Ichthyosis Vulgaris

Ichthyosis vulgaris is the commonest inherited disorder of keratinisation, caused by loss-of-function mutations in the filaggrin gene (FLG), with semi-dominant inheritance.

• Prevalence is about 1 in 250 (up to 1 in 100 in some groups). Onset after 3 months of age, worst in childhood, and may improve in summer and with age.
• Strongly associated with atopic dermatitis, asthma, allergic rhinitis, and keratosis pilaris, and with food allergy.
• Pathogenesis: decreased filaggrin leads to impaired skin barrier, reduced natural moisturising factors, and dry skin.
• Distinguish from X-linked ichthyosis (steroid sulfatase deficiency) and acquired ichthyosis (lymphoma, HIV, hypothyroidism, sarcoidosis, drugs).

• Fine white to grey scale on extensor limbs and trunk, with sparing of flexural creases, face (mild), and scalp.
• Hyperlinear palms and soles, keratosis pilaris, and xerosis, with fissures in winter.
• Pruritus, eczema, and recurrent skin infection.
• X-linked ichthyosis for comparison: large, dark brown scales including flexures and neck, corneal opacities, cryptorchidism, males only.

• Clinical diagnosis based on typical scaling, family history, and palmar hyperlinearity.
• Histology: absent or reduced granular layer, hyperkeratosis.
• Genetic testing for FLG null mutations (R501X, 2282del4) if uncertain.
• Check steroid sulfatase (STS) activity or STS gene deletion in boys with severe scaling, and thyroid function, lymphoma screen, and HIV test for adult onset ichthyosis.
• Exclude eczema, scabies, hypothyroidism, and other genetic ichthyoses.

• Regular bathing followed by immediate emollients (petrolatum, ceramide containing creams) twice daily.
• Keratolytics/humectants: urea 10 to 20% cream (use lower strength in children), lactic acid 5 to 12% (ammonium lactate), salicylic acid 2 to 6% (avoid large areas in infants because of toxicity), and propylene glycol 40 to 60% in water.
• Topical retinoids (tretinoin 0.025%) in refractory cases; mild topical steroids for associated eczema.
• Humidified environment, avoid harsh soaps, and wear cotton clothing.
• Oral retinoids (acitretin) are rarely needed in ichthyosis vulgaris.
• Treat secondary infection, optimise atopic disease, and counsel on genetic transmission.