A 42-year-old man is brought to the emergency department with acute poisoning. He presents with severe vomiting, abdominal pain, and bloody diarrhea. Laboratory investigations show elevated liver enzymes and acute kidney injury. Which is the most common organ system affected in acute arsenic poisoning?

Explanation

## Most Common Organ System Affected in Acute Arsenic Poisoning **Key Point:** The gastrointestinal tract is the MOST COMMON and FIRST organ system affected in acute arsenic poisoning, regardless of the route of exposure. ### Pathophysiology of Arsenic Toxicity ```mermaid flowchart TD A[Arsenic Exposure]:::outcome --> B[Trivalent As III binds SH groups]:::action B --> C[Inhibits cellular enzymes]:::action C --> D{Which organ first?}:::decision D -->|Acute ingestion| E[GI tract - direct corrosive effect]:::urgent D -->|Acute inhalation| F[GI tract - swallowed + absorbed]:::urgent E --> G[Vomiting, diarrhea, abdominal pain]:::outcome F --> G G --> H[Fluid loss + electrolyte imbalance]:::outcome H --> I[Hypovolemic shock]:::urgent I --> J[Multi-organ failure]:::urgent ``` ### Timeline of Organ Involvement in Acute Arsenic Poisoning | Timeframe | Primary Organ | Secondary Organs | Clinical Features | |-----------|---------------|------------------|------------------| | **0–6 hours** | **GI tract** | — | Nausea, vomiting, abdominal pain, diarrhea | | **6–24 hours** | GI tract + Cardiovascular | Heart, blood vessels | Hypotension, arrhythmias, shock | | **24–72 hours** | Multi-organ | Liver, kidneys, CNS | Hepatotoxicity, AKI, encephalopathy | | **>72 hours** | Chronic effects | Peripheral nerves, skin | Peripheral neuropathy, hyperkeratosis | ### Why GI Tract Is Most Commonly Affected 1. **Direct corrosive effect** — Arsenic trioxide and arsenite salts are caustic to mucous membranes 2. **First point of contact** — Whether ingested or inhaled (swallowed), arsenic reaches the GI tract early 3. **Rapid absorption** — GI epithelium absorbs arsenic quickly, leading to systemic effects 4. **High incidence** — GI symptoms occur in >90% of acute arsenic poisoning cases **Clinical Pearl:** The triad of acute arsenic poisoning is **vomiting + abdominal pain + bloody diarrhea** ("rice-water" or hemorrhagic diarrhea). This is the hallmark presentation and occurs within hours of exposure. **High-Yield:** Arsenic binds to sulfhydryl (-SH) groups in proteins, inhibiting pyruvate dehydrogenase and other critical enzymes. This causes cellular energy depletion and multi-organ dysfunction, but the GI tract is affected FIRST because of direct contact and high metabolic activity of enterocytes. **Mnemonic:** **ACHE** — Arsenic causes: - **A**bdominal pain - **C**ardiovascular collapse (later) - **H**yperkeratosis (chronic) - **E**ncephalopathy (late) But the **first** and **most common** system is GI. ### Why Other Systems Are Secondary - **Cardiovascular:** Affected in acute poisoning but AFTER GI symptoms (6–24 hours); hypotension is due to fluid loss from GI bleeding and vomiting - **CNS:** Encephalopathy is a late manifestation (>24 hours) and less common than GI involvement - **Respiratory:** Not a primary target organ in acute poisoning; respiratory distress occurs secondary to pulmonary edema or aspiration