Psychopharmacology — MCQs

Question 361: What is the most appropriate investigation for a patient with bipolar disorder on lithium therapy for 6 months, who presents with seizures, coarse tremors, confusion, and weakness of the limbs after a day of fasting?

• A. Serum Electrolyte
• B. ECG
• C. Serum Lithium (Correct Answer)
• D. Serum creatinine

Explanation: ***Serum Lithium*** - The patient's symptoms (seizures, coarse tremors, confusion, weakness) are classic signs of **lithium toxicity**. - Fasting can lead to **dehydration** and electrolyte imbalances, which can increase lithium levels and precipitate toxicity. *Serum Electrolyte* - While electrolyte imbalances can contribute to lithium toxicity and symptoms, measuring electrolytes alone will not directly confirm **lithium overdose**. - **Hyponatremia** and **dehydration** can exacerbate lithium toxicity by increasing renal reabsorption of lithium. *ECG* - **ECG changes** (e.g., T-wave abnormalities, QTc prolongation) can occur with severe lithium toxicity, but it is not the primary diagnostic test. - ECG is a supportive investigation to assess cardiac complications, not the direct cause of the neurological symptoms. *Serum creatinine* - **Serum creatinine** is important for monitoring **renal function**, as lithium is cleared renally and renal impairment can lead to higher lithium levels. - However, assessing creatinine levels will not directly diagnose acute lithium toxicity; it helps evaluate the **renal health** and potential for toxicity.