Lithium toxicity with normal blood level

[Cknight]

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What are the possible causes?
Thanks.

 

[Doc Samson]

Lab error

 

[daru1]

Ect 😛

 

[Cknight]

Hmm.. thanks for the input. My attending asked me this today, stating there is a classic cause, yet I didn't find anything clearly stated, and was just wondering if I'm missing something blatant.

 

[billypilgrim37]

Getting more obscure, this could certainly happen following chronic overdose, as lithium doesn't cross the blood-brain barrier. The serum level could drop to zero, but the level in the CSF would be much higher and could be associated w/ toxicity. But that's not really snappy enough for your attending's question.

 

[Encephalopathy]

Agree with daru, I think your attending is looking for ECT.

 

[Cknight]

That must be it then; thanks a lot for your help guys.👍

 

[masterofmonkeys]

electrolyte abnormalities could potentially do it as well. Sodium, calcium, and magnesium specifically IIRC.

 

[whopper]

Lab values being "normal" are based on population studies. As we should know from statistics, there will always be outliers that may be within normal limits, but don't get normal results.

Some people could fall within a normal range for lithium and still get toxicity. It will be rare, but it could happen, especially if the lithium is on the higher side of the therapeutic range.

Now why that happens, on a level better explanable by the statistical explanation-that would be the more interesting answer.

 

[BabyPsychDoc]

There is no good correlation between Li serum levels and clinical symptoms of Li toxicity. This is a widely reported phenomenon - patients can (and do) get symptoms of Li toxicity (particularly, the neurological sx) with their Li serum levels in normal range. Nobody really knows why, but both whopper and BP37 put forward theories that have been suggested as possible explanations to the phenomenon.

Another possible explanation is that your patient is taking a medication that increases CNS sensitivity to Li. SSRIs are the most common offenders in this group.

 

[Cknight]

Well, I asked her today, and she was thinking about the discrepancy between the CSF and blood levels (how the latter can normalize but there can be very high doses in the CSF). I guess the context is overdose. I truly did not understand why this happens (billypilgrim37 touched upon this), but I guess that's what she was referring to.

 

[daru1]

Wow, sorry about not responding. I wasn't joking around, and had every plan to come back and explain the blood-brain barrier reason for ect causing that (thank you bp). Inpatient is really busy these days.