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Integumentary system ORGAN SYSTEMS

Atopic dermatitis

Introduction

Chronic inflammatory skin condition characterized by pruritic, erythematous, and scaly skin lesions often localized to the flexural surfaces of the body.

  • Atopy: Localised type I hypersensitivity reaction
  • M/C chronic inflammatory skin disease
  • Can present with asthma & allergic rhinitis as part of an allergic triad
    • ~30% children with atopic dermatitis develop asthma later in life

Epidemiology

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Global prevalence of atopic dermatitis symptoms | Weidinger, S., Beck, L. A., Bieber, T., Kabashima, K., & Irvine, A. D. (2018). Atopic dermatitis. Nature Reviews Disease Primers, 4(1), 1. https://doi.org/10.1038/s41572-018-0001-z

Aetiology

Genetic factors:

  • Flaggrin gene (strongest known genetic risk factor)
    • Filaggrin gene mutations give rise to functional impairments in the filaggrin protein and thereby disrupt the skin barrier.
    • Clinical expression of such impairments is dry skin with fissures and a higher risk of eczema.
  • Family history of atopy:
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Illustration showing the three associated allergy-related medical conditions referred to as the ‘atopic triad’; atopic asthma, atopic dermatitis and allergic rhinitis (hayfever). | 7mike5000 – CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24893840

Environmental factors:

  • Hygiene hypothesis (decrease in early childhood exposure to prototypical infections, such as hepatitis A and tuberculosis, has increased susceptibility to atopic diseases)
  • Other possible triggers:
    • Wollen clothing
    • Hot water & long baths
    • Infections (esp. Staphylococci)
    • Food allergy
    • Contact urticaria
    • Stress

Syndromic associations:

  • Atopic triad: Atopic dermatitis, asthma, allergic rhinitis
  • Hyper IgE syndrome (common autosomal dominant form, Job syndrome)
  • Wiskott-Aldrich syndrome (triad: eczema, thrombocytopenia, immunodeficiency)

Pathophysiology

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Histopathology:

  • Acute atopic eczema:
    • Intercellular oedema
    • Perivascular infiltrates primarily of lymphocytes
    • Parakeratosis (retention of the nuclei of the keratinocytes as they ascend into the stratum corneum)
  • Chronic eczema:
    • Hyperkeratosis (thickened stratum corneum)
    • Acanthosis (thickened stratum spinosum)
    • Sparse lymphocytic infiltrates

Clinical features

Presents as early onset of itchy eczema localised at typical sites such as the flexures of the elbows and knees in an atopic patient or in a person with a familial predisposition to atopic disease.

Eczema characterised by lively red infiltrate with oedema, vesicles, oozing, and crusting; lichenification, excoriations, papules, and nodules dominate the subacute and chronic form.

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Atopic dermatitis on the flexural surface of the arm. | Berke, R., Singh, A., & Guralnick, M. (2012). Atopic dermatitis: an overview. American Family Physician, 86(1), 35–42.

Distribution:

One of the few dermatoses that changes distribution with age.
  • Infantile AD (2 months – 2 years): Red papules, eczemathous eruption
    • Face, scalp, extensor aspects
  • Childhood AD (2 years – puberty): Red, scaly papules & plaques
    • Flexural distribution: Antecubital fossa (M/C), knee flexure
  • Adult AD (puberty onwards): Lichenification
    • Flexural distribution

Clinical stages:

  • Acute phase: Vesicular, weeping, crusting eruption
  • Subacute phase: Dry, scaly, erythematous papules and plaques
  • Chronic phase: Lichenification from repeated scratching
    • “The itch that rashes”: Itching followed by rashes

Skin changes:

  • Xerosis (dry skin): Due to ↓ water content + excessive water loss through epidermis
  • Ichthyosis (fish-like scales without inflammation)
  • White dermographism or skin-writing (hives at scratch site)
  • Headlight sign (sparing of periorbital, parinasal & perioral areas)

Ocular changes:

  • Keratoconus
  • Dennie-Morgan fold (double skinfold underneath inferior eyelid)
  • Anterior shield cataract (subcapsular)
  • Hertoghes sign (lateral madarosis)

Special manifestations:

  • Pityriasis alba (commonly occurs in children)
    • Characterized by hypopigmented, poorly demarcated plaques with fine scale.
  • Keratosis pilaris
    • Allergy which manifests as small, rough keratotic papules particularly on the upper arms and thighs 

Complications

Secondary bacterial infection from skin flora:

  • Impetigo: Staphylococcus and Streptococcus
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Impetigo is most often caused by S. aureus or Streptococcus pyogenes and is characterized by erythema, edema, and tenderness, often with honey-yellow crusting.

Herpes simplex virus infection:

  • Kaposi varicelliform eruption or eczema herpeticum
    • Widespread vesicular eruption, typically localised to the face, scalp, and upper chest

Other complications:

  • Scars (from picking and scratching)
  • Chronic postinflammatory skin changes, and skin atrophy
    • From long-term treatment with topical corticosteroids

Diagnosis

Hanifin & Rajka diagnostic criteria (1980):

  • Pruritus (hallmark feature)
  • Eczema with typical morphology and age-specific pattern:
    • Infantile form: Extensors
    • Childhood form: Flexors
  • Chronic/chronically relapsing dermatoses
  • Personal/family history of atopy
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Essential components of major and minor criteria in proposing diagnostic criteria of atopic dermatitis. | Lee, S.-C., & REACH, C. of K. A. D. A. for. (2016). Various diagnostic criteria for atopic dermatitis (AD): A proposal of Reliable Estimation of Atopic Dermatitis in Childhood (REACH) criteria, a novel questionnaire-based diagnostic tool for AD. The Journal of Dermatology, 43(4), 376–384. https://doi.org/10.1111/1346-8138.13264

Differential diagnosis:

  • Scabies
  • Seborrheic dermatitis
  • Contact dermatitis

Management

Atopic dermatitis is not curable, and many patients will experience a chronic course of the disease.

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A simplified, stepwise algorithm for the treatment of AD | Kapur, S., Watson, W., & Carr, S. (2018). Atopic dermatitis. Allergy, asthma, and clinical immunology : official journal of the Canadian Society of Allergy and Clinical Immunology, 14(Suppl 2), 52. doi:10.1186/s13223-018-0281-6

Newer drugs:

  • Mild-moderate AD: Crisaborole (PD-4 inhibitor)
  • Moderate-severe AD: Dupirumab (monoclonal antibody, IL-4 inhibitor)

Summary:

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Weidinger, S., Beck, L. A., Bieber, T., Kabashima, K., & Irvine, A. D. (2018). Atopic dermatitis. Nature Reviews Disease Primers, 4(1), 1. https://doi.org/10.1038/s41572-018-0001-z

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