Adult Colloid Milium

For 6 years, slightly pruritic “bumps” had been present on the ears of a 52-year-old man. He had worked at an oil refinery for 30 years and had an extensive history of unprotected sun exposure.

Examination revealed multiple firm, translucent, skin-colored papules on the antitragus and lobes of his ears bilaterally. The papules ranged from 0.5 to 5 mm in size, and with slight pressure a mucoid substance could be expressed from the papules. He had similar lesions on his nose and the dorsa of both hands. The surrounding skin had significant photodamage. A diagnosis of colloid milium was made.

Colloid milium is a rare cutaneous deposition disease characterized by small, translucent papules resulting from colloid deposition in the papillary dermis.¹ There are three clinical types: adult colloid milium (ACM), juvenile colloid milium, and nodular colloid degeneration. Although the exact prevalence is unknown, ACM is the most common form.¹ It is seen most frequently in middle-aged fair-skinned men with a history of prolonged sun exposure and chronic exposure to petroleum products.^2,3

Lesions are located primarily in sun-exposed areas, such as the nose, ears, neck, periorbital region, and dorsa of the hands.⁴ The lesions are usually asymptomatic; however, patients may report transient pruritus and bleeding with minor trauma.²

The pathogenesis of ACM is poorly understood. Chronic ultraviolet (UV) light exposure is thought to play a major role in the development of ACM. The prevailing opinion on the origin of colloid describes the material as derived from the actinic degeneration of elastic fibers.² In addition to sunlight as a risk factor, many patients—and in the experience of one of the authors (Dr Wilson) most—report occupational exposure to phenols and/or petroleum derivatives.^2,5 These substances are thought to enhance the effect of UV light on the skin.⁵

Juvenile colloid milium is an extremely rare familial form with onset before puberty. While the mode of inheritance is unclear, this disease may represent a genetic predisposition to sun-induced keratinocyte damage.¹ The lesions are clinically indistinguishable from ACM, and they may develop following severe sunburn.

Nodular colloid degeneration is characterized by isolated or multiple nodules and plaques up to 5.0 cm in size.⁵ These lesions usually involve the face, although they may also be found on the neck, trunk, and scalp.² This form of colloid milium may be unrelated to UV light exposure, since nodules have been reported in unexposed areas.¹

Colloid milium is typically a clinical diagnosis. The differential diagnosis of ACM is extensive and includes amyloidosis (systemic or primary cutaneous), syringomas, sarcoidosis, steatocystoma multiplex, lipoid proteinosis, molluscum contagiosum, and sebaceous hyperplasia.² If the clinical picture is unclear, a biopsy may be performed. Histologic examination of ACM reveals homogenous, fissured, eosinophilic colloid material in the papillary dermis. ACM may be confused with amyloidosis histologically, yet the diseases may be distinguished by electron microscopy if necessary.²

The treatment of ACM is limited. Chemical exfoliative agents, cryotherapy, and dermabrasion have been used with marginal success.^3,6 Some have explained these limited outcomes by the fact that colloid cysts of ACM may be too deep to be removed by chemical peels.^2,6 More recently, laser treatment has been used with good response.^2,3 In addition, aggressive photoprotection should be recommended.