## Chronic Arsenic Poisoning: Cutaneous Manifestations **Key Point:** Mees' lines (horizontal white transverse bands on the nails) are the pathognomonic cutaneous finding in chronic arsenic poisoning. ### Mechanism of Mees' Lines Mees' lines develop due to: 1. Arsenic binding to sulfhydryl groups in keratin of the nail matrix 2. Disruption of normal nail pigmentation and keratinization 3. Appearance as horizontal white bands separated by normal nail color 4. Typically appear 2–3 months after chronic exposure 5. Gradually grow out with the nail (can be used for forensic dating) ### Other Cutaneous Features of Chronic Arsenic Poisoning | Feature | Timing | Mechanism | |---------|--------|----------| | Hyperkeratosis (palms/soles) | Months to years | Chronic irritation, arsenic accumulation | | Hyperpigmentation | Months to years | Melanin deposition, irritant dermatitis | | Bowen's disease | Years | Premalignant transformation | | Squamous cell carcinoma | Years to decades | Arsenic is a Group 1 carcinogen | | Mees' lines | 2–3 months | Keratin-arsenic binding in nail matrix | **High-Yield:** Mees' lines are NOT specific to arsenic alone—they can also occur in thallium, bismuth, and severe systemic illness (renal failure, chemotherapy). However, in the context of heavy metal poisoning, arsenic is the classic association. **Clinical Pearl:** The presence of Mees' lines in a patient with unexplained peripheral neuropathy, GI symptoms, or skin lesions should raise suspicion for arsenic poisoning and prompt toxicology screening. **Mnemonic:** **MEES** = **M**etal poisoning (arsenic), **E**xposed nails, **E**vidence of chronic toxicity, **S**ulfhydryl binding. ### Why Not the Other Options? - **Raynaud's phenomenon:** Associated with chronic arsenic exposure but is NOT pathognomonic (seen in connective tissue diseases, occupational exposure to vinyl chloride). - **Erythema multiforme:** Can occur with arsenic but is not characteristic or pathognomonic. - **Pemphigus vulgaris:** Autoimmune blistering disorder unrelated to arsenic toxicity.
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