A 38-year-old woman with bipolar I disorder has been stable on lithium 900 mg daily for 2 years. She now presents with polyuria, polydipsia, and a serum sodium of 138 mEq/L. All of the following are recognized adverse effects of chronic lithium therapy EXCEPT:

Explanation

## Chronic Lithium Adverse Effects: Clinical Recognition and Mechanisms ### Lithium's Organ-Specific Toxicity Profile **Key Point:** Lithium causes multiple organ-system adverse effects through distinct mechanisms. Chronic use is associated with renal, thyroid, and neurological complications — but NOT hyperkalemia. In fact, lithium may cause hypokalemia or normokalemia. ### Adverse Effects of Chronic Lithium Therapy | Organ System | Adverse Effect | Mechanism | Clinical Presentation | |--------------|---|---|---| | **Renal** | Nephrogenic diabetes insipidus (NDI) | Downregulation of aquaporin-2 channels in collecting duct; resistance to ADH | Polyuria, polydipsia, hypernatremia | | **Thyroid** | Hypothyroidism (most common) | Inhibition of thyroid peroxidase; reduced iodine uptake | Fatigue, weight gain, cold intolerance, elevated TSH | | **Neurological** | Fine tremor, hyperreflexia | Increased intracellular Na^+^ and Ca^2+^; altered neurotransmitter function | Early signs; may progress to toxicity | | **Cardiac** | Arrhythmias, ST-T wave changes | Lithium competes with K^+^ intracellularly; alters cardiac conduction | Flattened T waves (NOT peaked T waves) | | **Renal** | Chronic interstitial nephritis | Direct tubular toxicity; fibrosis with long-term use | Progressive renal impairment | ### Why Option 3 Is Incorrect **High-Yield:** Lithium does NOT cause hyperkalemia. Instead: - Lithium competes with K^+^ for intracellular entry and renal reabsorption - Chronic lithium use may cause **hypokalemia** or **normokalemia** - Cardiac effects (flattened T waves, arrhythmias) occur due to altered cardiac conduction, NOT hyperkalemia - Peaked T waves (characteristic of hyperkalemia) are NOT a lithium effect **Clinical Pearl:** The patient in this vignette has classic signs of lithium-induced nephrogenic diabetes insipidus (polyuria, polydipsia, elevated serum sodium 138 mEq/L). This is one of the most common chronic adverse effects, affecting 20–40% of patients on long-term lithium. ### Management of Chronic Lithium Adverse Effects **Key Point:** Chronic adverse effects often require: 1. **NDI:** Amiloride (potassium-sparing diuretic) to block lithium entry into collecting duct cells 2. **Hypothyroidism:** Levothyroxine replacement if TSH elevated 3. **Renal impairment:** Monitor serum creatinine; consider alternative mood stabilizer if eGFR < 30 4. **Tremor:** Beta-blockers (propranolol) if bothersome **Mnemonic: LITHIUM CHRONIC TOXINS** — **L**ow thyroid, **I**ncreased urine output, **T**remor, **H**ypernatremia, **I**nterstitial nephritis, **U**nchanged K^+^ (NOT elevated), **M**onitoring essential.