A 38-year-old woman is brought to the hospital with a 2-week history of progressive weakness, paresthesias in her hands and feet, and gastrointestinal disturbances. Her husband mentions she has been consuming homemade cosmetic creams purchased from an unlicensed vendor for the past 6 months to lighten her skin. On examination, she has hyperpigmentation on the face with a characteristic 'Mees' lines' on her fingernails, and peripheral neuropathy. Her blood arsenic level is 45 µg/dL (normal <10 µg/dL). What is the most likely diagnosis and the appropriate chelating agent?

Explanation

## Clinical Diagnosis: Chronic Arsenic Poisoning ### Key Clinical Features **High-Yield:** The classic triad of chronic arsenic poisoning is: 1. **Mees' lines** — horizontal white lines on the nails (pathognomonic finding) 2. **Peripheral neuropathy** — typically sensorimotor, affecting distal lower limbs first 3. **Hyperpigmentation** — diffuse or localized (especially on face, neck, trunk) **Key Point:** Mees' lines (also called Aldrich-Mees lines) are transverse white lines on the nails that appear 2–3 months after arsenic exposure and move distally as the nail grows. They are highly suggestive of arsenic toxicity but are NOT pathognomonic (can occur in other heavy metal poisonings, renal failure, or chemotherapy). ### Source Identification The patient's exposure to unlicensed cosmetic creams is a common source of chronic arsenic poisoning in India, particularly in skin-lightening products that may contain inorganic arsenic compounds. ## Chelation Therapy in Chronic vs. Acute Arsenic Poisoning | Feature | Acute Arsenic Poisoning | Chronic Arsenic Poisoning | |---------|------------------------|---------------------------| | **Onset** | Hours to days | Weeks to months | | **Presentation** | GI symptoms, shock, AKI | Neuropathy, skin changes, Mees' lines | | **Chelator of choice** | BAL (dimercaprol) | DMSA (succimer) | | **Timing** | Within 24 hrs of ingestion | Can be given at any time | | **Route** | IM (BAL) | Oral (DMSA) | | **Duration** | 2 days IM, then 1 week IM | 5 days per course; may repeat | | **Efficacy** | High in acute phase | Better for chronic exposure; less GI upset | **Mnemonic:** **BAL for Acute, DMSA for Chronic** — BAL (dimercaprol) is lipophilic and crosses the blood-brain barrier, making it ideal for acute toxicity with CNS involvement; DMSA (succimer) is water-soluble, oral, and better tolerated for chronic exposure. **Clinical Pearl:** DMSA (meso-2,3-dimercaptosuccinic acid) is the preferred agent for chronic arsenic poisoning because: - **Oral bioavailability** — easier to administer than IM BAL - **Better tissue penetration** — effective in chronic tissue accumulation - **Fewer side effects** — less GI upset and fewer systemic reactions compared to BAL - **Proven efficacy** — reduces urinary arsenic excretion and improves symptoms of chronic neuropathy ### Why NOT BAL in Chronic Poisoning? While BAL is highly effective in acute arsenic poisoning (within 24 hours), it is **not recommended for chronic poisoning** because: 1. It is administered IM, making long-term therapy impractical 2. It has a short half-life and requires frequent dosing 3. It causes more systemic side effects (hypertension, tachycardia, fever) 4. DMSA is superior for chronic tissue-bound arsenic ## Correct Answer Rationale The patient has **chronic arsenic poisoning** (evidenced by Mees' lines, peripheral neuropathy, hyperpigmentation, and chronic exposure history). The appropriate chelating agent is **DMSA (succimer)** at 10 mg/kg orally three times daily for 5 days, which can be repeated if necessary. This is the standard-of-care regimen for chronic arsenic toxicity.