🧪 How to Approach Skin Rash – Don’t Stop at the “Appearance”

by poohmedical
June 9, 2025

“I’ve got these bumps on my skin…”
“It’s so itchy I can’t sleep.”
“I’ve broken out in a rash and now I have a fever too.”

Skin problems are one of the most common chief complaints in clinical practice. However, the ability to observe skin lesions, describe them in words, and generate differential diagnoses tends to be overlooked. This article presents a structured approach to skin rashes, including the important concept of the “dermadrome”.

🧠 Why “Appearance-Only” Isn’t Enough

Skin findings can be signs of systemic diseases. Go beyond visual diagnosis by describing morphology, thinking in patterns, and considering systemic implications.

🔍 Clinical Steps for Skin Rash Evaluation

Step 1: Listen Carefully and Gather Background Information

• When did it start?
• How did it progress?
• Associated symptoms (fever, itch, pain)?
• New medications?
• Travel, contacts, animals?

Step 2: Describe the Lesion Precisely

📖 Dermatological Morphology – Standard Definitions

Term	Description
Macule	Flat, discolored spot (≤1 cm)
Papule	Small, raised, firm bump (≤1 cm)
Nodule	Larger, deeper lump (>1 cm)
Vesicle	Small, fluid-filled blister (≤1 cm)
Bulla	Large fluid-filled blister (>1 cm)
Pustule	Pus-filled lesion
Plaque	Broad, elevated lesion
Scale	Flaky or shedding surface
Crust	Dried serum or exudate (scab)
Erosion	Superficial skin loss without scarring
Ulcer	Deeper skin loss with potential scarring
Purpura	Non-blanchable red/purple spots
Lichenification	Thickened skin from chronic scratching

Step 3: Classify the Rash

• Distribution: Localized? Generalized? Dermatomal?
• Configuration: Linear? Annular? Target-like?
• Symmetry: Unilateral or bilateral?
• Surface features: Scaly? Crusted?

Step 4: Think “Dermadrome”

Skin reflects systemic disease. Examples:

• Grouped vesicles + dermatomal pattern: Herpes zoster
• Erythema multiforme + mucosal involvement: Stevens-Johnson Syndrome
• Non-blanching purpura + fever: Meningococcemia, Vasculitis
• Pruritic rash + eosinophilia: Drug eruption

💡 Clinical Application: Herpes Zoster

Case: 62-year-old man with pain and vesicular rash on one side of chest.

• Grouped vesicles on red base
• Follows a single dermatome
• Unilateral and doesn’t cross midline
• Burning pain

Also check for eye involvement, immunosuppression, and risk of post-herpetic neuralgia.

📍 Clinical Pearls

• Describe morphology, distribution, and evolution
• Always check drug history
• Use correct terminology
• Suspect systemic causes when rash is unusual or generalized

👤 Useful Medical English

Expression	Usage
Do you have any itchiness or pain?	Describing symptoms
Did the rash start suddenly or gradually?	Onset
Any new medications or supplements?	Drug screening
Has anyone around you had a similar rash?	Infection clue
Did it spread or stay in one area?	Distribution

📚 References

• Japanese Dermatology Clinical Guidelines 2023 – Herpes Zoster
• UpToDate: Herpes zoster – Clinical features and diagnosis
• NEJM: Herpes Zoster – Clinical Review, 2018
• Atarashii Hifukagaku, 4th edition (Hiroshi Shimizu)
• VisualDx (dermatology image database)

📘 Read in Japanese | 🌐 More symptom-based guides