How can I identify and treat a rash?

Identifying and Treating a Rash: A Systematic Approach

To identify a rash, first categorize it by morphology (petechial/purpuric, erythematous, maculopapular, or vesiculobullous), then assess for fever and systemic illness, as this algorithmic approach ensures life-threatening conditions are not missed. 1

Initial Assessment: Morphologic Classification

The first critical step is visual and tactile examination to categorize the rash into one of four patterns 1:

• Petechial/purpuric rashes: Non-blanching, pinpoint to larger purple lesions 1
• Erythematous rashes: Red, blanching lesions 1
• Maculopapular rashes: Flat or raised lesions with varied distribution 1
• Vesiculobullous rashes: Fluid-filled blisters or bullae 1

Critical Historical Features to Obtain

Focus your history on these specific high-yield elements 2:

• Timing: When did the rash start relative to fever onset? 3
• Medication exposure: Any new drugs in the past month, including over-the-counter medications, vitamins, or injections 4
• Environmental exposures: Recent travel, tick bites, animal contact, forest exposure 3, 2
• Distribution pattern: Does it involve palms/soles, face, sun-exposed areas, or flexor/extensor surfaces? 2
• Associated symptoms: Fever, pruritus, pain, systemic illness 1, 2

Red Flags Requiring Urgent Evaluation

Never dismiss a petechial rash without thorough evaluation, as meningococcemia requires urgent treatment. 5

Life-Threatening Petechial/Purpuric Rashes

• Meningococcemia: Rapid progression from maculopapular to petechial with deteriorating clinical condition, elevated WBC with left shift, markedly elevated inflammatory markers 5
• Rocky Mountain Spotted Fever (RMSF): Begins as small blanching pink macules on ankles/wrists/forearms 2-4 days after fever onset, progressing to maculopapular then petechial by day 5-6; classic triad of fever, rash, and tick bite present in only a minority initially 6
  • Incubation period: 3-12 days after tick bite 6
  • Palms and soles involvement occurs late and indicates advanced disease 6
  • Case-fatality rate: 5-10% 6

Distinguishing Viral from Bacterial Causes

• Viral petechial rashes (enteroviruses, coxsackievirus, echovirus): More generalized distribution, less likely to involve palms/soles, slower progression 5
• Bacterial causes: Rapid progression, deteriorating clinical status, abnormal laboratory findings 5

Treatment Approach by Rash Type

For Drug-Induced Rashes

If medication-related rash is suspected 4:

• Immediately discontinue the suspected agent 4
• Avoid rechallenging with drugs causing urticarial, bullous, or erythema multiforme-like eruptions, as this can be very dangerous 4
• Document all suspected agents for future avoidance 4

For Pruritic Inflammatory Rashes

Hydrocortisone cream 1-2.5% applied to affected areas 3-4 times daily is FDA-approved for temporary relief of itching from minor skin irritations, inflammation, eczema, psoriasis, poison ivy/oak/sumac, insect bites, and contact dermatitis. 7

For adults and children ≥2 years 7:

• Clean affected area with mild soap and warm water, rinse thoroughly, gently dry 7
• Apply hydrocortisone not more than 3-4 times daily 7
• For children <2 years: consult a physician 7

For Generalized Pruritus Without Visible Dermatosis

Emollients and self-care advice should be provided to all patients with generalized pruritus of unknown origin. 6

Basic management 6:

• Apply alcohol-free moisturizers at least twice daily, preferably urea-containing (5-10%) 6
• Avoid frequent washing with hot water 6
• Avoid skin irritants including over-the-counter anti-acne medications, solvents, disinfectants 6

For specific underlying causes 6:

• Iron deficiency: Iron replacement (Strength of recommendation C) 6
• Uraemic pruritus: Broadband UVB is effective (Strength of recommendation A); avoid long-term sedative antihistamines except in palliative care (Strength of recommendation B) 6
• Hepatic pruritus: Rifampicin as first-line (Strength of recommendation A), cholestyramine as second-line 6

When to Refer

Refer to dermatology if 8, 2:

• Diagnosis remains unclear after initial evaluation and the rash is not responding to empiric treatment 8
• Chronic grade 2 or higher rash develops that affects quality of life 6
• Suspected drug reaction with severe features (bullous, urticarial, erythema multiforme-like) 4
• Systemic symptoms suggest serious underlying disease requiring specialist evaluation 6

Common Pitfalls to Avoid

• Do not wait for the classic triad (fever, rash, tick bite) before considering RMSF, as it is present in only a minority at initial presentation 6
• Do not assume absence of rash rules out RMSF: <50% have rash in first 3 days, and some never develop rash 6
• Do not use sedative antihistamines long-term in uraemic pruritus, as they may predispose to dementia 6
• Do not use gabapentin for hepatic pruritus 6
• Do not overlook skin pigmentation that may make rashes difficult to recognize 6