Question:medium
A person on treatment with lithium for a mood disorder presents with seizures, increased reflexes, and epileptic fits. The patient also has a history of severe gastroenteritis. On investigation, the serum lithium level was found to be 1.95 mEq/L. This patient is most likely suffering from
A person on treatment with lithium for a mood disorder presents with seizures, increased reflexes, and epileptic fits. The patient also has a history of severe gastroenteritis. On investigation, the serum lithium level was found to be 1.95 mEq/L. This patient is most likely suffering from
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Lithium level above about 1.5 mEq/L, plus dehydration from gastroenteritis reducing renal clearance, plus seizures and hyperreflexia, means toxicity.
Updated On: Jul 8, 2026
- Severe dehydration
- Lithium toxicity
- Epilepsy
- Manic episode
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
This question tests whether you can connect a drug level, a triggering illness, and a set of neurological signs into one diagnosis.
Step 2: Key Approach:
First check the lithium number against the known safe range, then look for a reason the level rose, then match the symptoms to that cause.
Step 3: Detailed Explanation:
The normal therapeutic window for lithium is roughly 0.6 to 1.2 mEq per litre. A reading of 1.95 mEq per litre is clearly past the toxic cutoff of about 1.5 mEq per litre.
Why did the level rise even though the patient was on a stable dose before? The severe gastroenteritis caused vomiting and diarrhoea, which dehydrated the patient and lowered the glomerular filtration rate. Since lithium is cleared almost entirely by the kidney and behaves much like sodium, less filtration means less lithium leaves the body, so it piles up in the blood.
The seizures and increased reflexes are textbook central nervous system findings of lithium toxicity, which happens because lithium at high concentration disturbs neuron excitability.
Dehydration by itself is the mechanism that caused the toxicity, but naming dehydration as the final diagnosis misses the actual poisoning that is now driving the seizures. Epilepsy would need a seizure disorder that exists apart from any drug, which the history does not support. A manic episode changes mood and energy, it does not raise a lithium level or cause fits.
Step 4: Final Answer:
Putting the toxic drug level together with the dehydration trigger and the neurological signs, the diagnosis is lithium toxicity.
This question tests whether you can connect a drug level, a triggering illness, and a set of neurological signs into one diagnosis.
Step 2: Key Approach:
First check the lithium number against the known safe range, then look for a reason the level rose, then match the symptoms to that cause.
Step 3: Detailed Explanation:
The normal therapeutic window for lithium is roughly 0.6 to 1.2 mEq per litre. A reading of 1.95 mEq per litre is clearly past the toxic cutoff of about 1.5 mEq per litre.
Why did the level rise even though the patient was on a stable dose before? The severe gastroenteritis caused vomiting and diarrhoea, which dehydrated the patient and lowered the glomerular filtration rate. Since lithium is cleared almost entirely by the kidney and behaves much like sodium, less filtration means less lithium leaves the body, so it piles up in the blood.
The seizures and increased reflexes are textbook central nervous system findings of lithium toxicity, which happens because lithium at high concentration disturbs neuron excitability.
Dehydration by itself is the mechanism that caused the toxicity, but naming dehydration as the final diagnosis misses the actual poisoning that is now driving the seizures. Epilepsy would need a seizure disorder that exists apart from any drug, which the history does not support. A manic episode changes mood and energy, it does not raise a lithium level or cause fits.
Step 4: Final Answer:
Putting the toxic drug level together with the dehydration trigger and the neurological signs, the diagnosis is lithium toxicity.
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