Immunology · Year 2 · from Immunology
Case 2: Allergic Contact Dermatitis (Type IV Hypersensitivity)
Patient Demographics
- Age: 38 years old
- Sex: Female
- Ethnicity: Caucasian
Chief Complaint
Intensely itchy rash on neck and earlobes for 5 days
History of Present Illness
A 38-year-old woman presents with a severely pruritic rash that began on her earlobes 5 days ago and has spread to her neck and upper chest. The rash is characterized by small blisters and redness. She recently celebrated her 10th wedding anniversary and received new jewelry from her husband, including nickel-containing costume earrings and a necklace that she has worn daily for the past week. She has had similar but milder reactions to jewelry in the past.
Past Medical History
- History of "sensitive skin" to jewelry
- Seasonal allergic rhinitis
Physical Examination
- General: Uncomfortable due to pruritus, scratching affected areas
- Vital Signs: Normal
- Skin:
- Bilateral earlobes: Erythema, vesicles, weeping, crusting at earring sites
- Neck: Linear and geometric pattern of erythematous papules and vesicles corresponding to necklace contact
- Upper chest: Scattered erythematous papules extending beyond contact area
- No lesions on palms, soles, or mucous membranes
Diagnostic Testing
Patch testing performed at follow-up (48 and 96-hour readings):
| Allergen | 48-hour | 96-hour | Interpretation |
|---|---|---|---|
| Nickel sulfate | 2+ | 3+ | Positive (strong) |
| Cobalt chloride | 1+ | 2+ | Positive |
| Gold sodium thiosulfate | - | - | Negative |
| Fragrance mix | - | - | Negative |
| Balsam of Peru | - | - | Negative |
Diagnosis
Allergic Contact Dermatitis to Nickel (Type IV delayed-type hypersensitivity)
Discussion
Allergic contact dermatitis is a Type IV (cell-mediated) hypersensitivity reaction:
Pathophysiology:
- Sensitization phase: Nickel (hapten) penetrates skin, binds to carrier proteins
- Langerhans cells uptake hapten-protein complex, migrate to lymph nodes
- Present to naive T cells, generating hapten-specific memory T cells
- Elicitation phase: Re-exposure activates memory T cells at contact site
- T cells release IFN-gamma, TNF-alpha, recruiting inflammatory cells
- Keratinocyte apoptosis by CD8+ cytotoxic T cells
Why nickel allergy is so common:
- Nickel is the most common contact allergen worldwide
- Prevalence higher in women (ear piercing, jewelry exposure)
- Nickel found in: costume jewelry, belt buckles, watchbands, cell phones, coins, surgical instruments
Distinguishing allergic from irritant contact dermatitis:
| Feature | Allergic Contact | Irritant Contact |
|---|---|---|
| Mechanism | Immune (Type IV) | Direct cytotoxicity |
| Sensitization | Required | Not required |
| First exposure | No reaction | Can cause reaction |
| Timing | 24-96 hours | Immediate to hours |
| Distribution | May spread beyond contact | Limited to contact area |
| Symptoms | Pruritus | Burning, stinging |
Patch testing interpretation:
- 1+ = Erythema, infiltration
- 2+ = Erythema, papules, infiltration
- 3+ = Vesicles, bullae
Treatment
- Allergen avoidance: Remove nickel-containing jewelry; use nickel-free alternatives (surgical steel, titanium, 18K gold)
- Acute management: Topical corticosteroids (medium-high potency for body)
- Symptomatic relief: Oral antihistamines for pruritus
- Patient education:
- Check labels for nickel content
- Apply clear nail polish to metal surfaces that contact skin
- Nickel spot test kits available
- Occupational considerations: Some professions have higher nickel exposure