SECTION 4: ICHTHYOSES

ICHTHYOSES: INTRODUCTION

• A group of hereditary disorders characterized by an excess accumulation of cutaneous scale, varying from very mild and asymptomatic to life threatening.

• 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 along with a brief discussion of two syndromic ichthyoses and ichthyosis affecting the newborn.

• Acquired ichthyosis can be a manifestation of systemic disease, malignancy, drugs, endocrine disease, autoimmune disease, and HIV as well as other infections.

• Support groups such as Foundation for Ichthyosis and Related Skin Types (FIRST) exist.

CLASSIFICATION

Dominant ichthyosis vulgaris (DIV)

X-linked ichthyosis (XLI)

Lamellar ichthyosis (LI)

Epidermolytic hyperkeratosis (EH)

This simplified classification is presented here for clinical-diagnostic and didactical reasons. A scientific classification based on molecular genetics is found in P. Fleckman and J. DiGiovanna: The Ichthyoses in Goldsmith, Katz, Gilchrest, Paller, Leffell, Wolff (eds.) Fitzpatrick's Dermatology in General Medicine, 8th edition, New York, McGraw-Hill, 2012, pp. 507–537.

DOMINANT ICHTHYOSIS VULGARIS (DIV) ICD-10: Q 80.0

• Characterized by usually mild generalized xerosis with scaling, most pronounced on lower legs; in severe cases large, tessellated scales.

• Hyperlinear palms and soles.

• Perifollicular hyperkeratosis (keratosis pilaris) usually on arms and legs.

• Frequently associated with atopy.

EPIDEMIOLOGY

AGE OF ONSET 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. When hyperkeratosis is severe, many patients have a cosmetic concern.

SKIN LESIONS Xerosis (dry skin) with fine, powdery scaling but also larger, firmly adherent tacked-down scales in a fish-scale pattern (Figs. 4-1 and 4-2). Diffuse general involvement, accentuated on the shins, arms, and back, buttocks, and lateral thighs; axillae and the antecubital and popliteal fossae spared (Figs. 4-2 and 4-3). The face is usually spared but the cheeks and forehead may be involved. Keratosis pilaris is perifollicular hyperkeratosis with little, spiny hyperkeratotic follicular papules of normal skin color either grouped or disseminated, mostly on the extensor surfaces of the extremities (Fig. 4-4); in childhood, also on cheeks. The hands and feet usually spared, but palmoplantar markings are more accentuated (hyperlinear).