What is the appropriate diagnosis and treatment for a facial rash in a patient of unknown age with an unspecified medical history?

Approach to Facial Rash: Diagnostic and Treatment Algorithm

Immediate Diagnostic Priorities

The first step is to determine if this is a life-threatening condition requiring immediate intervention, followed by systematic evaluation based on age, morphology, and associated symptoms. 1, 2

Critical Red Flags Requiring Emergency Action

• If multiple uniform "punched-out" erosions or vesiculopustular eruptions are present, immediately initiate systemic acyclovir plus empirical antibiotics to cover eczema herpeticum 1
• If extensive crusting, weeping, or honey-colored discharge is present, this indicates severe bacterial superinfection requiring flucloxacillin for Staphylococcus aureus coverage 1
• If the patient presents with a red swollen face, consider potentially life-threatening conditions including angioedema, severe drug reactions (particularly DRESS syndrome), necrotizing fasciitis, or dermatomyositis 3

Age-Specific Diagnostic Approach

Children Under 4 Years

Atopic dermatitis is the primary consideration when facial involvement occurs in children under 4 years, as it characteristically affects the cheeks or forehead in this age group 1

Essential diagnostic criteria include:

• An itchy skin condition PLUS three or more of: history of itchiness in skin creases or cheeks, personal or family history of atopy, general dry skin in the past year, visible flexural eczema or facial involvement, and onset in the first two years of life 1

Adults and Older Patients

For adults, the differential diagnosis is broader and requires assessment of:

• Symptomology, age of onset, rash morphology, and specific clinical clues 4
• Many common diagnoses can be made clinically without investigations 4

Specific Diagnostic Considerations

Scabies (Any Age, Particularly Institutional Settings)

Consider scabies in any patient with an unexplained generalized rash, particularly in long-term care facility residents 5, 2

• Diagnosis requires light microscopy demonstration of mites, eggs, or mite feces on mineral oil preparations of multiple skin scrapings 5, 2
• Proper technique requires vigorous scraping of 20 papules to maximize diagnostic yield 2
• In debilitated patients, presentation may be atypical with absence of burrows, inflammatory changes in intertriginous areas, and only hyperkeratosis, papules, or vesicles 2
• If proper diagnostic equipment is unavailable or clinical experience is limited, consult a dermatologist 5, 2

Drug-Induced Rash

Record all medicines taken and vaccinations received over the preceding 2 months, including over-the-counter and complementary/alternative therapies 5

• Document the date treatments were initiated, dose escalations, when drugs were stopped, and any brand switches or medication errors 5
• The ALDEN (ALgorithm of Drug causality in Epidermal Necrolysis) online tool can predict likely causality of a drug reaction 5
• Immediately discontinue any potential culprit drug 5

Infectious Etiologies

Investigate potential infectious aetiology in all patients 5

For herpes simplex or herpes zoster:

• Skin scrapings may be examined for giant cells (Tzanck preparation) and/or sent for culture, immunofluorescent viral antigen studies, or PCR 5
• Herpes zoster presents as painful vesicular rash in dermatomal distribution 2

For bacterial infections:

• Surface swab cultures are indicated for conjunctivitis but not for most other bacterial skin infections 5
• Needle aspiration or deep-tissue biopsy may be appropriate when unusual pathogens are suspected, fluctuant areas suggest abscess, or initial antimicrobial treatment has been unsuccessful 5

First-Line Treatment Algorithm

For Atopic Dermatitis in Children

Apply emollients liberally and frequently, at least twice daily, to all affected areas and ideally after bathing 1

• Use a dispersible cream as a soap substitute instead of regular soaps and detergents, as they remove natural lipids and worsen dry skin 1
• Apply topical corticosteroids as the mainstay of treatment, selecting the least potent preparation required to control the eczema 1
• Use very potent and potent categories for limited periods only to avoid pituitary-adrenal suppression 1
• Do not abruptly discontinue high-potency corticosteroids without transition to appropriate alternative treatment, as this can cause rebound flare 1

Environmental and Trigger Management

• Keep nails short to minimize damage from scratching 1
• Avoid irritant clothing such as wool next to the skin and avoid extremes of temperature 1
• Maintain cool environmental temperature to prevent heat-related exacerbation 6

Treatment of Secondary Bacterial Infection

Use flucloxacillin for S. aureus (most common pathogen), phenoxymethylpenicillin if β-hemolytic streptococci isolated, and erythromycin for penicillin allergy or flucloxacillin resistance 1

Critical Pitfalls to Avoid

• Do not overuse potent topical steroids, which can cause pituitary-adrenal suppression and growth interference in children 1
• Do not prescribe non-sedating antihistamines, which have little to no value in atopic eczema; use sedating antihistamines only for severe pruritus during relapses, particularly at night 1
• Do not restrict diet without professional supervision, as dietary manipulation is rarely beneficial and can cause nutritional deficiencies 6
• Do not make a clinical diagnosis of scabies alone in institutional settings without microscopic confirmation, as this can lead to pseudo-outbreaks with widespread "psychogenic" scabies 2
• Do not confuse benign skin conditions with conditions requiring urgent intervention such as eczema herpeticum or Stevens-Johnson syndrome 6

When to Obtain Investigations

Skin biopsy is useful if:

• The diagnosis is unclear 4
• The rash is not responding to initial treatment 4
• A referral to a dermatologist is being considered 4

Follow-Up and Patient Education

Allow adequate time for explanation and discussion with parents, as education regarding application of topical preparations and quantity to use is essential 1

• Demonstrate how to apply treatments and provide written information to reinforce the issues discussed 1
• Reassess in 1-2 weeks if no improvement occurs with initial therapy, as failure to improve requires urgent evaluation for alternative diagnoses or complications 1