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any in a group of skin disorders characterized by increased or aberrant keratinization, resulting in dryness, roughness, and scaliness of the skin. Many different metaphors such as alligator, collodion, crocodile, fish, and porcupine skin have been used to describe the various types and stages of ichthyosis. Most ichthyoses are genetically determined, but some may be acquired and develop in association with systemic diseases or may be a prominent feature in certain genetic syndromes. The term is commonly used alone to refer to ichthyosis vulgaris. (See Atlas 2, Part L.) adj., adj ichthyot´ic.
ichthyosis conge´nita (congenital ichthyosis) lamellar exfoliation of newborn.
harlequin ichthyosis the ichthyosis affecting a harlequin fetus.
ichthyosis hys´trix a rare form of epidermolytic hyperkeratosis marked by generalized, dark brown, linear, wartlike ridges somewhat like porcupine skin.
lamellar ichthyosis a congenital, chronic form of ichthyosis present at birth, inherited as an autosomal recessive trait, in which the affected infant is born encased in a collodionlike membrane (see collodion baby) that is soon shed, the skin then becoming covered with large, coarse scales with involvement of all of the flexures as well as the palms and soles. Universal erythroderma and pruritus are characteristic, and ectropion of variable degree is usually present. Formerly called congenital ichthyosiform erythroderma (nonbullous type). (See Atlas 2, Part K.)
lamellar ichthyosis of newborn lamellar exfoliation of newborn.
ichthyosis linea´ris circumflex´a a congenital autosomal recessive disorder present at birth, characterized by the presence of generalized redness and scaling of the skin associated with migratory lesions and hyperhidrosis of the palms and soles.
ichthyosis vulga´ris the most common form of ichthyosis, inherited as an autosomal dominant trait, having an onset sometime after the first year of life, especially near puberty. There is prominent fine scaling, principally on the extensor surfaces of the extremities and back (the flexures are spared and there is little scaling of the abdomen and face), together with accentuated markings and creases on the palms and soles; atopy is often present.
X-linked ichthyosis a chronic form of ichthyosis affecting only males, transmitted as an X-linked recessive trait, that may be present at birth or appear in early infancy. It is characterized by the presence of prominent, very adherent scales, often brown, especially on the neck, extremities, trunk, and buttocks.
a fetal form of ichthyosis thought to be distinct from lamellar ichthyosis, with plaques having a diamondlike shape resembling the suit of a harlequin character; the keratinocytes contain increased amounts of tonofibrils, which are fibrillar structural proteins; autosomal recessive inheritance.