Disorders of Keratinization

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Chapter 650 Disorders of Keratinization

Disorders of Cornification

Disorders of cornification (ichthyoses) are a primary group of inherited conditions characterized clinically by patterns of scaling and histopathologically by hyperkeratosis. They are usually distinguishable on the basis of inheritance patterns, clinical features, associated defects, and histopathologic changes (Table 650-1).

Harlequin Ichthyosis

Collodion Baby

Clinical Manifestations

Collodion babies are covered at birth by a thick, taut membrane resembling oiled parchment or collodion (Fig. 650-1), which is subsequently shed. Affected neonates have ectropion, flattening of the ears and nose, and fixation of the lips in an O-shaped configuration. Hair may be absent or may perforate the abnormal covering. The membrane cracks with initial respiratory efforts and, shortly after birth, begins to desquamate in large sheets. Complete shedding may take several weeks, and a new membrane may occasionally form in localized areas.

Neonatal morbidity and mortality may be due to cutaneous infection, aspiration pneumonia (squamous material), hypothermia, or hypernatremic dehydration from excessive transcutaneous fluid losses as a result of increased skin permeability. The outcome is uncertain, and accurate prognosis is impossible with respect to the subsequent development of ichthyosis.

Lamellar Ichthyosis and Congenital Ichthyosiform Erythroderma (Nonbullous Congenital Ichthyosiform Erythroderma)

Lamellar ichthyosis and congenital ichthyosiform erythroderma (nonbullous congenital ichthyosiform erythroderma) are the most common types of autosomal recessively inherited ichthyosis. Both forms are present soon or shortly after birth. Most infants with these forms of ichthyosis present with erythroderma and scaling; but among collodion babies, most turn out to have one of these ichthyosis variants.

Clinical Manifestations

After shedding of the collodion membrane, if present, lamellar ichthyosis evolves into large, quadrilateral, dark scales that are free at the edges and adherent at the center. Scaling is often pronounced and involves the entire body surface, including flexural surfaces (Fig. 650-2). The face is often markedly involved, including ectropion and small, crumpled ears. The palms and soles are generally hyperkeratotic. The hair may be sparse and fine, but the teeth and mucosal surfaces are normal. Unlike in congenital ichthyosiform erythroderma, there is little erythema.

In congenital ichthyosiform erythroderma, erythroderma tends to be persistent, and scales, although they are generalized, are finer and whiter than in lamellar ichthyosis (Fig. 650-3). Hyperkeratosis is particularly noticeable around the knees, elbows, and ankles. Palms and soles are uniformly hyperkeratotic. Patients have sparse hair, cicatricial alopecia, and nail dystrophy. Neither form includes blistering.

Ichthyosis Vulgaris

Clinical Manifestations

Ichthyosis vulgaris is the most common of the disorders of keratinization, with an incidence of 1/250 live births. Onset generally occurs in the 1st yr of life. In most cases, it is trivial, consisting only of slight roughening of the skin surface. Scaling is most prominent on the extensor aspects of the extremities, particularly the legs (Fig. 650-4). Flexural surfaces are spared, and the abdomen, neck, and face are relatively uninvolved. Keratosis pilaris, particularly on the upper arms and thighs, accentuated markings, and hyperkeratosis on the palms and soles, and atopy are relatively common. Scaling is most pronounced during the winter months and may abate completely during warm weather. There is no accompanying disorder of hair, teeth, mucosal surfaces, or other organ systems.