Meningitis
The brain and spinal cord are surrounded by three membranes, which, from the outside inwards, are the dura mater, the arachnoid mater and the pia mater. Between the arachnoid mater and the pia mater, in the subarachnoid space, is found the cerebrospinal fluid (CSF).This fluid is secreted by the choroid plexuses and vascular structures which are in the third, fourth and lateral ventricles. CSF passes from the ventricles via communicating apertures to the subarachnoid space, after which it flows over the surface of the brain and the spinal cord.
Acute bacterial meningitis
- mostly due to hematogenous dissemination.- Most common causes are:
during the first 2 months of life: group B & D streptococcus, G-ve enteric bacilli, L. momocytogenes, H. influenza (occasionally).
from 2 months to 12 yr age: S.pneumonia, N. meningitides, H. influenza type b.
- the mode of transmission is person to person contact through respiratory tract secretions or droplets.
Clinical features:
Non specific signs and symptoms: fever, anorexia, poor feeding, symptoms of URTI, tachycardia, Hypotension.
Signs of increase intracranial pressure: bulging fontanel, headache, emesis, cranial nerve paralysis, Hypertension with bradycardia, apnea or hyperventilation, coma. Papilloedema is uncommon.
Signs of Meningeal irritation neck rigidity (more if the posterior meningies of the brain are involved), Kernig's sign (flexing the hip to 90 defree & extend the knee pain & limitation of knee extension), Brudzinski's sign (wn pt neck is passively flexed while supine involuntary flexion of the hips).
Babinski's response: plantar response (extension) stretching & disruption of the corticospinal fibers originating from the leg region of the motor cortex. It is normal up to 1 yr of age because myelination is incomplete.
- causes of sterile bulging fontanel:
1. drugs ex. Tetracycline, vit. C, vit. A&D tox, steroid, nalidixic acid, Erythromycine, ampicilline.
2. idiopathic
Rx:
1- antibiotics immediately
The antimicrobial therapy of meningitis requires attainment of adequate levels of bactericidal agents within the CSF. The passage of antibiotics into CSF is dependent on:
1) degree of meningeal inflammation
2) integrity of blood–brain barrier created by capillary endothelial cells.
3) properties of the antibiotic:
• lipid solubility (the choroidal epithelium is highly impermeable to lipid-insoluble molecules)
• ionic dissociation at blood pH
• protein binding
• molecular size
• concentration of the drug in the serum.
- choice of Rx in im.competent infants & children:
50% of S.pneumonia are resistant to penicillin
25% = = = to cefotaxime & ceftriaxone.
Based on substantial rate of resistance of S.pneumonia to β-lactam drugs, recommended antibiotic Rx is for 10-14 days with:
Vancomycin i.v (60 mg/kg/day ÷4) + 3rd gener cephalosporine i.v (either cefotaxime 200 mg/kg/day ÷4 or ceftriaxone 100 mg/kg/day).
Patient allergic to β-lactam antibiotics can be treated w` chloramphenicol i.v 100 mg/kg/day ÷4
Most strains of N. meningitidis are sensitive to penicilline & cephalos. Duration of Rx is 5-7 days
40% of H.influenza-b produce β-lactamase and resist penicillin but these strains remain sensitive to cephalosp. Duration of Rx is 7-10 days.
If L.monocytogenes (ex. in infant 1-2 months old or T-lymphocyte deficiency), treatment should be with ampicilline 200 mg/kg/day ÷4 + ceftraixone or cefotaxime
- in im.compromised pt (suspected G-ve bact) ceftazidime + aminoglycoside
- S.E of Ab Rx:
Phlebitis, drug fever, rash, emesis, oral candidiasis, diarrhea.
Ceftriaxone reversible gallbladder pseudolithiasis which emesis & right upper quadrant pain.
2- steroids:
- indications for steroids: ↑ICP, cerebral edema, shock, T.B, H.infl.
Dexamethasone 0.15 mg/kg/dose ×4 for 2 days for child > 6wk of age with H.infl-b meningitis.
But the use of steroids is controversial for other bacterial meningitis.
steroids have maximum benefit if given 1-2 hr before Ab were initiated.
Complications of steroid are mentioned in previous lecture.
3- i.v fluid
Fluid should be restricted to 1/2 – 2/3 of maintenance until it can be established that ↑ICP or syndrome of inappropriate antidiuretic hormone secretion (SIADH) is not present. But the Shock must be Rx aggressively.
Septic shock also require vasoactive agents ex. Dopamine, epinephrine & Na-nitroprusside.
4- Signs of ↑ICP s.b Rx emergently with endotracheal intubation & hyperventilation, i.v furosemide (1 mg/kg), mannitol (1 g/kg).
5- i.v diazepam for Rx of seizures, 0.1 mg/kg/dose (or lorazepam 0.05 mg/kg/dose)
After immediate management of seizures, pt should receive phenytoin (20 mg/kg loading, then 5 mg/kg/day maintenance).
Phenytoin is preferred to phenobarbiton because less CNS depression.
6-Supportive care:
s.glucose, Ca, Na should be monitored.
Viral meningoencephalitis
In viral meningoencephalitis, the CSF is characterised by pleocytosis & absence of microorganisms on Gram stain.
Rx:
With the exception of the use of acyclovir for HSV encephalitis, Rx is supportive.
Brain abscess
Rx:Start the Rx with the following until the culture result become available (Duration of Ab Rx usually 4-6 weeks):
1- if unknown pathogene 3rd gener cephalosp + metronidazole
2- if there is a history of head trauma or neurosurgery nafcillin or vancomycin + 3rd generation cephalosp + metronidazole
Alternative: meropenem (only)
3- if there is cyanotic heart disease penicillin + metronidazole
4- infected ventriculoperitoneal shunt vancomycin + ceftazidime
5- otitis media, sinusitis, or mastoiditis vancomycine + 3rd gener ceph + metronidazole
6- citrobacter meningitis (often in neonates) 3rd gener ceph + aminoglycoside
7- im.compromised amphotericin B
الدكتور
صلاح مهدي فرحاناختصاصي طب الاطفال والخدج
مستشفى الحسين (ع) التخصصي للأطفال