Section 4

Rare
Not so common
Common
Low morbidity
Considerable morbidity
Serious

• A group of hereditary disorders characterized by an excess accumulation of cutaneous scale, varying from very mild and asymptomatic to lifethreatening.
• A relatively large number of types of hereditary ichthyoses exist; most are extremely rare and often part of multiorgan syndromes. The four most common and important types are discussed here plus a brief discussion of two types affecting newborns.
• Acquired ichthyosis can be a manifestation of systemic disease, malignancy, drugs, endocrine disease, autoimmune disease, and HIV and other infections.
• Support groups such as Foundation for Ichthyosis and Related Skin Types (FIRST) exist.

For an in-depth discussion of ichthyoses, see P Fleckman, JJ DiGiovanna, in K Wolff et al (eds): Fitzpatrick's Dermatology in General Medicine, 7th ed. New York, McGraw-Hill, pp 401–424, 2008.

### Classification

• Dominant ichthyosis vulgaris (DIV)
• Lamellar ichthyosis (LI)
• Epidermolytic hyperkeratosis (EH)

### Etiology and Pathogenesis

Individual keratin genes may not be expressed or may result in the formation of abnormal keratins. In DIV and XLI, formation of thickened stratum corneum is caused by increased adhesiveness of the stratum corneum cells and/or failure of normal cell separation. Abnormal stratum corneum formation results in variable increases in transepidermal water loss. The etiology of the most common ichthyosis, DIV, is unknown, but there are mutations in the gene encoding profilaggrin; in XLI, there is a steroid sulfatase deficiency. LI shows increased germinative cell hyperplasia and increased transit rate through the epidermis, and there is a transglutaminase deficiency. In EH, there are mutations in the genes encoding keratins 1 or 10; here the disturbance of epidermal differentiation and the expression of abnormal keratin genes result in vacuolization of the upper epidermal layers, blistering, and hyperkeratosis.

### Clinical Manifestation

All four types of ichthyosis tend to be worse during the dry, cold winter months and improve during the hot, humid summer. Patients living in tropical climates may remain symptom-free but may experience appearance or worsening of symptoms on moving to a temperate climate.

ICD-9 : 757.1 • ICD-10 : Q 80.0

• Characterized by usually mild generalized xerosis with scaling, most pronounced on lower legs; in severe cases large, tessellated scales occur.
• Hyperlinear palms and soles.
• Perifollicular hyperkeratosis (keratosis pilaris) usually on arms and legs.
• Frequently associated with atopy.

### Epidemiology

3 to 12 months.

#### Sex

Equal incidence in males and females. Autosomal dominant inheritance.

#### Incidence

Common (1 in 250).

### Pathogenesis

Etiology unknown. There is reduced or absent filaggrin. Epidermis proliferates normally, but keratin is retained with a resultant thickened stratum corneum.

### Clinical Manifestation

Very commonly associated with atopy. Xerosis and pruritus worse in ...

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