A 28-year-old woman is brought to the emergency department with severe abdominal pain, profuse watery diarrhea, and hypotension after consuming contaminated well water. Her 45-year-old father, occupationally exposed to arsenic dust for 15 years, presents with progressive sensorimotor peripheral neuropathy and skin pigmentation changes. Which finding most reliably distinguishes the father's chronic arsenic neuropathy from the daughter's acute arsenic toxicity?

Explanation

## Arsenic Neuropathy: Chronic vs Acute Presentation ### Neurological Manifestations by Exposure Type **Key Point:** Chronic arsenic exposure causes a characteristic sensorimotor peripheral neuropathy with axonal degeneration (length-dependent, distal-to-proximal), whereas acute arsenic poisoning may cause encephalopathy or acute neuropathy but does not develop the chronic axonal pattern seen in occupational exposure. ### Comparative Neuropathology | Feature | Chronic Arsenic Neuropathy | Acute Arsenic Toxicity | |---------|---------------------------|------------------------| | **Pattern** | Sensorimotor, length-dependent | Encephalopathy, acute GI-dominant | | **Nerve conduction finding** | Axonal degeneration (reduced CMAP/SNAP) | Normal or non-specific changes | | **Onset** | Insidious (months to years) | Acute (hours) | | **Distribution** | Distal lower limbs first (stocking-glove) | Diffuse or absent in acute phase | | **Fiber involvement** | Both motor and sensory fibers | Not prominent in acute poisoning | | **Reversibility** | Partially reversible; residual deficits common | May recover if patient survives acute phase | | **Associated findings** | Skin changes, Mees' lines, GI symptoms mild | Severe GI hemorrhage, shock, no skin changes | ### Why Axonal Degeneration Pattern is the Best Discriminator 1. **Temporal signature:** Axonal degeneration develops only after cumulative, prolonged exposure (weeks to months). 2. **Electrophysiological specificity:** Nerve conduction studies show reduced compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes with relatively preserved conduction velocities — classic axonal pattern. 3. **Absent in acute poisoning:** Acute arsenic toxicity presents with encephalopathy and GI collapse; peripheral neuropathy does not have time to develop an axonal pattern. 4. **Length-dependent distribution:** The distal-to-proximal, stocking-glove pattern is pathognomonic for chronic occupational exposure. **High-Yield:** Chronic arsenic neuropathy is **sensorimotor** (both motor and sensory), **axonal** (not demyelinating), and **length-dependent** — these three features together distinguish it from acute toxicity. ### Clinical Pearl **Mnemonic: ASHEN** — Arsenic neuropathy features: - **Axonal** degeneration pattern - **Sensorimotor** involvement - **Hyperkeratosis** and skin changes (concurrent) - **Exposure** history (occupational, chronic) - **Neuropathy** is length-dependent, distal-predominant ### Acute Arsenic Toxicity: Neurological Manifestations When acute arsenic poisoning affects the nervous system, it presents as: - Encephalopathy (confusion, altered mental status) - Seizures (in severe cases) - Peripheral neuropathy is **not** a feature of acute poisoning The daughter's acute presentation will show GI and cardiovascular collapse, not peripheral neuropathy.