What's in this article?
Ichthyosis (plural ichthyoses) is a heterogeneous family of at least 28, generalized, mostly genetic skin disorders.
All types of ichthyosis have dry, thickened, scaly or flaky skin. In many types there is cracked skin, which is said to resemble the scales on a fish; the word ichthyosis comes from the Ancient Greek ἰχθύς (ichthys), meaning “fish.”
The severity of symptoms can vary enormously, from the mildest, most common, type such as ichthyosis vulgaris which may be mistaken for normal dry skin up to life-threatening conditions such as harlequin type ichthyosis. Ichthyosis vulgaris accounts for more than 95% of cases.
Who gets ichthyosis?
Inherited forms of ichthyosis
Inherited forms of ichthyosis may be congenital or have delayed onset.
- Ichthyosis vulgaris (1:250—1000) has autosomal dominant inheritance, meaning an abnormal gene is inherited from a parent. Penetrance is 90%. Onset is delayed until at least 3 months of age.
- Recessive X-linked ichthyosis (1:2000—6000) mainly affects males, who have a single X chromosome with the abnormal gene. Females are protected by usually having a normal second X chromosome. Onset may be congenital or delayed by up to 6 months.
- In autosomal recessive congenital ichthyosis (1:3–500,000) one abnormal gene is inherited from each parent.
- Keratinopathic ichthyoses (1:200,000) have recessive and dominant forms and present at birth with a collodion membrane.
Ichthyosis can also be due to new spontaneous mutation.
Acquired ichthyosis
Acquired ichthyosis appears in adult life. People with ichthyosis may have systemic disease, such as:
- Underactive thyroid
- Sarcoidosis
- Hodgkin lymphoma
- Cancer (ichthyosis may be a cutaneous marker of internal malignancy)
- HIV infection
Ichthyosis may be provoked by certain medications:
- Nicotinic acid
- Kava
- Targeted cancer therapy (eg vemurafenib, EGFR and protein kinase inhibitors)
- Hydroxyurea
What Are the Different Types of Ichthyosis?
There are many different types of inherited ichthyosis. Most types involve only the skin, and some regions of the skin may be more severely affected than others. Other types involve internal organs as well as the skin, and are referred to as syndromic types of ichthyosis. Although there is an increase in the tendency to categorize inherited ichthyosis by the gene that causes it, the clinical appearance usually falls into one of five categories
Different Types of Ichthyosis
- Ichthyosis vulgaris. Characterized by mild skin scaling and dryness. Ichthyosis vulgaris and another form, recessive X-linked ichthyosis, are relatively common and appear similar.
- Epidermolytic ichthyosis (previously called epidermolytic hyperkeratisis).Characterized by thick, often spiny dark scales and skin that may blister easily following trauma.
- Lamellar ichthyosis. Characterized by large, platelike scales and thickening of the skin.
- Congenital ichthyosiform erythroderma. Characterized by red skin and fine scales.
- Localized ichthyosis. Characterized by thick or scaly skin that is localized to particular regions such as the palms of the hands and soles of the feet
Other types of inherited ichthyosis
Other inherited forms of ichthyosis are very rare and include:
- X-linked ichthyosis – this only affects males and includes general scaling, particularly over the limbs, neck and buttocks
- congenital ichthyosiform erythroderma
Ichthyosis may develop if a baby is born with a shiny yellow membrane (collodion membrane) that sheds within the first week of life. Once the membrane has shed, one of the following types of ichthyosis can develop:
- non-bullous ichthyosiform erythroderma – inflamed, scaly skin affecting the entire skin surface
- bullous ichthyosiform erythroderma – inflamed, scaly skin with fluid-filled blisters that may become infected and produce a foul-smelling skin odour
- lamellar ichthyosis – where the skin is not as red, but the scales are larger and tighter to the skin
In severe cases of congenital ichthyosiform erythroderma, a child may also have drooping lower eyelids (ectropion), mild hair loss and tight skin on the fingers.
- harlequin ichthyosis – this is extremely rare, but the scaling is severe and requires intensive care at birth
- syndromes that include ichthyosis – such as Netherton’s syndrome or Sjogren-Larsson syndrome
Congenital ichthyosiform erythroderma
Ichthyosis may develop if a baby is born with a shiny yellow membrane (collodion membrane) that sheds within the first week of life. Once the membrane has shed, one of the following types of ichthyosis can develop:
- non-bullous ichthyosiform erythroderma – inflamed, scaly skin affecting the entire skin surface
- bullous ichthyosiform erythroderma – inflamed, scaly skin with fluid-filled blisters that may become infected and produce a foul-smelling skin odour
- lamellar ichthyosis – where the skin is not as red, but the scales are larger and tighter to the skin
In severe cases of congenital ichthyosiform erythroderma, a child may also have drooping lower eyelids (ectropion), mild hair loss and tight skin on the fingers.
Congenital ichthyosiform erythroderma
There are two types of ichthyosis in this category. They generally declare themselves at birth with the appearance of a so-called collodion membrane on the newborn baby. This is a shiny yellow film stretched across the skin like a sausage skin. It dries out and gradually sheds within the first week of life. The “collodion baby” is nursed in a humidified incubator until the skin settles down. The majority of collodion babies will develop congenital ichthyosiform erythroderma. However, a small number of these babies will have normal skin once the membrane is shed and, therefore, it is not possible to accurately predict the outcome in the early stages.
Most collodion babies develop non-bullous ichthyosiform erythroderma, which literally means inflamed, scaly skin, without blisters. It affects 1 in every 300,000 births and so is quite rare. Once the collodion membrane has shed, the skin remains red and has fine, white scales affecting the entire skin surface. In severely affected children the eyelids may be pulled outwards and there may be some mild scalp hair loss and tightness of the fingers. Because the skin is inflamed it will feel hot, even if the child is cold. Most children with this condition do not sweat normally and may overheat in hot weather, when exercising or with a fever. The palms and soles are sometimes thickened and scaly. Otherwise a child’s health is normal. They may suffer cosmetically and this is especially important when a child starts school, or in the teenage years.
The less common form of congenital ichthyosiform erythroderma is lamellar ichthyosis. This is different in that the skin is less red but the scaling is larger, perhaps darker and more adherent, or stuck down.
These two conditions are passed on by parents with normal skin who both carry the abnormal gene (autosomal recessive) and the risk of a further child being affected is 1 in 4. They can be diagnosed on a skin biopsy from the foetus taken halfway (between 18 – 20 weeks) through a pregnancy, if the parents want to know; however, there is no way of preventing them before conception, as the abnormal gene has not yet been identified.
