Milia and Keratin Cysts

Milia are very common, benign, keratin-filled cysts. Primary milia are typically seen in infants but also may occur in children and adults. Secondary milia are observed in a number of blistering disorders and following dermabrasion. Milia en plaque and multiple eruptive milia are distinct entities.

The eMedicine Pediatrics article Milia may be of interest, as may the Medscape Dermatologic Surgery Resource Center.

Pathophysiology: Milia are tiny epidermoid cysts. The cysts may be derived from the pilosebaceous follicle. Primary milia arise on facial skin bearing vellus hair follicles.  Secondary milia result from damage to the pilosebaceous unit.

Frequency in the United States:
Primary milia in newborns are so common that they can be considered normal (occurring in approximately half of all infants). Multiple eruptive milia and milia en plaque are rare entities.

Race : No racial predilection is recognized.
Sex : Sexual prevalence is equal for primary and secondary milia. Eruptive milia and milia en plaque occur more frequently in women.
Age : Milia occur in persons of all ages but are typically found in infants.

Clinical History
Milia are asymptomatic. In children and adults, they usually arise around the eye. Eruptive milia, as the name suggests, have a rapid onset, often within a few weeks.

Physical
* Skin lesions
o Milia are superficial, uniform, pearly white to yellowish, domed lesions measuring 1-2 mm in diameter.
o In milia en plaque, multiple milia arise on an erythematous plaque.
* Skin distribution
o Primary milia, in term infants, occur on the face, especially the nose. They also may be found on the mucosa (Epstein pearls) and palate (Bohn nodules).
o Primary milia in older children and adults develop on the face, particularly around the eyes.
o Milia have been observed to occur in a transverse, linear distribution along the nasal groove in some children.
o Secondary milia are found anywhere on the body at the sites affected by the predisposing condition.
o Eruptive milia occur on the head, neck, and upper body.
o Milia en plaque manifests as distinct plaques on the head and neck. Plaques have been described in the postauricular area, unilaterally or bilaterally, the cheeks, the submandibular plaques, and on the pinna.

Causes
* Primary milia are believed to arise in sebaceous glands that are not fully developed, explaining the high prevalence in newborn infants.
* Secondary lesions arise following blistering or trauma due to disruption of the sweat ducts. Milia have been described in association with many disorders, including bullous pemphigoid, inherited and acquired epidermolysis bullosa, bullous lichen planus, porphyria cutanea tarda, and burns. Skin trauma from dermabrasion or radiotherapy can result in milia formation.
* Secondary milia have arisen from a bullous contact dermatitis and a photocontact allergy to sunscreen.

They have also arisen following treatment of cutaneous leishmaniasis and after topical nitrogen mustard ointment for plaque stage mycosis fungoides.
* Secondary milia have been described following potent topical corticosteroid use.
* Milia are a feature of a number of very rare genodermatoses (eg, Bazex-Dupré -Christol syndrome).  Both primary milia and multiple eruptive milia have been reported as familial disorders with autosomal dominant inheritance.
* The etiology of milia en plaque is unknown.

Medical Care
No topical or systemic medications are effective on primary and secondary milia. Single case reports have demonstrated the success of topical isotretinoin, oral etretinate and minocycline in treating patients with milia en plaque.

Surgical Care
Milia can be safely left alone, but if the patient requests treatment, then incision with a cutting-edge needle and manual expression of the contents are effective. This can be performed without local anesthetic. A paper clip has been successfully used to express the contents of the cyst. Milia en plaque has been treated effectively with electrodesiccation, carbon dioxide laser, dermabrasion, and cryosurgery.