7th June 2025

Ichthyosis

Ichthyosis is derived from the Greek work Ichthyosis which means ‘fish’ denoting the presence of fishy like scales on the skin

Aetiology

• Loss of function of the gene filaggrin gene function encoding for the protein filaggrin (FLG). 
  • It is essential in formation of keratohyalin granules which are found in the granular layer of epidermis. 
  • It is responsible for aggregating keratin filaments which covalently cross link and bind them together to form a condensed skin barrier. 
• The loss of the gene function results in the disruption in its barrier function as well as reduction/loss of the moisturizing function of the epidermal layer (Xerosis). 
• Excessive scaling forms as a result of the inability of the skin cells to remain hydrated as they move up through the epidermis. 
• As a compensatory repair mechanism, hyperkeratosis results.

Epidemiology

• Ichthyosis vulgaris is the most common inherited type of ichthyosis.
• Relatively common. Incidence in the British population is around 1/80-1/250.

Inheritance

• Autosomal semi-dominant condition
  • Individuals who inherit two alleles of the gene are much more severely affected than individuals who inherit a single allele.

Diagnosis

Diagnosis of ichthyosis is usually clinical diagnosis, based on history and examination findings.  

History

• Onset after birth/early childhood
• Possible improvement with age, warm weather 
• Family history
• Associated atopic diseases

Examination                    

• Distribution
  • Most commonly in the trunk and extensor extremities. Usually spares the skin folds (e.g. neck, axilla, elbow and knee crease)
• Morphology:
  • Scales: White/Grey fine scales 
  • Palmar hyper linearity: Pronunciation of major fissures as well as fissures on thenar eminence. Increase in minor fissures.
  • Keratosis pilaris: Rough, small bumps on the surface of the skin.
• For associated diseases Image Source: Wikimedia Commons (2017). Ichthyosis, Licensed under a creative commons licence. Available for free at: https://en.wikipedia.org/wiki/Ichthyosis#/media/File:Ichthyosis_(1).jpg (Accessed 22 May 2025).
• Corneal affection
• Atopic diseases

Histopathology

• Clinical diagnosis is usually sufficient
• Biopsy is usually taken from the extensor part of the arm/shin and shows a markedly reduced/absent granular layer in the epidermis. Electron microscopy shows abnormal keratohyalin granules.

Management

General measures

• Regular bathing and exfoliating 

Medical Management

• Emollients and moisturizers
• Keratolytics e.g. salicylic acid, are proved to be superior to simple emollients as evidenced by a systemic review of randomized controlled studies. 
• The use of topical steroids/calcipotriene/ retinoids are not usually indicated. 
• Oral retinoids are used for severe cases
• Management of complications
  • Skin infection, allergies, overheating
  • Higher incidence of atopic conditions may require specific management