A 28-year-old woman with a 6-year history of bipolar II disorder (recurrent hypomanic episodes and major depressive episodes) is being evaluated for treatment optimization. She has been on lithium for 2 years. Which investigation is most appropriate to assess long-term safety and guide ongoing therapy?

Question

Accepted Answer

C. Serum lithium level, renal function (creatinine, eGFR), and thyroid function tests. ## Long-Term Monitoring in Bipolar II Disorder on Lithium

**Key Point:** Lithium is a narrow-therapeutic-window drug with significant organ toxicity potential. Regular monitoring of serum levels, renal function, and thyroid function is mandatory for safe long-term use.

### Lithium Monitoring Protocol

**High-Yield:** The classic triad of lithium monitoring:

| Parameter | Frequency | Target Range | Clinical Significance |
|-----------|-----------|---------------|----------------------|
| Serum lithium level | Baseline, 5 days after initiation, then every 3–6 months | 0.6–1.2 mEq/L (therapeutic); >1.5 = toxicity | Narrow window; toxicity risk with dehydration, NSAIDs, ACE inhibitors |
| Renal function (creatinine, eGFR) | Baseline, 6 months, then annually | eGFR >60 mL/min/1.73m² | Lithium nephrotoxicity; chronic use → polyuric nephrogenic DI |
| Thyroid function (TSH, free T4) | Baseline, 6 months, then annually | TSH 0.5–5 mIU/L | Lithium-induced hypothyroidism in 20–30% of patients |

**Clinical Pearl:** In India, where iodine deficiency is endemic, lithium-induced hypothyroidism is particularly common. Baseline and annual thyroid screening is essential.

### Why Other Investigations Are Not Indicated

```mermaid
flowchart TD
  A[Bipolar II on Lithium ≥2 years]:::outcome
  A --> B{Routine monitoring needed?}:::decision
  B -->|Yes| C[Serum Li level + Renal + Thyroid]:::action
  C --> D{Any abnormality?}:::decision
  D -->|Elevated Li level| E[Adjust dose or frequency]:::action
  D -->|eGFR decline| F[Consider alternative mood stabilizer]:::action
  D -->|TSH elevation| G[Add levothyroxine or switch agent]:::action
  D -->|Normal| H[Continue lithium, repeat in 3-6 months]:::action
  B -->|PET/Genetic/PSG?| I[Not indicated for routine monitoring]:::urgent
```

**Mnemonic:** **LITHIUM MONITORING = SLEET**
- **S** = Serum level (0.6–1.2 mEq/L)
- **L** = Lithium toxicity signs (tremor, confusion, ataxia)
- **E** = Electrolytes & renal function (creatinine, eGFR)
- **E** = Endocrine (TSH, free T4)
- **T** = Timing (baseline, 5 days, then 3–6 monthly)

**Warning:** Do not confuse bipolar II (hypomania + depression) with bipolar I (mania + depression). Both require the same lithium monitoring, but bipolar II has shorter hypomanic episodes (<4 days) and often more depressive burden.

Answer

A. Genetic testing for bipolar susceptibility loci

Answer

B. Positron emission tomography (PET) brain scan

Answer

D. Polysomnography to assess sleep architecture

Explanation

Long-Term Monitoring in Bipolar II Disorder on Lithium

Lithium Monitoring Protocol

Why Other Investigations Are Not Indicated

Practice similar questions

Join our NEET PG community

Parameter	Frequency	Target Range	Clinical Significance
Serum lithium level	Baseline, 5 days after initiation, then every 3–6 months	0.6–1.2 mEq/L (therapeutic); >1.5 = toxicity	Narrow window; toxicity risk with dehydration, NSAIDs, ACE inhibitors
Renal function (creatinine, eGFR)	Baseline, 6 months, then annually	eGFR >60 mL/min/1.73m²	Lithium nephrotoxicity; chronic use → polyuric nephrogenic DI
Thyroid function (TSH, free T4)	Baseline, 6 months, then annually	TSH 0.5–5 mIU/L	Lithium-induced hypothyroidism in 20–30% of patients