A 42-year-old man is admitted to the burns unit 4 hours after contact with a hot cooking vessel. He has a 15 cm × 10 cm area on his right forearm that is charred black, leathery, and painless. The edges show a zone of erythema with blistering. On examination, there is no blanching when pressure is applied to the charred area, and a needle prick produces no response in the affected zone. The surrounding erythematous area shows brisk blanching and pain on touch. What is the depth of the primary burn injury in the charred central zone?

Explanation

## Full-Thickness (Third-Degree) Burn Diagnosis **Key Point:** Full-thickness burns are defined by complete destruction of the epidermis and dermis, with loss of all sensory and vascular function in the affected zone. ### Clinical Features in This Case The charred central zone demonstrates: - **Charred, leathery appearance** — indicates coagulation necrosis of all skin layers - **Painlessness** — nerve endings are destroyed - **Absence of blanching** — no viable capillaries; microcirculation is obliterated - **No response to needle prick** — complete loss of sensory innervation - **Black or white discoloration** — tissue necrosis These findings are **diagnostic of full-thickness (third-degree) burn**. ### Burn Depth Comparison: Partial vs. Full-Thickness | Feature | Superficial Partial (2°) | Deep Partial (2°) | Full-Thickness (3°) | | --- | --- | --- | --- | | **Appearance** | Erythematous, blistered | Pale, mottled, leathery | Charred, white, or brown | | **Pain** | Severe | Reduced/dull | Absent (painless) | | **Blanching** | Brisk, immediate | Sluggish | Absent | | **Sensation** | Intact | Reduced | Absent | | **Hair removal** | Singed, removable | Easily removed | Firmly adherent or burnt | | **Healing** | Spontaneous (7–21 days) | Prolonged (>3 weeks) | Requires grafting | | **Scarring** | Minimal | Significant | Severe, contractures | **High-Yield:** The **absence of pain and blanching** is the most reliable bedside sign of full-thickness burns and distinguishes them from partial-thickness injury. ### Zones of Burn Injury (Jackson's Theory) ```mermaid flowchart TD A[Burn Injury]:::outcome --> B[Zone of Coagulation<br/>Central - Full thickness]:::urgent A --> C[Zone of Stasis<br/>Middle - Partial thickness]:::action A --> D[Zone of Hyperemia<br/>Peripheral - Erythema only]:::outcome B --> E[Irreversible damage<br/>Requires grafting] C --> F[Potentially salvageable<br/>With fluid resuscitation] D --> G[Recovers spontaneously] ``` **Clinical Pearl:** In this case, the **charred central zone** represents the zone of coagulation (full-thickness), while the **erythematous periphery with blistering** represents the zone of stasis (partial-thickness). The zone of stasis can progress to full-thickness if inadequately resuscitated. **Mnemonic: "CNS" (Full-Thickness Burns)** — **C**harred appearance, **N**o pain, **S**ensation absent. ### Why the Surrounding Erythema Is Different The erythematous zone with blistering at the periphery shows: - Brisk blanching → viable circulation - Pain on touch → intact nerves - Blistering → dermal-epidermal separation This is **superficial partial-thickness (second-degree)** and represents the zone of stasis, which may be salvaged with aggressive fluid resuscitation. **Management Note:** Full-thickness burns require early surgical debridement and skin grafting. Escharotomy may be needed if circumferential burns compromise circulation. [cite:Park 26e Ch 18]