The term "ichthyosis" implies a generalized scaly dermatosis, without the component of erythema. The ichthyoses are disorders of cornification and are classified as inherited or acquired. Hereditary ichthyosis is further classified as syndromic and non-syndromic. Ichthyosis vulgaris (IV) is an inherited form of non-syndromic ichthyosis, with a very early age of onset. Ichthyosis vulgaris is associated with loss of function FLG gene mutations, which leads to a defective skin barrier. Historically, the first case of ichthyosis vulgaris was described in 1806 as "ichthyose nacrée." Willan introduced the term "ichthyosis," derived from the Greek root "ichthy," meaning fish.
Hereditary ichthyosis (HI) is an autosomal dominant genetic disorder that develops in early childhood. Whereas, acquired ichthyosis (AI) may be associated with underlying cancer, such as Hodgkin’s disease, multiple myeloma, cutaneous T cell lymphoma or with an underlying systemic disorder such as systemic lupus erythematosus, acquired immunodeficiency syndrome (AIDS) or health conditions that reduce lipid and vitamin absorption including celiac disease and Crohn’s disease. Certain medications have been reported to induce AI, such as cholesterol-lowering agents, allopurinol, targeted cancer therapy (EGFR inhibitors, BRAF inhibitors), and many more.
IV is the most common ichthyosis, with an estimated prevalence of 1 in 100 to 250. The mode of inheritance is autosomal semi-dominant with a milder phenotype in heterozygous individuals. The overall penetrance is 80%-95%. The age of onset is in infancy, with the majority of patients having clearly characteristic manifestations by 5 years of age. Sex or ethnic predilection has not been observed.
The central event in the pathogenesis of ichthyosis is the disruption of the epidermal barrier. The integrity of the cornified cell envelope is responsible for the maintenance of the barrier function of the skin. In ichthyosis vulgaris, loss of function mutations of the FLG gene leads to defective filaggrin formation, which is an important component of the cornified cell envelope.
The stratum granulosum is characterized by keratohyaline granules. Profilaggrin is an important component of these granules. During keratinocyte differentiation, profilaggrin is cleaved into filaggrin peptides, which in turn, are responsible for the alignment of keratin intermediate filaments. Ultimately, these complexes get cross-linked and are responsible for the compactness of the cell envelope.
Loss of function mutations of FLG, commonly, the R501X and c.2282del4, lead to an absolute or relative deficiency of filaggrin. This causes a disruption of the mechanical barrier, leading to excessive transepidermal water loss. Moreover, it also disrupts the immunological barrier of the skin by increasing the propensity of penetration of allergens and microorganisms and the resultant cutaneous inflammatory responses. Hence, patients of ichthyosis vulgaris have a higher tendency of atopic dermatitis, as well as hand eczema, irritant contact dermatitis, and allergic contact dermatitis.
In normal epidermis, filaggrin is eventually degraded into water-retaining amino acids, in particular histidine, that serves as a natural moisturizer. FLG mutations cause a deficiency of histidine and its metabolites, one of which is urocanic acid, which is a natural photoprotective agent. Hence in ichthyosis vulgaris, there is an upregulation in UVB induced synthesis of vitamin D, ultimately leading to an increase in serum vitamin D levels.
The epidermis shows a mild orthokeratotic hyperkeratosis with or without hypo/agranulosis. There is an absence of inflammatory infiltrate.
Electron microscopy is diagnostic, which shows absent or structurally abnormal keratohyaline granules.
The spectrum of clinical features of ichthyosis vulgaris varies from mild xerosis to large adherent scales (lizard skin). Heterozygous FLG mutations usually present in infancy or early childhood. Fine, whitish, scales with predominant extensor distribution is the hallmark manifestation. The flexural areas are typically spared, due to the presence of humidity in these areas. In homozygous individuals, the manifestations are much more severe with large, centrally adherent scales, especially on the lower limbs and trunk and palmoplantar fissuring and hyperkeratosis. Severe cases may show facial involvement with mild ectropion and perioral fissuring. The scalp shows extensive scaling. Nails and mucosa are usually unaffected.
The scaling shows a seasonal exacerbation in winter and is relatively improved in the summer and in humid climates. Even though it persists lifelong, ichthyosis vulgaris tends to improve with age.
About 25% to 50% of patients of ichthyosis vulgaris show associated atopic dermatitis, asthma, and hay fever, with filaggrin deficiency being the major predisposing factor. Keratosis pilaris and palmoplantar hyperlinearity are other associated features.
A high suspicion for ichthyosis vulgaris should be included in the evaluation of patients consulting for skin disorders. A family history of a similar dermatosis and a thorough inspection of the skin should be obtained. The diagnosis of ichthyosis vulgaris is based on several factors. These factors include the time of onset of clinical symptoms, the skin phenotype (color, scale pattern, the presence of erythroderma, a collodion membrane at birth), associated cutaneous manifestations, family history and hereditary transmission, histopathologic findings, absence or presence of extracutaneous manifestations, and genetic testing. Genetic testing may be beneficial for the confirmation of diagnosis and for genetic counseling.
The main treatment approach of both HI and AI includes hydration of the skin and application of an ointment to prevent evaporation. Urea-based emulsion, composed of 10% urea, natural moisturizing factors, and ceramides used twice daily, represents an effective therapeutic option. Topical retinoids and alpha-hydroxy acids may be helpful for some patients. Topical retinoids act by reducing cohesiveness of epithelial cells, stimulating mitosis and turnover, and suppressing keratin synthesis. Mild topical steroids may be useful in the case of pruritus. Treatment of the underlying systemic condition may improve the AI.
Differential diagnoses of ichthyosis vulgaris include:
HI has an excellent prognosis as symptoms usually improve with age. The prognosis of AI depends on the severity of the underlying systemic disease or cancer.
As a conclusion of the study, collective therapeutic education programs seem to be very interesting. In general, the contributions of a therapeutic education program to the management of genodermatoses can help in building trust between patients, their families, and carers and promote the encouragement of self-expression and the autonomy of patients and their families.
Ichthyosis has a significant psychological impact on each patient, as almost all visible skin surfaces are affected. This frequently leads to social rejection. The management of these patients is difficult, and the treatment is expensive and time-consuming. Collaboration between primary clinicians, dermatologists, psychiatrists, nurses, and social workers is recommended.
|||Takeichi T,Akiyama M, Inherited ichthyosis: Non-syndromic forms. The Journal of dermatology. 2016 Mar; [PubMed PMID: 26945532]|
|||Thyssen JP,Kezic S, Causes of epidermal filaggrin reduction and their role in the pathogenesis of atopic dermatitis. The Journal of allergy and clinical immunology. 2014 Oct; [PubMed PMID: 25065719]|
|||Dar NR,Raza N,Khan A,Amin MU, Paraneoplastic Addisonian pigmentation and acquired ichthyosis as presenting features of multiple myeloma. Journal of the College of Physicians and Surgeons--Pakistan : JCPSP. 2011 Jan; [PubMed PMID: 21276385]|
|||Biver-Dalle C,Gil H,Méaux-Ruault N,Mermet-Ginet I,Aubin F,Humbert P,Magy-Bertrand N, [Acquired ichthyosis and livedoid palmoplantar keratoderma: two unusual skin manifestations of systemic lupus erythematosus]. La Revue de medecine interne. 2012 Mar; [PubMed PMID: 21429634]|
|||Oji V,Seller N,Sandilands A,Gruber R,Gerss J,Hüffmeier U,Hamm H,Emmert S,Aufenvenne K,Metze D,Luger T,Loser K,Hausser I,Traupe H,McLean WH, Ichthyosis vulgaris: novel FLG mutations in the German population and high presence of CD1a cells in the epidermis of the atopic subgroup. The British journal of dermatology. 2009 Apr; [PubMed PMID: 19183181]|
|||Gruber R,Janecke AR,Fauth C,Utermann G,Fritsch PO,Schmuth M, Filaggrin mutations p.R501X and c.2282del4 in ichthyosis vulgaris. European journal of human genetics : EJHG. 2007 Feb; [PubMed PMID: 17164798]|
|||Hanifin JM, Evolving concepts of pathogenesis in atopic dermatitis and other eczemas. The Journal of investigative dermatology. 2009 Feb; [PubMed PMID: 18719604]|
|||Winge MC,Hoppe T,Berne B,Vahlquist A,Nordenskjöld M,Bradley M,Törmä H, Filaggrin genotype determines functional and molecular alterations in skin of patients with atopic dermatitis and ichthyosis vulgaris. PloS one. 2011; [PubMed PMID: 22164253]|
|||Kang TW,Lee JS,Oh SW,Kim SC, Filaggrin mutation c.3321delA in a Korean patient with ichthyosis vulgaris and atopic dermatitis. Dermatology (Basel, Switzerland). 2009; [PubMed PMID: 18841000]|
|||Xiong Z,Luo S,Xu X,Zhang L,Peng H,Li W,Xue J,Chen X,Hu Z,Xia K, Novel FLG mutations associated with ichthyosis vulgaris in the Chinese population. Clinical and experimental dermatology. 2012 Mar; [PubMed PMID: 22299762]|
|||Zhong W,Cui B,Zhang Y,Jiang H,Wei S,Bu L,Zhao G,Hu L,Kong X, Linkage analysis suggests a locus of ichthyosis vulgaris on 1q22. Journal of human genetics. 2003; [PubMed PMID: 12838398]|
|||Liu P,Yang Q,Wang X,Feng A,Yang T,Yang R,Wang P,Yuang M,Liu M,Liu JY,Wang QK, Identification of a genetic locus for ichthyosis vulgaris on chromosome 10q22.3-q24.2. The Journal of investigative dermatology. 2008 Jun; [PubMed PMID: 18079749]|
|||Benintende C,Boscaglia S,Dinotta F,Lacarrubba F,Micali G, Treatment of ichthyosis vulgaris with a urea-based emulsion: videodermatoscopy and confocal microscopy evaluation. Giornale italiano di dermatologia e venereologia : organo ufficiale, Societa italiana di dermatologia e sifilografia. 2017 Dec; [PubMed PMID: 29050444]|
|||Haas AA,Arndt KA, Selected therapeutic applications of topical tretinoin. Journal of the American Academy of Dermatology. 1986 Oct; [PubMed PMID: 3534024]|