A 35-year-old farmer from Punjab presents with progressive peripheral neuropathy, skin hyperpigmentation, and Mees' lines on the nails. His colleague, exposed to the same occupational hazard but presenting with acute gastroenteritis, rice-water stools, and cardiovascular collapse, is suspected of acute poisoning. Which clinical feature best distinguishes chronic arsenic toxicity from acute arsenic poisoning?

Explanation

## Distinguishing Chronic vs Acute Arsenic Poisoning ### Clinical Presentation Timeline **Key Point:** Mees' lines (horizontal white lines on nails) and chronic skin changes (hyperpigmentation, hyperkeratosis, Bowen's disease) are pathognomonic features of chronic arsenic exposure and take weeks to months to develop, making them the best discriminator between chronic and acute toxicity. ### Comparative Features | Feature | Chronic Arsenic Toxicity | Acute Arsenic Poisoning | |---------|--------------------------|------------------------| | **Onset** | Insidious (weeks to months) | Rapid (minutes to hours) | | **Mees' lines** | Present (appears after 4-6 weeks) | Absent in acute phase | | **Skin changes** | Hyperpigmentation, hyperkeratosis, Bowen's disease | Absent | | **GI symptoms** | Mild, intermittent | Severe: hemorrhagic gastroenteritis, rice-water stools | | **Cardiovascular** | Peripheral vascular disease, Raynaud's | Acute shock, arrhythmias | | **Neurological** | Peripheral neuropathy (sensorimotor) | Encephalopathy, seizures (if severe) | | **Mortality** | Chronic (malignancy risk) | Acute (within 24–72 hours if untreated) | ### Why Mees' Lines Are the Best Discriminator 1. **Temporal specificity:** Appear only after 4–6 weeks of exposure; absent in acute poisoning. 2. **Pathognomonic appearance:** Horizontal white transverse bands on nails are virtually diagnostic of chronic arsenic exposure. 3. **Persistent finding:** Remain visible for months even after exposure cessation, reflecting cumulative dose. 4. **Not seen in acute poisoning:** Acute arsenic toxicity presents with fulminant GI and cardiovascular collapse before nail changes can develop. **High-Yield:** Mees' lines move distally with nail growth and eventually disappear; their presence confirms chronic exposure, not acute poisoning. ### Clinical Pearl Other chronic arsenic skin findings include: - **Hyperpigmentation** (diffuse or raindrop pattern) - **Hyperkeratosis** (palms and soles) - **Bowen's disease** (squamous cell carcinoma in situ) - **Arsenic keratosis** (wart-like lesions) These all require prolonged exposure and are absent in acute toxicity.