When is lumbar puncture indicated in evaluation of patients with dementia?

A 84 yo female with PMH of CAD s/p stents (on ASA/Plavix), CVA, hypothyroidism, is admitted to the hospital with change in mental status (lethargy) and poor memory for 1 year. She is found to have hyponatremia of 120 mEq/L due to SIADH but no focal signs of infection. MRI/CT scans are unremarkable. EEG shows diffuse encephalopathy. CXR and UA are normal. She is placed on free water restriction and BMP is monitored q 12 hr.

Should a lumbar puncture be done for evaluation of her suspected dementia?

No.

Lumbar puncture (LP) is not needed in the evaluation of most patients with dementia. Some indications for LP in patients with dementia are listed below:
  1. Acute or subacute onset ( less than 8 weeks)
  2. Evidence of immunosuppression
  3. Fever or presence of meningeal signs
  4. Atypical presentation of dementia (e.g., severe headaches, seizures, cranial neuropathies)
  5. Symptoms of normal-pressure hydrocephalus (NPH)
  6. Positive serum fluorescent treponemal antibody absorption test
  7. Abnormalities on CT/MRI brain (e.g., meningeal enhancement)
In conclusion, LP and CSF analysis should not be part of the routine evaluation of patients with dementia and should probably be performed only in the presence of such indications as a subacute duration of dementia (less than 8 weeks), fever, and signs of meningeal irritation.

References:
Initial evaluation of suspected dementia: Asking the right questions. David C. Steffens, MD; Joel C. Morgenlander, MD. Postgrad Med, 1999.
The role of lumbar puncture in the evaluation of dementia: the Durham Veterans Administration/Duke University Study. Becker PM, Feussner JR, Mulrow CD, Williams BC, Vokaty KA. J Am Geriatr Soc. 1985 Jun;33(6):392-6.
Image source: Wikipedia, GNU Free Documentation License.

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