juvenile form. Juvenile colloid milium is inherited.
Etiology
The classic adult and nodular forms of colloid milium are believed to be due to excessive sun exposure, which appears to cause degeneration of elastin. Evidence to support this comes from the exposed site distribution and the tendency for colloid milium to occur in individuals with fair complexions and outdoor occupations. [7, 8]
The juvenile form of colloid milium is inherited, perhaps suggesting an inherited susceptibility to UV light. Autosomal recessive inheritance [9] and a familial case affecting father and son [10] have been reported.
An outbreak of colloid milium occurred in oil refinery workers in the tropics. [11] A mechanic with occupational exposure to lubricating oils developed colloid milium over the backs of the hands. [12] This may represent an interplay between light and petroleum constituents. Phenols have been suggested as causative agents.
Prolonged use of hydroquinones has resulted in the development of the pigmented form of colloid milium, sometimes in association with ochronosis. [13]
Epidemiology
Frequency
Colloid milium is rare, but more than 100 case reports are present in the world literature. No known figures exist on prevalence.
Race
Colloid milium is more common in fair-skinned individuals.
Sex
The adult form of colloid milium is more common in males.
Age
The rare juvenile form of colloid milium occurs before puberty. Adult colloid milium is more common in elderly patients.
Prognosis
Colloid milium lesions remain static and do not resolve. Lesions reach their peak within 3 years, after which very few new papules occur.
Patient Education
Genetic counseling is advisable for the rare juvenile form of colloid milium. Additionally, sun avoidance seems sensible for all forms of colloid milium, but no evidence suggests that this intervention is beneficial.
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Hematoxylin and eosin–stained section of skin (X40) showing a central focus of amorphous, eosinophilic, homogenous colloid with surrounding fissuring.
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Elastic van Gieson stain of the same area showing strong (black) staining of the colloid for elastin.
