Ichthyosis Vulgaris

Ichthyosis vulgaris (IV) is the commonest inherited ichthyosis. It is a semidominant keratinisation disorder caused by loss-of-function mutations in the Filaggrin (FLG) gene on chromosome 1q21. Low filaggrin means few keratohyalin granules (the histological hallmark of IV), less Natural Moisturising Factor and therefore a dry, poorly hydrated stratum corneum. People with one faulty copy have a milder picture. Those with two faulty copies lack filaggrin, scale all over and are more prone to severe, persistent Atopic Dermatitis (Elias & Wakefield 2011).

Filaggrin [causes] Ichthyosis Vulgaris Ichthyosis Vulgaris [relates] Natural Moisturising Factor Ichthyosis Vulgaris [relates] Skin Barrier Dysfunction

What it looks like in a toddler. Fine (sometimes coarse) light-grey scale, stuck down in the centre, usually appears 2–6 months after birth. It is most marked on the shins, where it can look like a mosaic. The palms and soles are often hyperlinear (extra creases). Unlike eczema, IV itself is usually only mildly itchy and not inflamed. IV often co-occurs with Keratosis Pilaris. Diagnosis is mostly clinical, and the dry skin of AD can be hard to tell apart from IV (Siegfried & Hebert 2015).

Ichthyosis Vulgaris [relates] Keratosis Pilaris Ichthyosis Vulgaris [part-of] Differential Diagnosis of Toddler Eczema

Overlap with eczema. Siegfried & Hebert report that about half of people with IV develop AD. Elias & Wakefield put the figure at about two thirds with AD, allergic rhinitis and/or asthma. The figures measure different outcomes, so they do not truly conflict. IV is associated with earlier-onset and more severe AD and with atopy. In both IV and AD the skin’s Skin pH is raised. This activates kallikrein proteases that impair lipid secretion and promote Th2 inflammation. Elias & Wakefield therefore call IV a “forme fruste” (incomplete form) of AD: the same barrier defect, which becomes inflamed only when allergens get in or the skin meets extra stressors such as harsh soaps or low humidity. Birth-cohort data fit this. In ALSPAC, FLG null mutations were most strongly tied to early-onset-persistent eczema (OR 4.31) (Eczema Trajectories).

Ichthyosis Vulgaris [precedes] Atopic Dermatitis Ichthyosis Vulgaris [relates] Skin pH Filaggrin [relates] Eczema Trajectories

Practical care. There is no cure. Management is daily Emollient Therapy, and keratolytic humectants such as Urea Creams are used for scale in IV. Avoid high-pH soaps that worsen the barrier. In a toddler with both conditions, the eczema patches still need anti-inflammatory treatment (Topical Corticosteroids), whereas the scaly shins mainly need moisturiser. Higher-strength urea creams can sting broken or inflamed toddler skin, so they are better kept to intact scaly areas.

Emollient Therapy [treats] Ichthyosis Vulgaris Urea Creams [treats] Ichthyosis Vulgaris

Connections

• Filaggrin — FLG-deficiency disorder, source: Elias & Wakefield 2011
• Differential Diagnosis of Toddler Eczema — diffuse scaling look-alike or minor feature of AD, source: Siegfried & Hebert 2015
• Keratosis Pilaris — frequently co-occurs, source: Siegfried & Hebert 2015
• Atopic Dermatitis — ~half of IV patients develop AD; earlier, more severe onset, source: Siegfried & Hebert 2015
• Skin pH — raised stratum corneum pH as in AD, source: Elias & Wakefield 2011
• Natural Moisturising Factor — filaggrin breakdown supplies NMF, source: Elias & Wakefield 2011
• Urea Creams — urea-based emulsions used for IV scale, source: Piquero-Casals 2021
• ALSPAC — FLG and persistent eczema link, source: Paternoster 2018