Signs of Lithium Toxicity
Lithium toxicity presents with a spectrum of clinical manifestations that progress with increasing serum levels, beginning with gastrointestinal and neuromuscular symptoms at lower levels and advancing to severe neurological dysfunction at higher concentrations.
Early Signs (Serum Levels <2 mEq/L)
The initial manifestations of lithium toxicity can occur even at therapeutic or slightly supratherapeutic levels, particularly in sensitive patients:
- Gastrointestinal symptoms including diarrhea, nausea, and vomiting are often the earliest indicators of toxicity 1
- Neuromuscular signs such as drowsiness, muscular weakness, and lack of coordination appear early in the toxic process 1
- Fine hand tremor may be present and can persist throughout treatment, though this may also occur as a benign side effect 1
- Patients should be educated to recognize these early warning signs to facilitate prompt intervention 2
Moderate Toxicity (Serum Levels 2-3 mEq/L)
As lithium levels rise, more pronounced neurological symptoms emerge:
- Giddiness and ataxia become prominent features 1, 3
- Visual disturbances including blurred vision 1
- Tinnitus (ringing in the ears) 1
- Polyuria with large output of dilute urine 1
- Confusion and altered mental status ranging from impaired attention to delirium 4, 5
- Slurred speech and dysarthria 1
Severe Toxicity (Serum Levels >3 mEq/L)
At levels exceeding 3 mEq/L, a complex multi-organ clinical picture develops:
- Severe neurological dysfunction including stupor, coma, and seizures 1, 5
- Movement disorders such as choreo-athetotic movements, muscle fasciculations, twitching, and clonic movements of limbs 1
- Hyperactive deep tendon reflexes and muscle hyperirritability 1
- Cardiovascular manifestations including cardiac arrhythmias, hypotension, severe bradycardia from sinus node dysfunction (potentially causing syncope), and peripheral circulatory collapse 1, 6
- Incontinence of urine or feces 1
- Acute dystonia and downbeat nystagmus 1
Additional Clinical Manifestations
Beyond level-dependent toxicity, several other signs may occur:
- Headache, nausea, sweating, and dizziness can indicate serotonergic syndrome when lithium is combined with certain medications 7
- Vertigo with associated nausea and vomiting 1
- Blackout spells and psychomotor retardation 1
- Dehydration and lethargy 1
Critical Pitfalls
- Toxicity can occur at levels below 1.5 mEq/L in sensitive patients, so clinical presentation takes precedence over absolute serum levels 1
- Mental status and neurological symptoms often predominate, making the diagnosis potentially elusive due to slow onset and diverse manifestations 4
- Hydration status is crucial in assessing toxicity risk, as volume depletion from lithium-induced nephrogenic diabetes insipidus commonly precipitates chronic poisoning 8, 5
- Chronic poisoning is the most common pattern and is usually unintentional, resulting from lithium intake exceeding elimination 5