Colloid Milium

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]

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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.

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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.

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Prognosis

Colloid milium lesions remain static and do not resolve. Lesions reach their peak within 3 years, after which very few new papules occur.

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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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History

Papules develop gradually over the facial area and light-exposed sites. Patients with colloid milium are usually asymptomatic, but they may have transient itching in affected areas.

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Physical Examination

The physical findings in colloid milium are usually limited to the skin.

Skin lesions of colloid milium

Amber, waxy, partially translucent, firm papules occur in crops, ranging from 1-5 mm in diameter. Gelatinous material can be expressed. In the nodular form, larger nodules (5-10 mm) or plaques develop. The underlying skin may be thickened, furrowed, and hyperpigmented. In the pigmented form, the papules are gray-black and confluent or clustered.

Skin distribution of colloid milium lesions

The lesions occur on light-exposed skin, with the cheeks, periorbital area, nose, ears, and neck most frequently involved; however, lesions may also occur on the backs of the hands and forearms. Nodules arising on one side of the face and the ipsilateral forearm have been described in a taxi cab driver. Upper eyelid margin involvement alone has been reported.^[14] One case report describes nodular colloid milium affecting the conjunctiva and anterior orbit.^[15] Juvenile colloid milium may be associated with ligneous conjunctivitis or ligneous periodontitis.^[16] Rarely, lesions occur in the oral cavity.^[17]

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Causes

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]

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Procedures

Skin biopsy in colloid milium

Light microscopy is necessary. Electron microscopy may be necessary to distinguish between colloid and amyloid because these 2 entities look similar under light microscopy.

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Histologic Findings

Typically, fissured eosinophilic colloid masses are seen in the dermis.^[18]

In the classic adult form of colloid milium, the colloid is located in the upper and mid dermis and in defined islands, with a very superficial, subepidermal layer of the papillary dermis usually being spared (grenz zone). The colloid has a homogeneous eosinophilic appearance with some fissuring. Fibroblasts may be aligned along the edges of these fissures. Solar elastosis is marked and closely approximated to the colloid. Hair follicles and sebaceous glands are well preserved.

In the nodular form of colloid milium, the vast majority of the dermis is filled with glassy eosinophilic colloid.

In the pigmented form of colloid milium, deposits are similar to those of the classic adult form of colloid milium, except that they show a light-golden pigmentation similar to ochronosis.

In the juvenile form of colloid milium, the grenz zone is usually absent, with the islands of amorphous colloid lying close to the basal layer of the epidermis. These islands show some clefting with intervening spindle or stellate fibroblasts. Solar elastosis is absent. In the nodular form of colloid milium, the vast majority of the dermis is filled with colloid.

Because colloid cannot be distinguished from amyloid under light microscopy alone and because colloid, like amyloid, stains positively for periodic acid-Schiff stain, it can be difficult to distinguish it from amyloid. However, colloid is usually negative for the amyloid stain methyl (crystal) violet. Colloid may also sometimes yield weakly positive results and may show green birefringence with Congo red stain. Amyloid in the skin frequently immunostains positively for cytokeratin or immunoglobulin light chain, which colloid should not. However, if these special stains and immunostains prove inconclusive, electron microscopy may be necessary.^{[6, 19]}

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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.

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Approach Considerations

For colloid milium, no treatment is available that is entirely satisfactory.

Dermabrasion,^[20] cryotherapy, and diathermy have been tried with limited success. Advice about sunscreen use may also be helpful. Systemic ascorbic acid and exfoliating agents have also been tried with variable results. The Er:YAG laser may be more successful for colloid milium than dermabrasion.^[21] A nonablative 1550-nm erbium-glass fractional laser^[22] and a fractionated carbon dioxide laser^[23] have also been used to treat colloid milium successfully. One case report describes successful treatment with photodynamic therapy using methyl-aminolevulinate (MAL) cream as a photosensitizer.^[24]

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