Milia en plaque

Milia en plaque is a rare variant of primary milia, characterized by numerous aggregated milia appearing on within an inflamed plaque up to several centimeters in diameter ¹. Milia en plaque usually found on an eyelid, behind the ear, on a cheek or jaw. Milia en plaque has also been described as periorbital, on the nasal bridge, and truncal ¹. Milia are small, benign superficial keratin-filled cysts that result from the obstruction of a hair follicle or eccrine sweat ducts, measuring 1 to 4 mm in diameter ². Milia can be primary, appearing spontaneously, or secondary to trauma, skin disease, or medication ³. Milia en plaque affects children and adults, especially middle-aged women and 2 congenital cases ⁴, ⁵. Milia en plaque is sometimes associated with another skin disease including pseudoxanthoma elasticum, discoid lupus erythematosus ⁶, lichen planus, drugs such as cyclosporine, trauma and renal transplantation ¹.

Milia en plaque was first described by Balzer and Fouquet in 1903 and denominated by Hubler et al. in 1978 ¹. Since then, less than 40 cases have been reported in literature till date ⁷. Earlier reports described milia en plaque as a retroauricular dermatosis; however, later more case reports emerged with different sites of involvement like peri-orbital ⁸, pre-auricular ⁹, earlobes ¹⁰, sub-mandibular area ¹¹ and supraclavicular area ¹².

Milia en plaque is classified as primary milia deriving from the infundibulum of the vellus hair follicle and usually develops spontaneously in healthy skin with no clear cause ¹³. Milia are classified as primary when their onset is spontaneous and secondary when they appear following trauma (such as burn, dermabrasion, ablative laser etc.), inflammatory skin diseases (particularly those involving the basement membrane zone, such as sub-epidermal bullous diseases), or the use of topical medication (topical corticosteroids, 5-fluorouracil) or systemic drugs (cyclosporine and benoxaprofen) ¹⁴. Primary milia en plaque is a rare clinical variant characterized by numerous tiny milia within an erythematous base that arise spontaneously on a healthy skin in a predisposed individual without any apparent causative factor ¹. Evidences show that primary milia originate in the hair follicle infundibulum, whereas the secondary forms may develop in various adnexal structures like sweat ducts, sebaceous glands, and hair follicle ¹.

Despite being an asymptomatic benign lesion, milia en plaque can be a major cosmetic concern to the patient.

Dermoscopy is helpful in diagnosing early, inconspicuous milia (Figure 3). Histologically, milia en plaque is characterized by keratin-filled epidermal cysts and a mononuclear cell infiltrate ¹⁵.

There is no standard treatment for milia en plaque, but there are reports of milia en plaque being successfully treated by various medical as well as surgical treatments. Medical treatments of milia en plaque include topical tretinoin ¹, oral isotretinoin ¹⁶, etretinate ⁷, minocycline ¹⁰, photodynamic therapies ¹, producing variable response. Surgical modalities like simple extraction ¹⁷, electrodessication ¹⁸, dermabrasion ¹⁹ and CO2 laser evaporation ²⁰ had been tried with variable success. Spontaneous regression has also been reported ²¹.

Figure 1. Milia en plaque (milia en plaque lupus)

Footnote: Multiple yellowish cysts on an erythematous plaque and scattered open comedones in a malar distribution.

[Source ²² ]

Figure 2. Milia en plaque

Figure 3. Milia en plaque dermoscopy

Footnote: Dermoscopy found multiple milia cysts, follicular keratotic plugs, perifollicular whitish halos, pigmentation, and telangiectasia.

[Source ²² ]

Milia en plaque causes

Milia en plaque mostly arises in healthy individuals and most cases are idiopathic (unknown), though it has been found to be associated with pseudoxanthoma elasticum ²³, discoid lupus erythematosus ²⁴, mycosis fungoides ²⁵, lichen planus, systemic amyloidosis, trauma, and renal transplantation ²⁶, ²⁷, ²⁸. Certain medications, specifically cyclosporine, may be involved in the development of milia en plaque ²⁷. Additionally, a case of milia en plaque co-existing with cutis laxa was described in a patient who was taking penicillamine for more than 50 years ²⁹.

The pathogenesis of milia en plaque remains elusive. Boehm and colleagues ³⁰ proposed that damage to adnexal structures from underlying diseases results in the formation of milia. Milia en plaque after cryotherapy has been described, supporting the theory of trauma-induced milia ³¹. Kouba and colleagues ³² suggest that alteration in the infundibulum of a hair follicle, which causes impaired keratinization and outlet obstruction, plays a role in de novo milia en plaque. Ghosh and Sangal ⁵ postulate that intrauterine alteration in the infundibular portion and subsequent migration of the dysfunctional tissue contributes to the Blaschkoid pattern seen in congenital milia en plaque. Based on histopathological features, Terui and colleagues ³³ suggest that milia en plaque may represent a hamartoma, similar to a tumor of follicular infundibulum and trichoadenoma.

Milia en plaque signs and symptoms

Milia en plaque is an uncommon benign skin condition that presents as multiple, tiny, white papules situated within an erythematous plaque. Milia en plaque is typically asymptomatic. Milia en plaque preferentially involves the head and neck area, including nose, forehead, cheeks, scalp, periauricular, periorbital, submandibular and supraclavicular regions (Figures 1 and 2) ³⁴.

Lesions can be unilateral or bilateral ³⁵. A linear milia en plaque following Blaschko lines has also been described ³⁶.

Though most cases of milia en plaque have been described in adults, there were three case reports describing milia en plaque in children aged 6 years, 10 years, and 14 years ¹⁷, ¹⁸.

Milia en plaque diagnosis

Milia en plaque have a characteristic appearance. However, on occasion, a skin biopsy may be performed. Histopathologically, milia en plaque is characterized by keratin-filled epidermal cysts surrounded by a mononuclear cell infiltrate.

Milia en plaque should be distinguished from other types of cyst, comedones, xanthelasma and syringomas. Colloid milia are golden coloured bumps on cheeks and temples associated with excessive exposure to sunlight.

Milia en plaque should also be distinguished from milia-like cysts noted on dermoscopy in seborrhoeic keratoses, papillomatous moles and some basal cell carcinomas.

Milia en plaque treatment

Although milia en plaque is a benign condition, treatment is warranted if it causes a significant cosmetic disfigurement. Standard treatment for milia en plaque has not been established, but the condition can be treated with either medical or surgical modalities, including topical or oral retinoids, minocycline, photodynamic therapy, simple extraction, cryotherapy, ablative laser therapy, dermabrasion, electrodesiccation, or excision, with variable successes depending on the depth of the lesions ³⁷, ³⁸. Simple extraction and topical tretinoin are generally effective for superficial lesions. It should be noted, however, that recurrence is not uncommon ³⁹. Rarely, spontaneous resolution may occur ²¹.

References

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