Ichthyoses

ICD-11

ED50.Z

Epidemiology

Ichthyosis vulgaris: prevalence 1:250- 1:1000 newborns.

X-linked recessive ichthyosis: 1:2000-1:6000 Males.

Autosomal recessive congenital ichthyosis (ARCI): 1:100000.

Acquired ichthyosis: unknown.

Syndromic ichthyosis: unknown.

Definition

Group of hereditary disorders of keratinisation with different patterns of inheritance and genetic defects.
Group of acquired disorders of keratinisation of different origin.

Aetiology & Pathogenesis

Ichthyosis vulgaris: autosomal dominant. Loss-of-function mutations in the gene coding profilaggrin (FLG).
X-linked recessive ichthyosis: hereditary deficiency of the steroid sulfatase (STS) gene deletions.
Autosomal recessive congenital ichthyosis (ARCI): defects in keratin genes, transglutaminase, or other structural proteins.
Acquired ichthyosis: associated with HIV infection, certain drugs, such as, statins, paraneoplastic diseases (see chapter 3.2.11), cutaneous T-cell lymphomas, metabolic disorders.
Syndromic ichthyosis.

Signs & Symptoms

Mild to severe scaling and hyperkeratosis.

Ichthyosis vulgaris: starts in 1st year of life, dry rough scaly skin, symmetrical on the trunk and extremities, especially on flexural areas, hyperlinearity of palms and soles. 50% of cases associated with atopic dermatitis.
X-linked recessive ichthyosis: similar to ichthyosis vulgaris, but flexures are involved, undescended testes in 30%. Large, dark-brown scales, lesions spread to the whole body.
Autosomal recessive congenital ichthyosis (ARCI): generalised ichthyosis, present at birth often associated with erythroderma. Occasionally ectropion of eyelids.

Collodion baby: newborn with thick, stiff fissured sheets of stratum corneum; many causes. Initial manifestation of a ARCI.

Localisation

Extremities, especially on flexural areas, groin, palms and soles, lower legs.
All body surface in the extensive forms.

Classification

Non syndromic: only affecting the skin (ichthyosis vulgaris, ARCI, epidermolytic ichthyosis, acquired ichthyosis and others).
Syndromic: involvement of other organ systems in addition to the skin (Chanarin-Dorfman syndrome, Comèl-Netherton syndrome, keratitis. Ichthyosis and deafness syndrome, Refsum’s disease, Sjögren-Larsson syndrome, trichothiodystrophy, and others).

Laboratory & other workups

Complete blood count, electrolytes, hepatic panel, immunoglobulin levels (including IgE). Peripheral blood smear to evaluate for vacuoles in leukocytes. Hearing screening. Ophthamologic examination. X-rays to evaluate epiphyses. Skin biopsy and genetic test. Transepidermal water loss.

Dermatopathology

Main features: Mild orthokeratotic hyperkeratosis, diminished or thickened granular layer. Immunohistochemistry demonstrates diminished or absent filaggrin. Specific subtypes exist by histology.

Course

Severity and symptoms (itch) depend on the season and the climate, improving in the summer and with high humidity. Ichthyosis vulgaris is usually progressive during childhood, and improves with age.

Complications

Bacterial super-infections. Psychosocial problems. Reduced sweating, complicated thermo regulation, hair loss.

Diagnosis

Clinical
Histology
Blood and molecular tests

Differential diagnosis

Asteatotic skin, exsiccation eczema, erythroderma in lymphomas, erythrodermic psoriasis, erythrodermic atopic dermatitis.

Prevention & Therapy

Prenatal diagnosis for congenital ichthyosis.

Daily application of emollients. Keratolytic agents, such as urea, salicylic acid, lactic acid ointments, topical retinoids. Systemic retinoids (isotretinoin, acitretin).

Special

Reference centers for severe cases.

6.1.4 Ichthyoses