Ichthyosis Vulgaris

Overview

Epidemiology

Ichthyosis vulgaris is the most common keratinization disorder.

• Incidence: 1 in 250 people
• No ethnic or sex predilection
• 95% of cases are hereditary.

Etiology

Hereditary ichthyosis vulgaris:

• Caused by loss-of-function mutations of the filaggrin (FLG) gene
• Autosomal dominant
• Variable penetrance

Acquired ichthyosis vulgaris:

• Associated malignancies:
  • Hodgkin’s disease
  • Multiple myeloma
  • Cutaneous T cell lymphoma
• Associated systemic diseases:
  • Systemic lupus erythematosus
  • AIDS
  • Celiac disease
  • Crohn’s disease
  • Hypothyroidism

Pathophysiology

• Normal filaggrin protein:
  • Responsible for aggregating and condensing keratin intermediate filaments in the lower stratum corneum
  • Degraded into water-retaining amino acids (histidine) → moisturizes skin and is photoprotective
• Mutations in FLG → abnormal filaggrin formation: 
  • Disrupted mechanical skin barrier → excessive water loss
  • Deficiency of histidine → loss of moisture and photoprotection

Clinical Presentation

Signs and symptoms

Clinical course:

• Hereditary ichthyosis vulgaris:
  • Skin appears and feels normal at birth.
  • Dry, scaly appearance begins in infancy or early childhood.
  • Seasonal variation:
    • Amelioration in warm, sunny weather
    • Exacerbation in cold, dry weather
  • A significant proportion of patients may have gradual improvement during adolescence.
  • A minority of patients will experience worsening with age.
• Acquired ichthyosis vulgaris: usually develops later in life

Skin findings:

• Scaling:
  • White or gray
  • Rough
  • Small
  • Irregular
  • Semi-adherent, centrally attached
• “Mosaic pattern” or “lizard skin” appearance
• Dry
• Hyperlinearity on palms and soles
• Keratosis pilaris

Location:

• Diffuse
• Extensor surfaces of the extremities and trunk are more often affected.
• Sparing of flexor and intertriginous surfaces

Associated with:

• Pruritus
• Fissuring
• Secondary infections

Associated conditions

• Atopic dermatitis
• Asthma
• Allergies

Diagnosis and Management

Diagnosis

The diagnosis is based on the clinical exam and family history. In patients with a milder phenotype, the following may be used:

• Skin biopsy: 
  • Taken from the thickest area of scaling
  • Findings:
    • Compact hyperkeratosis in the stratum corneum
    • Reduced or absent granular layer in the epidermis
    • Follicular plugging → keratosis pilaris
• Genetic testing:
  • Identify mutations in the FLG gene
  • Not routinely performed, but gives a definitive diagnosis

Management

There is no definitive treatment for ichthyosis vulgaris. The goal is to avoid excessive drying, remove scales, and improve skin appearance.

• Emollients and moisturizers:
  • Mainstay of management
  • Smooth and hydrate skin
• Keratolytics: aid in removing scales
• Topical retinoids (tretinoin):
  • Reduce the aggregation of abnormal keratinocytes
  • Suppresses keratin synthesis
  • Used to decrease scaling in resistant cases
• Management of underlying systemic conditions is required for acquired ichthyosis vulgaris.

Differential Diagnosis

• Atopic dermatitis: a chronic inflammatory disease of the skin, usually due to a combination of genetics, immunologic dysfunction, and environmental factors. Dry skin, erythematous lesions, and pruritus are common features. Unlike ichthyosis vulgaris, the flexural surfaces are usually involved. The diagnosis is clinical. Management includes trigger avoidance, moisturizers, and topical steroids.
• Psoriasis: a chronic T cell–mediated inflammatory disorder of the skin that can occur at any age, but usually in the 3rd or 6th decade of life. Patients often develop salmon-colored plaques with silvery scales, with pruritus on extensor surfaces. The diagnosis is clinical. Management depends on the extent of skin involvement and includes topical steroids, retinoids, calcineurin inhibitors, disease-modifying antirheumatic drugs, biologics, and phototherapy.
• X-linked ichthyosis: a mutation in the STS gene on the X chromosome, which results in steroid sulfatase deficiency. Patients develop dry, scaling, erythematous skin on extensor surfaces and scalp. Pruritus is usually absent. Patients may also have corneal opacities, cryptorchidism, and cognitive or behavioral disorders. The diagnosis is based on the clinical history, steroid sulfatase enzyme activity, and genetic testing. Management includes topical moisturizers, emollients, and retinoids.
• Harlequin ichthyosis: a rare congenital form of ichthyosis that is inherited in an autosomal recessive pattern. The condition presents at birth and causes thickening of the keratin layer of the stratum corneum. This produces yellow “armor-like” scales that restrict chest wall and extremity movement. Patients may develop severe respiratory difficulty, dehydration, and sepsis. The diagnosis is clinical, and management requires NICU support, humidification, emollients, and retinoids.