11.3 Bipolar Disorder, Mood Stabilizers & Lithium Toxicity
Key Takeaways
- Bipolar I requires a manic episode, while bipolar II requires hypomania with a major depressive episode and no history of mania.
- Lithium toxicity is precipitated by volume depletion, non-steroidal anti-inflammatory drugs, thiazides and angiotensin-converting enzyme inhibitors.
- Severe lithium toxicity with neurologic impairment or kidney failure is treated with hemodialysis.
- Lithium causes nephrogenic diabetes insipidus, chronic tubulointerstitial disease and hypothyroidism, requiring periodic monitoring.
- Valproate is contraindicated in people who may become pregnant because of neural tube defects and adverse neurodevelopmental outcomes.
1. Bipolar Disorder: Classification, Mood Stabilizers & Lithium Toxicity
Bipolar disorder is characterized by pathological fluctuations in mood, energy, and activity levels. Accurate differentiation from unipolar depression is critical, as incorrect pharmacotherapy can trigger life-threatening mania.
Diagnostic Distinction: Bipolar I vs. Bipolar II vs. Cyclothymia
| Diagnostic Category | Diagnostic Criteria & Episode Characteristics | Psychosis & Hospitalization | Functional Impairment |
|---|---|---|---|
| Bipolar I Disorder | >=1 Lifetime Manic Episode (major depressive episode is common but not required for diagnosis). Manic episode: Distinct period of abnormally and persistently elevated, expansive, or irritable mood + increased goal-directed activity lasting >= 1 week (or any duration if hospitalization is necessary), with >=3 DIG FAST symptoms (>=4 if mood is irritable) | Psychotic features (delusions, hallucinations) may be present; frequently requires emergent hospitalization | Severe impairment in social, occupational, or interpersonal functioning |
| Bipolar II Disorder | >=1 Hypomanic Episode AND >=1 Major Depressive Episode; must NEVER have had a full manic episode. Hypomanic episode: Lasts >= 4 consecutive days with >=3 DIG FAST symptoms; clear change from baseline observable by others | NO psychotic features; does NOT require hospitalization | Unequivocal change in functioning, but does NOT cause severe social or occupational impairment |
| Cyclothymic Disorder | Chronic, fluctuating mood disturbance lasting >= 2 years in adults (>=1 year in adolescents) with numerous periods of hypomanic symptoms and depressive symptoms that do not meet full criteria for hypomania or major depression | No psychosis; no hospitalization | Mild-to-moderate chronic distress and functional impairment |
DSM-5 Manic Symptom Mnemonic: "DIG FAST"
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D — Distractibility (attention easily drawn to unimportant external stimuli)
I — Indiscretion / Impulsivity (excessive involvement in high-risk activities: spending sprees, sexual indiscretions, reckless driving)
G — Grandiosity (inflated self-esteem, delusions of special power, wealth, or identity)
F — Flight of ideas (subjective experience that thoughts are racing; rapid topic shifting)
A — Activity increase (increased goal-directed activity socially, at work, or sexually) or psychomotor agitation
S — Sleep decreased need (feels fully rested and energized after only 2 to 3 hours of sleep)
T — Talkativeness (pressured, rapid, loud speech that is difficult or impossible to interrupt)
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CRITICAL ABIM BOARD SAFETY RULE: Antidepressant Monotherapy in Bipolar Disorder Initiating antidepressant monotherapy (SSRIs, SNRIs, TCAs, Bupropion) in a patient with Bipolar I or Bipolar II disorder is strictly contraindicated. Antidepressant monotherapy carries a high risk of precipitating an acute switch into mania or hypomania, triggering mixed states, or accelerating rapid cycling (>4 mood episodes/year). In bipolar depression, mood stabilizers or approved atypical antipsychotics must always be used as first-line therapy.
First-Line Mood Stabilizer Pharmacology & Monitoring
1. Lithium Carbonate
- Mechanism of Action: Alters transmembrane cation transport; inhibits inositol monophosphatase (depleting neuronal second-messenger PIP2); inhibits Glycogen Synthase Kinase-3 (GSK-3beta); promotes neurogenesis and neuroprotection.
- Efficacy: Gold-standard mood stabilizer for acute mania, bipolar maintenance, and bipolar depression; proven to reduce suicide mortality and completed suicide rates by >5-fold in bipolar and recurrent unipolar depression.
- Therapeutic Serum Levels (12-hour trough level):
- Acute Mania: 0.8 to 1.2 mEq/L
- Long-Term Maintenance: 0.6 to 0.8 mEq/L (elderly: 0.4 to 0.6 mEq/L)
- Mandatory Baseline & Routine Monitoring:
- Renal Function (BUN, Serum Creatinine, eGFR): Lithium is 100% cleared by the kidneys; monitor every 3-6 months.
- Thyroid Function (TSH, Free T4): Lithium inhibits thyroid hormone synthesis and release (causes benign goiter and hypothyroidism in 15-20% of patients; manage by adding Levothyroxine, do not discontinue lithium).
- Serum Calcium: Lithium alters calcium-sensing receptors, causing hyperparathyroidism and hypercalcemia; monitor annually.
- Urinalysis: Screen for Nephrogenic Diabetes Insipidus (NDI) (polyuria, polydipsia, low urine osmolality <300 mOsm/kg despite water deprivation; lithium enters principal cells via ENaC channels and disrupts aquaporin-2 expression; treated with Amiloride which blocks ENaC, plus thiazides/indomethacin).
- Baseline 12-Lead ECG: T-wave flattening, sinus node dysfunction.
- Pregnancy Test (beta-hCG): First-trimester exposure carries an elevated risk of Ebstein Anomaly (apical displacement of the tricuspid valve leaflets, atrialization of the right ventricle, tricuspid regurgitation; absolute risk ~1 in 1000 live births vs 1 in 20,000 baseline).
Lithium Toxicity Clinical Manifestations & Hemodialysis Triggers
| Toxicity Severity & Serum Level | Clinical Signs & Neurological Manifestations | Precipitating Factors & Drug-Drug Interactions | Management Protocol |
|---|---|---|---|
| Mild-to-Moderate Toxicity<br/>(1.5 to 2.0 mEq/L) | Coarse hand tremor, muscular weakness, ataxia, dysarthria, sluggishness, lethargy, persistent nausea, vomiting, watery diarrhea | Dehydration, volume depletion, fever, reduced oral fluid intake, low-sodium diets | Discontinue lithium; obtain stat serum lithium level, CMP, and ECG; administer IV 0.9% Normal Saline at 150-200 mL/h to restore GFR |
| Moderate-to-Severe Toxicity<br/>(2.0 to 2.5 mEq/L) | Coarse tremor, profound ataxia, hyperreflexia, muscle fasciculations, myoclonus, confusion, delirium, visual hallucinations, flat affect | Drug Interactions that Impair Renal Lithium Excretion:<br/>1. NSAIDs (ibuprofen, naproxen, celecoxib; reduce renal prostaglandin synthesis -> decrease renal blood flow and GFR)<br/>2. ACE Inhibitors & ARBs (lisinopril, losartan; decrease GFR)<br/>3. Thiazide Diuretics (hydrochlorothiazide, chlorthalidone; promote sodium loss in distal tubule -> compensatory proximal reabsorption of Na and Li)<br/>(Note: Aspirin and Sulindac have minimal effect on lithium levels) | ICU admission; aggressive IV 0.9% Normal Saline volume resuscitation; continuous telemetry; avoid forced diuresis with loop diuretics |
| Severe Life-Threatening Toxicity<br/>(> 2.5 mEq/L or > 4.0 mEq/L) | Seizures, status epilepticus, non-convulsive status, generalized hypertonia, stupor, coma, ventricular arrhythmias, circulatory collapse, acute oliguric renal failure, death | Severe acute overdose, acute-on-chronic ingestion, severe renal failure | EMERGENT HEMODIALYSIS INDICATIONS:<br/>1. Serum Lithium Level > 4.0 mEq/L regardless of clinical symptoms.<br/>2. Serum Lithium Level > 2.5 mEq/L in the presence of severe neurological toxicity (seizures, coma, marked delirium) or acute renal failure.<br/>3. Hemodynamically unstable patient or lithium levels continuing to rise despite IV saline hydration. (Note: Continue HD until level is <1.0 mEq/L; monitor for post-dialysis rebound release from intracellular stores) |
A 46-year-old woman with Bipolar I disorder maintained on Lithium Carbonate 600 mg BID (with a stable baseline serum level of 0.8 mEq/L) presents to the emergency department with severe nausea, persistent vomiting, coarse bilateral hand tremors, unsteady gait, slurred speech, and progressive confusion over the past 2 days. Her family reports that 5 days ago, she developed acute right knee pain from osteoarthritis and began taking over-the-counter high-dose ibuprofen (800 mg three times daily). On physical examination, temperature is 36.8°C (98.2°F), blood pressure is 108/68 mmHg, heart rate is 62 bpm, and dry mucous membranes are noted. Neurological examination reveals marked bilateral horizontal nystagmus, dysmetria on finger-to-nose testing, generalized hyperreflexia (3+ patellar reflexes), and wide-based ataxia. Laboratory testing reveals: BUN 38 mg/dL, Serum Creatinine 2.2 mg/dL (baseline 0.9 mg/dL), Serum Sodium 138 mEq/L, Serum Potassium 4.1 mEq/L, and Serum Lithium level 2.8 mEq/L. Which of the following is the most appropriate management strategy?