Lumbar puncture

Contraindications

1. Infection at LP site
2. Severe thrombocytopenia (platelets <50) or bleeding diathesis or INR >1.5
3. Mass lesion suspected (do CT or MRI first)

CT Head before LP

• If any of the following:

1. AMS
2. Focal Neurologic deficit
3. Papilledema
4. Head Trauma or h/o CNS disease (recent or remote)
5. New Onset Sz (<1 wk prior to ED visit)
6. HIV + / AIDS or any immunocompromised (transplant pt, steroids, cancer) patient
7. Age > 60.
8. VP shunt

CT findings that prohibit LP

1. Midline shift
   1. Look for unequal pressures between the 3 cerebral compartments (left/right supretentorial compartments, posterior fossa)
   2. Look for intracerebral masses not causing midline shift
2. Obsutrictive hydrocephalus
   1. Look for enlargement of ventricles prox to lesions and normal ventricles distal (especially 4th ventricle)
3. Basilar cisterns compressed
   1. Look for lateral/3rd ventricles may be small due to diffuse cerebral edema or enlarged due to obstr. hydroceph. +/- shift
4. Posterior fossa mass
   1. Look for displacement/compression of 4th ventricle

Normal Values

Parameter	Preterm Infant	Term Neonate	Child
Celll Count (WBC)	9 (0-25) >30 suggests meningitis	8 (0-22) >30 suggests meningitis	0-7, >10 in child >1mo suggests meningitis
PMN (%)	57	61	0
Glucose	52 (24-63)	52 (34-119)	40-80
Protein	115 (65-150)	90 (20-170)	5-40
RBC	0	0	0

Subarachnoid Hemorrhage vs Bloody Tap

1. Xanthrochromia: suggestive of hemorrhage
2. RBC <50 suggestive of bloody tap
3. 50-600 = gray zone)
4. >600 c/w SAH
5. Incr opening pressure c/w SAH

Meningitis

Bacterial

1. Appearance Cloudy or purulent
2. Glucose (mg/dl) <40 or <40% serum
3. Protein (mg/dl) >100-500
4. Cell Count 100-100,000 (>5)
5. Differential >80% PMN
6. Pressure (cm H2O) Usually Inc

Fungal

1. Appearance Clear or cloudy
2. Glucose (mg/dl) 20-40
3. Protein (mg/dl) 25-500
4. Cell Count 25-1000
5. Differential mono & lymph
6. Pressure (cm H2O) N or I
7. India ink 50% sensitivity
8. LA assay for crypto antigen 80%.

Aseptic/Viral

1. Appearance Clear
2. Glucose (mg/dl) N or D
3. Protein (mg/dl) 50-200
4. Cell Count WBC 10-100
5. Differential Inc mono & PMN early, then lymph.
6. Pressure (cm H2O) N or I

TB

1. Appearance Cloudy
2. Glucose (mg/dl) <40
3. Protein (mg/dl) 100-2000
4. Cell Count 50-500
5. Differential Most lymph, some PMN
6. Pressure (cm H2O) Usually Incr

HSV

1. Appearance Bloody or xantho
2. Glucose (mg/dl) N or D
3. Protein (mg/dl) 50-100
4. Cell Count 20-500
5. Differential Mostly lymph
6. Pressure (cm H2O) N or Incr

Neoplasm

1. Appearance Clear or xantho
2. Glucose (mg/dl) 40-80
3. Protein (mg/dl) 50-1000
4. Cell Count <100
5. Differential Mostly lymph
6. Pressure (cm H2O) Usually Incr

Guillain-Barre

1. Appearance Clear or cloudy
2. Glucose (mg/dl) Normal
3. Protein (mg/dl) slight Inc
4. Cell Count <100
5. Differential Mostly lymph
6. Pressure (cm H2O) Normal

Source

Emergency Radiology: Case Studies Schwartz

Hasbun, R. et al, (Yale), NEJM, Dec 13, 2001. (prospective, 301 pts)