A 52-year-old woman with bipolar I disorder has been stable on lithium 900 mg daily (serum level 0.8 mEq/L) for 3 years. She now presents with polyuria, polydipsia, and a urine osmolality of 180 mOsm/kg. All of the following are recognized adverse effects of chronic lithium therapy EXCEPT:

Explanation

## Chronic Lithium Adverse Effects **Key Point:** Lithium causes **nephrogenic diabetes insipidus (NDI)**, **hypothyroidism**, and **hyperparathyroidism** as chronic dose-dependent effects. However, acute tubular necrosis (ATN) is NOT a recognized adverse effect of lithium therapy. ### Lithium-Induced Endocrine and Renal Complications | Adverse Effect | Mechanism | Onset | Clinical Features | |---|---|---|---| | **Nephrogenic DI** | Damage to aquaporin-2 channels in collecting duct; impaired ADH response | Months to years | Polyuria, polydipsia, low urine osmolality (<200 mOsm/kg) | | **Hypothyroidism** | Inhibition of thyroid peroxidase; ↓ iodine uptake; ↑ TSH | 6–12 months | Fatigue, weight gain, cold intolerance; ↑ TSH, ↓ free T~4~ | | **Hyperparathyroidism** | Shift in PTH set point for Ca^2+^ suppression (rightward shift) | Months to years | Hypercalcaemia, ↑ PTH, nephrolithiasis, bone loss | | **Chronic kidney disease** | Interstitial fibrosis and tubular atrophy (gradual) | Years | Progressive ↑ creatinine, proteinuria | **High-Yield:** The patient's presentation of **polyuria + polydipsia + low urine osmolality** is pathognomonic for **lithium-induced nephrogenic DI**. This is a dose-dependent, partially reversible effect. ### Why Acute Tubular Necrosis Is NOT a Lithium Effect **Clinical Pearl:** Lithium does **not** cause acute tubular necrosis (ATN). ATN is an acute, severe kidney injury characterized by: - Sudden rise in serum creatinine (hours to days) - Muddy brown casts in urine - Oliguria or anuria - Causes: sepsis, rhabdomyolysis, nephrotoxins (contrast, aminoglycosides, cisplatin) Lithium causes **chronic, insidious renal damage** (interstitial fibrosis, NDI) over months to years, not acute tubular injury. Acute lithium toxicity presents with **neurotoxicity** (tremor, confusion, seizures, coma), not ATN. ### Mnemonic for Lithium Chronic Toxicity **THINE** — **T**hyroid, **H**yperparathyroidism, **I**nsipidus (nephrogenic DI), **N**ephropathy (chronic), **E**ndocrine effects ### Management of Lithium-Induced NDI 1. **Amiloride** (potassium-sparing diuretic) — blocks lithium entry into collecting duct cells via ENaC channels; first-line treatment 2. **NSAIDs** — reduce urine output (use cautiously; ↑ lithium levels) 3. **Low-sodium diet** — enhances proximal tubule reabsorption of lithium and water 4. **Adequate hydration** — prevents dehydration and lithium toxicity 5. **Consider lithium discontinuation** if severe and refractory **Warning:** Do NOT confuse lithium-induced NDI with central DI (ADH deficiency). NDI is **ADH-resistant**; desmopressin will NOT help. ## Summary The **incorrect statement** is acute tubular necrosis. Lithium causes chronic renal damage (NDI, interstitial fibrosis) and endocrine complications (hypothyroidism, hyperparathyroidism), but NOT acute ATN.