Porokeratosis Of Mibelli

A rare skin disease that is characterized by the presence of brownish single or multiple annular plaques of varying size, that are sometimes confluent, with a distinctive sharply-defined keratotic border.

Epidemiology

Porokeratosis of Mibelli (PM) prevalence is unknown. It is more prevalent in males than females with a ratio of 2-3:1.

Clinical description

Disease onset usually occurs in children, adolescents or young adults (sometimes immunosuppressed). It presents with brownish dry hyperkeratotic plaques of varying size that may coalesce. The lesions have a sharply-defined keratotic border and are usually asymptomatic, but rarely pruritic. They most commonly occur on the limbs (hands and feet) but other areas such as the trunk, palms and soles and genitalia can also be affected. Facial and mucosal lesions are rare. In around 7% of cases, PM lesions undergo malignant transformation, mostly toward squamous cell carcinoma, or less commonly, basal cell carcinoma.

Etiology

The exact etiology is unknown but the lesions are thought to originate from the localized expansion of a clone of abnormal keratinocytes. Contributing factors include immunosuppression, exposure to ultraviolet radiation and drugs, as well as genetic factors (mutations in mevalonate kinase gene).

Diagnostic methods

Diagnosis is based on physical examination and a cutaneous biopsy showing the distinctive cornoid lamella, i.e. a narrow, vertical stack of parakeratotic corneocytes within the horny layer seated on a depression of the underlying epidermis.

Differential diagnosis

The main differential diagnoses are actinic keratosis, elastosis perforans serpiginosa, annular lichen planus, circumscribed palmoplantar hypokeratosis, psoriasis, focal palmoplantar keratoderma and Bowen's disease.

Genetic counseling

Autosomal dominant inheritance has been reported, although PM is often sporadic.

Management and treatment

PM lesions can be treated with surgical excision. Alternative, albeit less efficient, options include topical 5-fluorouracil (5-FU), imiquimod, cryotherapy, dermabrasion, carbon dioxide laser ablation and photodynamic therapy. However the lesions often recur after treatment. Regular follow-up is recommended to monitor the development of any possible malignancies, and sun exposure should be limited in order to decrease their risk.

Prognosis

PM is a chronically progressive disease and can have a negative impact on a patient's quality of life due to the presence of lesions. Rarely (in around 7% of cases), long-standing lesions may transform into squamous cell carcinoma, which has exceptionally proven fatal.