Which of the following is the earliest clinical sign of lithium toxicity?

Explanation

## Early Signs of Lithium Toxicity **Key Point:** The earliest and most common manifestation of lithium toxicity is a **fine tremor** accompanied by **gastrointestinal symptoms** (nausea, vomiting, diarrhea). ### Stages of Lithium Toxicity | Severity | Serum Level | Early Signs | Intermediate Signs | Severe Signs | | --- | --- | --- | --- | --- | | **Mild** | 1.5–2.0 mEq/L | Fine tremor, GI upset, polyuria | Coarse tremor, confusion, diarrhea | — | | **Moderate** | 2.0–3.5 mEq/L | Coarse tremor, nausea, vomiting | Ataxia, slurred speech, nystagmus | Hyperreflexia, muscle rigidity | | **Severe** | > 3.5 mEq/L | Seizures, coma, cardiac arrhythmias | Renal failure, pulmonary edema | Death | **High-Yield:** Fine tremor is a **dose-dependent side effect** that may persist even at therapeutic levels; it is NOT necessarily a sign of toxicity. However, when accompanied by GI symptoms (nausea, vomiting, diarrhea) at higher serum levels, it signals early toxicity. **Clinical Pearl:** Gastrointestinal symptoms (nausea, vomiting, diarrhea) are often the **first warning sign** that serum lithium is rising into the toxic range. Patients should be counseled to report these symptoms immediately. **Mnemonic: TREMOR-GI** — **T**remor (fine, then coarse), **R**estlessness, **E**xcitability, **M**uscle weakness, **O**scillations (nystagmus later), **R**igidity (late) + **G**astrointestinal upset (early marker).