NBME 23 Decreased CSF production by the choroid plexus (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 3/Question#39 (reveal difficulty score)
A 44-year-old woman comes to the physician ...
Decreased CSF production by the choroid plexus 🔍 / 📺 / 🌳 / 📖
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submitted by ∗hayayah(1212)

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Carbonic anhydrase inhibitors (eg, acetazolamide) and loop diuretics (eg, furosemide) are thought to exert their effect on ICP by reducing cerebrospinal fluid (CSF) production at the choroid plexus.

Google says mechanism is unknown LOL.

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usmleuser007 Just FYI: Mannitol can also be used to reduce ICP by drawing free water out of CNS Howeveer, it can cause hypernatremia, pulmonary edema, and expansion of ECV can exacerbate heart failure +4

jimdooder I think a good way to remember this is that CA inhibitors have very similar effects in the eye (reducing production of aqueous humor) as they do in the ventricles (decrease production of CSF). Can't say I totally understand the mechanisms but thats the connection I made. +5

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submitted by ∗uslme123(86)

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This question makes no sense to me. She has an extremely low opening pressure yet has signs of increased intracranial pressure. Did they mean to put 32 cm H20?????????

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uslme123 Standard lab values are incorrect, way to go NBME. +3

wutuwantbruv I think they mean to put mm Hg. Normal CSF pressure is about 100-180 mm H20 which equates to about 8-15 mm Hg. +4

alexb I lost a bit of time wondering about that ugh lol +1

mjmejora I thought there must be an obstruction in the ventricles somewhere preventing csf from getting to the spine. so pressure is low in spinal tap but in the head it must be really high. +2

donttrustmyanswers Does anyone have clarification on this question? +

llamastep1 Pseudo tumor cerebri can have normal ICP. Who knew +1

tyrionwill Hi, mjmejora, MRI did not see anything abnormality, couldn't this mean that there was no obstruction in the ventricles? +1

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submitted by motherfucker(6)

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MedScape: "Acetazolamide (ACZ) and furosemide (FUR) treat posthemorrhagic hydrocephalus in neonates. Both are diuretics that also appear to decrease secretion of CSF at the level of the choroid plexus."

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submitted by ∗usmile1(154)

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In patients with IIH treated with acetazolamide, the inhibition of carbonic anhydrase in the choroid plexus results in a reduction of CSF production and flow. The acid–base status of the patient may also alter the distribution of acetazolamide in the CSF and brain, but its effect on the CSF flow is secondary to that mediated by the choroid plexus. Based on the pharmacology and distribution of acetazolamide and carbonic anhydrase in the brain, the theory that emphasizes the effect of acetazolamide on CSF production in IIH is most likely primary and direct, and weight loss, when recognized as a factor, is secondary and indirect, and frequently the result of toxic doses in excess of the amount needed for complete enzyme inhibition.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4315016/

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submitted by ∗handsome(3)

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fa 2020 pg 527 You'll see IDIOPATHIC INTRACRANIAL HYPERTENSION

Also called pseudotumor cerebri. INCREASE ICP with no obvious findings on imaging. Risk factors include female sex, Tetracyclines, Obesity, vitamin A excess, Danazol (female TOAD).

Treatment: weight loss, acetazolamide, invasive procedures for refractory cases (eg, CSF shunt placement, optic nerve sheath fenestration surgery for visual loss

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medb FA 2020 pg 521** under idiopathic intracranial hypertension +

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submitted by ∗whoissaad(102)

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HCO3- is needed to make CSF. Acetazolamide inhibits carbonic anhydrase and decrease HCO3- absorption from renal tubules.

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mario could be pseudo tumor cereberi, ttt is also acetazolamide and is more common in female obese BMI 35KG/M +

mario opening pressure could be normal in pseudo tumor cereberi +

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