Learning Objectives
Differentiate between bacterial and viral skin infections based on the depth of tissue involvement and specific clinical signs. Master the diagnostic markers for Staphylococcal Scalded Skin Syndrome (SSSS) vs. Toxic Epidermal Necrolysis (TEN), and identify the unique presentations of Herpes and Molluscum Contagiosum.
1. Bacterial Skin Infections (Pyoderma)
| Infection |
Skin Depth & Pathogen |
Clinical Hallmark |
| Impetigo |
Superficial epidermis (S. aureus / S. pyogenes). |
Honey-colored crusting; highly contagious. |
| Erysipelas |
Upper dermis + lymphatics (S. pyogenes). |
Well-defined, raised demarcation from normal skin. |
| Cellulitis |
Deep dermis + subcutaneous tissue. |
Spreading, painful erythema with poorly defined borders. |
| Necrotizing Fasciitis |
Deep tissue/fascia (Anaerobes / S. pyogenes). |
Pain out of proportion to exam; crepitus (gas); surgical emergency. |
2. Toxin-Mediated & Deep Bacterial Lesions
| Condition |
Mechanism / Target |
Key Clinical Signs |
| SSSS |
Exotoxin destroys the stratum granulosum only. |
(+) Nikolsky sign; No mucosal involvement; heals completely. |
| Abscess |
Collection of pus in deeper layers (S. aureus). |
Walled-off, fluctuant, and painful nodule. |
3. Viral Skin Infections
| Virus |
Condition |
Clinical Features |
| HSV-1 / HSV-2 |
Herpes (Labialis, Genitalis, Whitlow). |
Vesicles on an erythematous base; painful. |
| Poxvirus |
Molluscum Contagiosum |
Umbilicated papules (central dimple). |
| VZV |
Varicella (Chickenpox) / Zoster (Shingles). |
Dermatomal reactivation (Zoster) or multi-stage crops (Varicella). |
| EBV |
Hairy Leukoplakia |
White, unscrapable lateral tongue plaques (HIV). |
Activity:
High-Yield Mnemonics & Tips:
- SSSS vs. TEN: SSSS is Superficial (stratum granulosum). TEN is a Total epidermal destruction.
- Hairy Leukoplakia: Think “Unscrapable”. If you can scrape it off, it’s Thrush (Candida).
- Molluscum: The central dimple looks like a “belly button” (Umbilicated).
Activity:
