Last Updated: 2023-10-12
Author(s): Lindemann H.
ICD11: EC20.00, Q80.0
Lorry, 1777; Willian,1808; Wells and Kerr, 1966
Fish scale disease, ichthyosis simplex, autosomal-semidominant ichthyosis vulgaris (ADI)
It is an autosomal (semi-)dominantly inherited keratinisation disorder with varying clinical expressivity. Mutations in the filaggrin gene (FLG gene) lead to firmly adherent scales on sebostatic skin. Patients often suffer from minor subjective complaints, such as mild itching.
There is a correlation with diseases of the atopic type.
Mild and severe forms of progression can be distinguished depending on the clinic.
Mild forms of the disease (about 1/3 of those affected) have a mutation in the filaggrin gene
Severe courses (about 2/3 of those affected) have two mutations in the filaggrin gene
Over 40 mutations have been detected in the filaggrin gene. Predominantly, these are loss-of-function mutations that cause reduced or absent expression of filaggrin or profilaggrin.
In the terminal differentiation of keratinocytes, profilaggrin is cleaved into filaggrin peptides. Filaggrin functions as a structural protein and connects keratinocytes to each other via disulphide bridges. Filaggrin is finally converted into water-storing amino acids and thus moisturises the skin. In ichthyosis vulgaris, the disruption of the filaggrin function leads to a disturbed skin barrier. This leads to a loss of moisture, inflammation and unprotected exposure to potential allergens. This leads to the increased development of atopic diseases.
Ichthyosis vulgaris is usually not visible at birth. The skin changes often appear at 4-6 months of age. There are usually fine light grey, firmly adherent scales on the extremities. Often, groins and flexor sides remain free of scales due to the higher moisture content. There may be mild hyperkeratosis, as well as hyperlinearity on the hands and feet.
The skin changes are extremely variable. In mild courses, skin changes are hardly noticeable. In contrast, severe courses show large scales, typically with a central attachment and loose fringe. There may be scaling on the trunk, scalp or face and marked hyperkeratosis of the hands and feet with painful rhagades. Subjective symptoms are rare. There may be mild itching.
The diagnosis is usually made via the clinic. Human genetic analyses and histological examinations can confirm the diagnosis. One difficulty is the high correlation of ichthyosis vulgaris and atopic dermatitis. Due to the classic involvement of the flexor sides in the context of atopic dermatitis, ichthyosis vulgaris may be overlooked as a causative component. Here, the flexor sides would typically not be affected.
The disease manifests itself especially on the extensor sides of the extremities.
Mild orthokeratotic hyperkeratosis. Often a reduced or absent granular layer can be detected. Hyperkeratosis of the hair follicles and acrosyringia are often found. The epidermis may appear acanthotic or atrophic. Perivascular lymphocytic infiltrates may be found sporadically. The keratohyaline granules may be absent or structurally disturbed. Immunohistochemistry may demonstrate an absent or reduced filaggrin content.
With increasing age, ichthyosis vulgaris may improve. There are seasonal variations. Classically, there is an improvement in summer.
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