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Chronic rash

Specialties > Child health

Differential Diagnosis Schema 🧠

Eczema/Dermatitis

  • Atopic dermatitis: Chronic, relapsing itchy rash, often with a personal or family history of atopy (asthma, hay fever), common in flexural areas
  • Contact dermatitis: Localized rash following exposure to an irritant or allergen, often with a well-demarcated border
  • Seborrheic dermatitis: Greasy, scaly rash commonly affecting the scalp, face, and upper chest; associated with Malassezia yeast

Psoriasis

  • Chronic plaque psoriasis: Well-demarcated erythematous plaques with silvery scale, commonly on extensor surfaces (e.g., elbows, knees), scalp, and sacral region
  • Guttate psoriasis: Multiple small, drop-like lesions often following a streptococcal throat infection, more common in children and young adults
  • Pustular psoriasis: Pustules on an erythematous base, can be localized (e.g., palms, soles) or generalized, potentially life-threatening

Infectious Causes

  • Tinea corporis (ringworm): Annular, scaly plaques with central clearing and an active border, commonly found on non-hairy skin
  • Pityriasis rosea: Herald patch followed by a Christmas tree distribution of smaller lesions on the trunk, usually self-limiting
  • Chronic fungal infections: Erythematous, scaly lesions, often in moist areas (e.g., intertriginous zones), may involve nails (onychomycosis)

Autoimmune and Connective Tissue Diseases

  • Systemic lupus erythematosus (SLE): Malar rash (butterfly-shaped), photosensitivity, discoid lesions, often associated with systemic symptoms
  • Dermatomyositis: Heliotrope rash (violet discoloration of the eyelids), Gottron’s papules (over knuckles), associated with muscle weakness
  • Lichen planus: Pruritic, purple, polygonal papules, often on the wrists, lower back, and ankles; Wickham striae (white lines) on the lesions

Drug Eruptions

  • Fixed drug eruption: Single or multiple round, well-defined, erythematous patches that recur at the same site with re-exposure to the drug
  • Lichenoid drug eruption: Lichenoid papules and plaques, often indistinguishable from idiopathic lichen planus, commonly triggered by antihypertensives or NSAIDs
  • Stevens-Johnson syndrome/Toxic epidermal necrolysis: Severe mucocutaneous reactions, widespread purpuric macules or blisters, can be life-threatening

Key Points in History 🥼

Onset and Duration

  • Acute vs chronic: Chronic rashes last >6 weeks and suggest chronic inflammatory conditions like eczema, psoriasis, or lichen planus
  • Recurrent vs persistent: Recurrent rashes may suggest herpes simplex, erythema multiforme, or fixed drug eruption

Rash Characteristics

  • Distribution: Eczema often affects flexures, psoriasis on extensor surfaces; SLE may involve sun-exposed areas
  • Appearance: Papules, plaques, pustules, or vesicles can point towards differentials (e.g., pustules in psoriasis, vesicles in eczema)
  • Colour: Erythematous, violaceous, or hypopigmented lesions can be associated with different conditions (e.g., violaceous in lichen planus, erythematous in eczema)
  • Scaling: Present in conditions like psoriasis or tinea, absent in conditions like lichen planus or SLE
  • Pruritus: Common in eczema, lichen planus, and dermatitis herpetiformis

Background

  • Past medical history: Personal or family history of atopy (eczema, asthma, hay fever), autoimmune conditions, or chronic infections (e.g., HIV) may suggest specific rashes
  • Drug history: Recent changes in medication may indicate drug eruptions; long-term NSAID use can exacerbate psoriasis
  • Family history: Psoriasis, atopic dermatitis, and autoimmune diseases often have familial tendencies
  • Social history: Occupational exposure to irritants or allergens, lifestyle factors such as stress, smoking, and alcohol use
  • Travel history: Exposure to endemic infections (e.g., leishmaniasis), sun exposure in lupus

Possible Investigations 🌡️

Laboratory Tests

  • Full blood count: May show eosinophilia in atopic conditions or infection, anemia in chronic disease
  • Antinuclear antibodies (ANA): Positive in systemic lupus erythematosus and other autoimmune conditions
  • Patch testing: Useful in suspected allergic contact dermatitis to identify specific allergens
  • Skin biopsy: May be indicated for unclear diagnoses, shows characteristic histological features (e.g., psoriasis, lichen planus)
  • Serology: Useful in diagnosing infectious causes, such as syphilis or HIV

Imaging and Special Tests

  • Dermatoscopy: Can help in differentiating benign from malignant lesions, and in identifying specific patterns in rashes like psoriasis or lichen planus
  • Wood’s lamp: Useful in diagnosing fungal infections, vitiligo, or erythrasma
  • Photopatch testing: Indicated when photoaggravated contact dermatitis is suspected
  • Skin prick testing: Used for identifying immediate-type hypersensitivity reactions in suspected atopic dermatitis
  • Culture and sensitivity: May be required for suspected bacterial, viral, or fungal infections causing chronic rash

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Child health