Ichthyoses

Published on 19/03/2015 by admin

Filed under Dermatology

Last modified 19/03/2015

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Ichthyoses

John Newsham, Nina R. Farquharson and Timothy H. Clayton

Evidence Levels:  A Double-blind study  B Clinical trial ≥ 20 subjects  C Clinical trial < 20 subjects  D Series ≥ 5 subjects  E Anecdotal case reports

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The ichthyoses represent a group of disorders of keratinization characterized by scaly skin. They may be inherited or acquired. Severity and extent vary widely from mild ichthyosis vulgaris (IV) to life-threatening harlequin ichthyosis. Recent developments have led to the identification of several causative genes and provided targets for future therapies.

Management strategy

The key to management, where possible, is to establish an exact diagnosis. This provides a platform to plan therapy, discuss prognosis, and consider genetic counseling. It is important to identify the age of onset, the presence or absence of collodion membrane, blistering or erythroderma in the neonatal period, and the type, color, and distribution of scale. Family members should be examined. The Ichthyosis Support Group (ISG) provides a support network for families with resources and information sheets (www.ichthyosis.org.uk).

Causative genes for a number of the inherited ichthyoses have recently been identified. IV is the most common disorder of cornification, with an incidence of 1 : 250. It is not usually present at birth. Clinical features include dry skin with associated fine white powdery scale on extensor surfaces, palmar hyperlinearity, and keratosis pilaris. Mutations in the filament aggregating protein (filaggrin) gene (FLG) have recently been identified as the cause of IV. Loss-of-function mutations in FLG have also been strongly associated with atopic dermatitis. Identifying the genes responsible for the various types of ichthyosis may provide targeted treatments with the potential to alleviate or even prevent disease in susceptible individuals.

Patients with ichthyosis have reduced epidermal barrier function, increased trans-epidermal water loss, reduced pliability of the stratum corneum, and hyperkeratosis. Topical treatment involves hydration, lubrication, and keratolysis. There have been no randomized controlled studies exploring the role of emollients in the management of ichthyosis. However, emollients are widely used as a first-line treatment. In mild to moderate cases emollients alone are often sufficient. Increasing the environmental humidity has also been shown to be beneficial. Emollient baths aid in softening the stratum corneum and facilitate mechanical debridement of thickened hyperkeratosis.

Keratolytics such as salicylic acid, urea, lactic acid, and propylene glycol reduce the adhesion of keratinocytes. However, because of the impaired barrier function, care should be taken to prevent salicylate toxicity. We do not advocate the use of topical salicylic acid in children due to the increased surface area to volume ratio. Cutaneous infection occurs as a result of impaired barrier function and consideration should be given to prophylactic measures, such as antiseptic soaps or baths. Skin infection may require topical and systemic antibacterials, particularly in epidermolytic hyperkeratosis (EHK), which often requires long-term antibiotic therapy.

Topical retinoids (e.g., tretinoin) may be beneficial. They reduce the cohesiveness of epithelial cells, stimulate mitosis and turnover, and suppress keratin synthesis.

The severe ichthyoses usually respond to systemic retinoid therapy. Acitretin (1 mg/kg/day) and isotretinoin (1–2 mg/kg/day) have been shown to reduce scaling and discomfort, and improve heat tolerance and sweating. However, recurrence of ichthyotic skin occurs on discontinuing treatment, thereby necessitating long-term use. Long-term treatment involves a higher risk of chronic skeletal toxicity, such as calcification of tendons and ligaments, hyperostoses, and osteoporosis, which requires regular monitoring. Alitretinoin may provide a safer alternative to acitretin and further studies are necessary to assess its efficacy.

Retinoic acid metabolism-blocking agents have been shown to inhibit the cytochrome P450-dependent 4-hydroxylation of retinoic acid, resulting in increased tissue levels of retinoic acid and a reduction in epidermal proliferation and scaling. Drugs such as liarozole have been studied but no recent data is available and there are no on-going trials with this particular treatment.

Acquired ichthyoses are associated with a number of systemic disorders, including HIV, malignancy, sarcoidosis, leprosy, thyroid disease, hyperparathyroidism, nutritional disorders, chronic renal failure, and autoimmune diseases. They will often improve with treatment of the underlying condition. There have been few publications in recent years relating to acquired ichthyosis.

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