Contact Dermatitis Clinical Overview
I. The "On-Call" Snapshot
Clinical Significance in Malaysia: Extremely common due to occupational exposures (healthcare, construction, cleaning services) and the widespread use of various traditional and cosmetic products. A core competency for any junior doctor.
High-Yield Definition: An inflammatory eczematous skin reaction resulting from direct contact of a substance with the epidermis. It is broadly divided into irritant and allergic types. (Source: UpToDate)
Clinical One-Liner: The skin is inflamed because it touched something it dislikes—either because the substance is inherently damaging (irritant) or because the immune system overreacted to it (allergic).
II. Etiology & Risk Factors
Etiology:
Irritant Contact Dermatitis (ICD): Accounts for ~80% of cases. A non-immunologic inflammation caused by the direct cytotoxic effect of a substance on keratinocytes. It is dose- and duration-dependent.
Allergic Contact Dermatitis (ACD): A delayed-type (Type IV) hypersensitivity reaction to an allergen. Requires prior sensitisation.
Risk Factors (Local Context):
Occupation:
Healthcare workers (latex gloves, antiseptics, sanitisers).
Construction workers (wet cement, chromates).
Cleaners/Food handlers (detergents, prolonged "wet work").
Hairdressers (dyes like paraphenylenediamine (PPD), bleach).
Atopic Dermatitis: A pre-existing skin barrier dysfunction increases susceptibility.
Common Exposures:
Nickel (imitation jewellery, belt buckles, phone casings).
Fragrances and preservatives in cosmetics and skincare.
Topical medications (e.g., neomycin).
Plants and traditional remedies ("herba").
III. Quick Pathophysiology
Irritant (ICD): The chemical directly strips epidermal lipids and damages cell membranes. This breaches the skin barrier, leading to transepidermal water loss and allowing deeper penetration of irritants, causing direct inflammation. Think of it as a low-grade chemical burn.
Allergic (ACD): A two-phase immunologic process.
Sensitisation: A low-molecular-weight hapten penetrates the skin, binds to a skin protein, and is processed by Langerhans cells. These cells present the antigen to T-cells in regional lymph nodes, creating memory T-cells. This phase is asymptomatic.
Elicitation: Upon re-exposure, sensitised memory T-cells recognise the antigen, triggering a cascade of cytokine release. This leads to the recruitment of inflammatory cells and the clinical appearance of eczema within 12-72 hours.
IV. Classification
Primary (By Etiology):
Irritant Contact Dermatitis (ICD)
Allergic Contact Dermatitis (ACD)
Temporal (By Morphology):
Acute: Vesicles, bullae, intense erythema, oedema.
Subacute: Less oedema and vesiculation; scaling and crusting become prominent.
Chronic: Lichenification (skin thickening), fissuring, and scaling from repeated exposure and scratching.
V. Clinical Assessment
🚩 Red Flags & Immediate Actions:
Widespread Erythroderma (>90% BSA): Risk of massive fluid loss, electrolyte imbalance, secondary infection, and thermoregulatory failure.
Action: Escalate to senior, admit, secure IV access, monitor vitals and urine output. This is a dermatological emergency.
Superimposed Bacterial Infection (Impetiginisation): Weeping, honey-coloured crusts, pustules, fever.
Action: Swab for C&S. Start empirical antibiotics (e.g., Cloxacillin or Clindamycin) after discussing with your senior.
Facial/Eyelid Involvement with Severe Oedema: Can compromise vision or airway.
Action: Escalate immediately. Will likely require systemic steroids.
History:
Key Diagnostic Clues:
A rash with a bizarre, geometric, or sharply demarcated border corresponding to an area of contact (e.g., watch strap, necklace line, waistband).
A clear temporal relationship between exposure to a new substance and the onset of the rash.
Crucial question: "What are all the things that have touched your skin in this area recently? Think about work, hobbies, new soaps, lotions, or medications."
Symptom Breakdown:
Common (>50%): Pruritus (the hallmark, especially in ACD), erythema, scaling. Stinging or burning pain is more suggestive of ICD.
Pertinent Negatives:
Absence of systemic symptoms like fever or arthralgia (unless secondarily infected).
Absence of a rash in non-exposed areas.
Physical Examination (OSCE Approach):
General Inspection: Note the distribution. Is it on sun-exposed areas (photodermatitis)? Acral areas (hands/feet)? Areas covered by jewellery?
Vitals: Typically normal. Fever suggests superinfection.
Disease-Specific Examination (Skin):
Look (Morphology & Distribution): The pattern is your biggest clue. Linear streaks suggest plant contact (e.g., poison ivy). A square patch under a plaster. Symmetrical involvement of both earlobes from earrings.
Positive Findings: A sharply marginated eczematous eruption that maps perfectly to a plausible external contactant.
Pertinent Negatives: Check for nail pitting or silvery scales (psoriasis), target lesions (erythema multiforme), or burrows (scabies).
Clinical Pearl: If you see a rash with straight lines, it is contact dermatitis until proven otherwise. The body does not spontaneously create right angles.
VI. Diagnostic Workflow
Differential Diagnosis:
Atopic Dermatitis:
Points For: Eczematous, pruritic rash.
Points Against: Typically starts in childhood, has a background of atopy (asthma, allergic rhinitis), and affects flexural areas (antecubital, popliteal fossae).
How to Differentiate: Clinical history and distribution. Patch testing can confirm an allergic contact component.
Seborrhoeic Dermatitis:
Points For: Erythema and scale.
Points Against: Affects sebum-rich areas (scalp, eyebrows, nasolabial folds, chest); scales are typically greasy and yellowish.
How to Differentiate: Location and character of the scales.
Tinea Corporis (Fungal Infection):
Points For: Erythematous, scaly, pruritic patch.
Points Against: Typically an annular (ring-shaped) plaque with a raised, active border and central clearing.
How to Differentiate: Skin scraping for KOH microscopy will show fungal hyphae.
Investigations Plan:
Bedside: None. This is a clinical diagnosis.
First-Line Labs & Imaging: Not required for localised, uncomplicated cases. If superinfection is suspected, FBC and CRP may be useful.
Confirmatory / Gold Standard: Allergen patch testing. This is the definitive investigation for ACD. Performed by a dermatologist once the acute dermatitis has resolved. Antigens are applied to the back and read at 48 and 96 hours.
VII. Staging & Severity Assessment
Severity is determined clinically based on:
Body Surface Area (BSA): Localised (<5% BSA) vs. Widespread (>20% BSA).
Symptom Intensity: Pruritus, pain, sleep disturbance.
Morphology: Erythema only vs. vesiculation and weeping.
Impact on Quality of Life (QoL): Effect on work and daily activities.
VIII. Management Plan
A. Principle of Management:
IDENTIFY and REMOVE the offending agent. This is the single most important step.
RESTORE the skin barrier with emollients.
REDUCE inflammation and pruritus.
B. Immediate Stabilisation (The ABCDE Plan):
Not applicable for typical localised contact dermatitis. This is a chronic outpatient condition unless red flags (e.g., erythroderma) are present.
C. Definitive Treatment (The Ward Round Plan):
Non-Pharmacological (Cornerstone of therapy):
Avoidance: Meticulous patient education on avoiding the identified irritant/allergen.
Emollients: Apply liberally and frequently (e.g., aqueous cream, cetomacrogol). This restores the skin barrier.
Protective measures: Use of gloves, barrier creams for occupational exposure.
Pharmacological:
Topical Corticosteroids: The mainstay. Match potency to body site and severity.
Mild Potency (e.g., Hydrocortisone 1%): For face, genitalia, flexures.
Moderate Potency (e.g., Betamethasone valerate 0.1%): For trunk, limbs.
Potent/Very Potent (e.g., Clobetasol propionate 0.05%): For palms, soles, lichenified plaques.
Course: Apply OD or BD for 1-2 weeks, then wean down.
Topical Calcineurin Inhibitors (Tacrolimus, Pimecromilus): Second-line. Good for sensitive sites where steroid atrophy is a concern (e.g., face, eyelids).
Systemic Therapy (For severe, widespread cases):
Oral Corticosteroids: Prednisolone 0.5 mg/kg (e.g., 30-40mg OM) for a short course, tapered over 2-3 weeks to prevent rebound.
Antihistamines: Primarily for sedation to help with nocturnal pruritus (e.g., hydroxyzine).
IX. Complications
Immediate/Short-Term: Secondary bacterial infection (Staphylococcus/Streptococcus).
Long-Term:
Lichen simplex chronicus (from persistent scratching).
Post-inflammatory hyper- or hypopigmentation.
Chronic, persistent dermatitis, especially with continued occupational exposure.
Psychosocial impact from chronic pruritus and cosmetic disfigurement.
X. Prognosis
Excellent if the causative agent is identified and strictly avoided.
Can become a chronic, relapsing condition if the trigger cannot be removed, leading to significant impact on quality of life and ability to work.
XI. How to Present to Your Senior
(S) Situation: "Dr, I'm reviewing Mr. Tan, a 50-year-old cleaner in the clinic, who has a severe, itchy rash on both hands for the past week."
(B) Background: "He has been a cleaner for 20 years but started using a new industrial detergent 2 weeks ago. The rash is confined to his hands and forearms. No history of atopy."
(A) Assessment: "On examination, there is a well-demarcated erythema with vesiculation and some fissuring over the dorsum of both hands, stopping abruptly mid-forearm. Vitals are stable. My impression is a severe acute irritant contact dermatitis."
(R) Recommendation: "I plan to provide an MC, educate him on avoiding the agent, and start treatment with a potent topical steroid like Clobetasol and frequent emollients. I think he also needs a short course of oral prednisolone. Do you agree?"
XII. Summary & Further Reading
Top 3 Takeaways:
The history and distribution of the rash are paramount for diagnosis. The pattern tells you the cause.
Management hinges on identifying and removing the trigger. Treatment will fail without this.
Treat inflammation with appropriate-potency topical steroids and restore the skin barrier with liberal use of emollients.
Key Resources:
UpToDate: "Irritant contact dermatitis in adults" and "Allergic contact dermatitis in adults".
Amboss: "Contact Dermatitis".
