CSF: How certain can we be?

Meira Louis

PGY1

Objectives

• Present a published case highlighting the difficulties in CSF diagnosis

• Understand the objective evidence for the tests ordered on CSF

• Understand where clinical judgement falls in the spectrum of certainty

Sheila21yo female

1 day history:– non-specific lethargy– Fever and rigors– Generalized headache– Nausea, vomiting

PMX:– Childhood asthma– Hyperthyroidism

Meds:– None

Huynh et al, 2007

• On exam:– Vitals: 38°C– Alert, oriented– Normal neuro

• Bloodwork– WBC: 19.5– CRP: 185– Lytes, LFTs,

glucose

• Imaging:– Chest X-ray– Urinalysis– CT head

CSF – for what?

• Cell count• Gram’s Stain• Turbidity• Xanthochromia• Glucose• Protein• India Ink• Cryptococcal Antigen• Lactic Acid• Bacterial Antigen tests• Acid Fast Stain

Sheila’s CSF

• Clear and colourless

• Protein: 0.38 mg/dL

• Glucose: 3.6 mmol/L

• 12x106 RBC

• 1x106 WBC (all mononuclear)

• Negative gram stain

What would you do?

• What’s your diagnosis?

• How confident are you?

• How confident should you be?

Cell Count and Differential

• How many leuks are too many leuks?

• Does it matter what kind?– Monomorphic vs polymorphic– lymphocytosis

• Does prior abx change your cell count?

Thomson et al, 2001.; Van de Beek, 2004.

What happens with a traumatic tap?

Predicted WBC = CSF RBC x serum WBC

serum RBC

• If WBC was more than 10x normal was 48% predictive of bacterial meningitis

• If less than 10x was 99% predictive of it NOT being meningitis

Mayefsky et al. 1987

Glucose

• Hypoglycorrhachia

• If normal serum glucose:– Ratio of CSF:serum is 0.6:1– Abnormal when less than 0.5

• If elevated serum glucose:– Ratio of CSF:serum is 0.4:1– Abnormal when less than 0.3

Protein

• Normal range in CSF: 15-45 mg/dL– Greater than 150 is probably bacterial– Greater than 1000 should suggest fungal

• Other causes?– Any meningitis– Subarachnoids– CNS vasculitis– Syphilis– Viral encephalitis– neoplasms

Gram Stain

All common etiologies-no previous antibiotics 75-90%All common etiologies-antimicrobial therapy prior to LP 40-60%Streptococcus pneumoniae 90%Neisseria meningitidis 75%Haemophilus influenzae 86%Listeria monocytogenes <50%Gram-negative bacilli 50%

What’s the sensitivity for bacteria?

Gray et al, 1992

Other tests

Lactic Acid• Non-specific• Elevations over 35 mg/dL may indicate

bacterial meningitis• Lactate may rise before glucose dropsSerum Procalcitonin• Very sensitive • Not available for up to 24 hours

Back to the case…

• The following morning:– Diplopia, worsening headache– Temp increase to 40°C– GCS of 9– No rash, no nuchal rigidity, no focal neuro

• Repeat CT scan with contrast• IV ceftriaxone, gentamicin, and acyclovir were

started• Blood and CSF came back positive for N.

meningitidis

On a reassuring note…

Sensitivity Specificity Accuracy

ER doc 0.89 0.77 0.79

CSF leuk 0.50 0.94 0.71

Glucose 0.33 0.42 0.11

Protein 0.63 0.94 0.75

CRP 0.78 0.74 0.75

Procalcitonin 0.87 1.00 0.99

Ray et al, 2006