Contact Dermatitis: Allergic

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ACD Basics - Skin's Delayed Fury

  • Definition: Allergic Contact Dermatitis (ACD) is an immune-mediated, delayed (Type IV) hypersensitivity reaction to an external allergen. Unlike Irritant Contact Dermatitis (ICD), which is direct non-immune tissue damage. 📌 ACD = Allergen Causes Delayed reaction.
  • Pathophysiology (Type IV Hypersensitivity):

⭐ ACD is a classic example of a Type IV hypersensitivity reaction mediated by T-lymphocytes.

Patch test reactions in allergic contact dermatitis

Allergen Parade - The Usual Suspects

📌 For common metals: No Chrome Contact (Nickel, Cobalt, Chromium).

AllergenCommon Sources (India Focus)Key Notes / Cross-reactions
NickelArtificial jewelry, coins, buckles, jean studsCross-reacts: Cobalt, Palladium
Potassium dichromateCement (construction), leather, paints, matchesCross-reacts: Cobalt
Paraphenylenediamine (PPD)Hair dyes, "black henna" tattoos, some textilesCross-reacts: Azo dyes, sulfonamides, PABA
Fragrance MixCosmetics, perfumes, soaps, toiletriesCross-reacts: Balsam of Peru, colophony
PreservativesCosmetics, creams (parabens, formaldehyde-releasers)Patch testing often needed
Parthenium hysterophorus"Congress grass" (common airborne weed)Significant plant dermatitis cause in India
UrushiolMango sap, marking nut (bhilawan), cashew shellFamily: Anacardiaceae; potent sensitizer
Topical MedicationsNeomycin creams, some topical corticosteroidsNeomycin cross-reacts: other aminoglycosides

Parthenium dermatitis is a significant cause of airborne contact dermatitis in India.

Rash Report - Itch & Tell

  • Onset: 24-72 hours post-exposure in sensitized individuals.
  • Morphology:
    • Acute: Erythema, edema, vesicles/bullae (may be tense), oozing, intense pruritus.
    • Subacute: Scaling, crusting, less vesicular, resolving erythema.
    • Chronic: Lichenification (thickened skin), fissuring, hyper/hypopigmentation, dryness.
  • Distribution:
    • Often sharply demarcated, localized to site of direct contact.
    • Linear streaks: Plant contact (e.g., Poison Ivy, Parthenium - 📌 think "streaky rash from a leafy dash").
    • Specific Patterns: Consider: Earlobes (nickel), eyelids (cosmetics, nail polish transfer), feet (footwear components like chromates, rubber). Allergic Contact Dermatitis: Overview

⭐ The presence of well-demarcated, eczematous lesions in an area of allergen exposure is highly suggestive of ACD.

Patch Test Puzzles - Finding Culprits

  • History is Key: Occupation, hobbies, cosmetics, topicals, clothing, jewelry.
  • Patch Testing: Gold Standard
    • Identifies specific allergen.
    • Technique: Allergens applied, readings at 48 & 72/96 hrs.
    • Interpretation: + (weak), ++ (strong), +++ (extreme), IR (irritant).
    • Series: Indian Standard Series. Allergy Patch Test Positive Reactions
  • Differential Diagnosis:
    • Irritant Contact Dermatitis (ICD)
    • Atopic Dermatitis
    • Seborrheic Dermatitis
    • Psoriasis
    • Fungal infections

⭐ A positive patch test must be clinically relevant to the patient's dermatitis to confirm ACD.

Soothe & Shield - Calming Chaos

  • Cornerstone: Allergen identification & strict avoidance.
  • Patient Education: Allergen sources, cross-reactants, alternative products.
  • Topical Therapy:
    • Corticosteroids: Potency based on site/severity.
    • Topical Calcineurin Inhibitors (TCIs): e.g., Tacrolimus, Pimecrolimus for sensitive areas, long-term use.
  • Systemic Therapy (Severe/Widespread ACD):
    • Oral Corticosteroids: e.g., Prednisolone $0.5-1 \text{ mg/kg/day}$ tapered over 2-3 weeks.
    • Antihistamines: For pruritus.
  • Supportive Care: Emollients, wet compresses.

⭐ Short courses of potent topical steroids are preferred over long courses of weaker steroids to minimize side effects.

High‑Yield Points - ⚡ Biggest Takeaways

  • Type IV hypersensitivity reaction, delayed onset (24-72 hours post-exposure).
  • Common allergens: nickel (jewelry), poison ivy (urushiol), fragrances, preservatives, PPD (hair dye).
  • Clinical: intensely pruritic, erythematous papules/vesicles, well-demarcated at contact site.
  • Patch testing is gold standard for diagnosis, identifies specific allergen.
  • Management: strict allergen avoidance, topical corticosteroids (mainstay), emollients; systemic steroids for severe/widespread.
  • Chronic ACD: lichenification, scaling, fissuring; may become generalized or id reaction (autosensitization).

Practice Questions: Contact Dermatitis: Allergic

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Dermatitis may be a clinical manifestation of deficiency states of all of the following nutrients except -

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Flashcards: Contact Dermatitis: Allergic

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_____ dermatitis presents with a pruritic, oozing rash with vesicles and edema due to a type IV HSR

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_____ dermatitis presents with a pruritic, oozing rash with vesicles and edema due to a type IV HSR

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