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Ichthyosis hystrix of Curth-Macklin
Ichthyosis hystrix of Curth-Macklin (IHCM) is a rare type of keratinopathic ichthyosis (see this term) that is characterized by the presence of severe hyperkeratotic lesions and palmoplantar keratoderma (PPK, see this term).
Prevalence is unknown. Six families and sporadic cases have been reported to date.
The skin is usually normal at birth. The disease starts in early childhood with severe hyperkeratosis of yellow-brown or grey color, and of spiky, cobblestone-like (hystrix) or verrucous appearance. Hyperkeratosis is often diffuse and more pronounced on extensor areas of the limbs, extremities and the trunk. Lesions may also be nevoid following the lines of Blaschko. Patients are also affected with striate or diffuse PPK. As the disease progresses, PPK worsens and results in deep bleeding, painful fissures and cracks. In severe cases, PPK can also lead to contractures, gangrene and loss of digits. The skin is malodorous and frequently infected. Nail dystrophy may be present. Contrary to other keratinopathic ichthyoses, no skin fragility/blister formation or erythroderma is present.
IHCM results from heterozygous frameshift mutation in a section of the KRT1 gene encoding keratin 1 (K1). These mutations lead to an abnormal supramolecular organization of keratin intermediate filaments and may be related to defects in cytoplasmic trafficking and integrity of cellular structures such as organelles and nucleus.
Diagnosis is based on clinical examination and on histological examination of skin lesion biopsies revealing papillomatous hyperplasia with hyperorthokeratosis and hypergranulosis. Electron microscopy shows keratin intermediate filaments forming continuous perinuclear shells, presence of perinuclear vacuoles and binucleate keratinocytes.
Differential diagnosis includes other forms of keratinopathic ichthyosis such as epidermolytic ichthyosis, as well as epidermolytic palmoplantar keratoderma, erythrokeratodermia variabilis, and KID syndrome (see these terms).
Molecular prenatal diagnosis is available for affected families.
Transmission is autosomal dominant but some sporadic cases have been reported. The risk for an affected parent to have an affected child is of 50%.
Management and treatment
Management is symptomatic and life-long. Oral and systemic keratolytics can improve localized hyperkeratotic lesions by exfoliating and increasing the moisture of the skin.
Life expectancy is normal. However, the unaesthetic and malodorous aspects of the skin, the pain and bleeding related to PPK, and infections lead to functional disabilities and a greatly reduced quality of life.