Pyogenic meningitis in children

Overview

Pyogenic (bacterial) meningitis is inflammation of the membranes covering the brain and spinal cord (dura, arachnoid and pia) caused by bacteria. When the brain tissue is also inflamed the term is meningoencephalitis. It can kill within hours if untreated, accounts for about 3% of paediatric admissions, is commonest in infancy and is slightly more frequent in boys. Any febrile young infant without an obvious focus of infection should make you think of it.

Aetiology

Organisms by age

• Greatest risk is between 6 and 12 months; about 95% of cases occur between 1 month and 5 years.
• Staphylococcal meningitis follows neurosurgery, skull fracture or penetrating head injury.
• Otitis media and mastoiditis lead to pneumococcal or streptococcal meningitis.
• Nelson notes that routine Hib and pneumococcal vaccines have made these two much rarer where coverage is high.

Risk factors

• Immune deficiency, sickle cell disease, asplenia (functional or anatomical).
• Crowding (homes, day care, hostels).
• CSF leak after a basal skull fracture or from a congenital defect (especially pneumococcus).
• In neonates: maternal infection, prolonged rupture of membranes, difficult delivery, prematurity, spina bifida or a dermal sinus.

Pathogenesis

• Bacteria reach the meninges mainly through the blood, or directly from sinusitis, mastoiditis or skull osteomyelitis.
• Bacterial wall products open the blood-brain barrier; cytokines bring in neutrophils and fibrin, and the meninges become coated with pus (over the frontal lobes and vertex in pneumococcal disease, and at the base of the brain).
• Low CSF glucose comes from poor glucose transport across the inflamed choroid plexus and increased use.
• Basal exudate traps cranial nerves and blocks CSF flow (hydrocephalus); vasculitis and venous thrombosis cause infarcts.
• Killing the bacteria with antibiotics releases more cell wall fragments, briefly worsening inflammation: this is why dexamethasone is given before or with the first dose.

Clinical features

Older infants and children

• A preceding upper respiratory or gut upset is common.
• Fever, headache, projectile vomiting, photophobia, irritability, lethargy.
• Neck stiffness, Kernig sign (pain on straightening the knee with the hip flexed to 90 degrees) and Brudzinski sign (the hips and knees flex when the neck is bent). These signs are reliable mainly after 12 months.
• Seizures in about 20-30%, usually in the first 3 days; early seizures from oedema are not a bad sign, but seizures hard to control or beyond day 4 carry a poor outlook.
• Cranial nerve palsy (the sixth is commonest), hemiplegia (in late presenters), ataxia, coma.
• Onset is rapid (under 24 hours) with meningococcus and pneumococcus, and slower (2-3 days) with Hib.

Neonates and young infants

• Signs are subtle: fever in only about half; hypothermia, poor feeding, vomiting, lethargy, irritability, apnoea, seizures.
• Bulging anterior fontanelle, head retraction and a high-pitched cry are late signs of established disease.

Raised intracranial pressure

Headache, vomiting, bulging fontanelle, separated sutures in infants. Ptosis, sixth nerve palsy, unequal pupils, bradycardia with hypertension and apnoea point to herniation. Papilloedema is uncommon and should raise the possibility of sinus thrombosis, subdural empyema or abscess.

Meningococcal disease

A purpuric or petechial rash, mottled skin, cyanosis, a very fast pulse, unrecordable blood pressure and coma. With DIC and adrenal haemorrhage this fulminant picture is the Waterhouse-Friderichsen syndrome.

Investigations

Lumbar puncture

Done between L3 and L5 after checking the fundi. Delay it (and start antibiotics after a blood culture) if there is:

• Raised intracranial pressure, especially with focal neurological signs, poorly reactive pupils or a tense fontanelle.
• Cardiorespiratory instability or shock.
• Skin infection over the puncture site.
• A bleeding disorder or low platelets.

CSF findings

• Always compare CSF glucose with a blood glucose taken just before the tap.
• Gram stain: meningococcus are Gram-negative intracellular diplococci, pneumococcus Gram-positive diplococci, Hib Gram-negative coccobacilli, E. coli Gram-negative bacilli.
• Culture yield falls after antibiotics; PCR and antigen tests (latex agglutination, ELISA) help in partially treated cases. CSF lactate is raised in bacterial disease.
• Newborn CSF normally contains more cells and protein than in older children.

Other tests

• Blood count: leucocytosis with neutrophils.
• Blood culture: positive in most cases (Nelson gives about 90%).
• Gram stain of skin purpura may show meningococci.
• Glucose, electrolytes (look for low sodium from SIADH).
• CT or ultrasound if focal signs, prolonged coma, seizures after 72 hours, persisting irritability, a rapidly growing head, abnormal CSF that will not clear, or relapse.

Differential diagnosis

Tuberculous meningitis, viral (aseptic) meningitis and encephalitis, brain abscess, brain tumour and cerebral malaria.

Management

Antibiotics (start immediately after cultures)

• Akbar gives vancomycin 60 mg/kg/day in four divided doses with the cephalosporin; meropenem is an alternative.
• Ampicillin is needed for Listeria, which cephalosporins do not cover.
• Change to a narrower drug once the organism and sensitivities are known (for example benzylpenicillin for sensitive meningococcus or pneumococcus).

Duration

Dexamethasone

• 0.6 mg/kg/day in divided doses for 2-4 days (Akbar; Nelson gives 0.6-0.8 mg/kg/day for 2 days).
• Give it just before or together with the first antibiotic dose; given after the antibiotic has started lysing bacteria it probably does not help.
• It reduces hearing loss and neurological deficit, proven mainly for Hib meningitis.

Supportive care

• The first 3-4 days are the most dangerous: frequent vital signs, conscious level, pupils and cranial nerves.
• Daily head circumference under 18 months; strict intake-output, daily weight and sodium.
• Fluid restriction to about 60-75% of maintenance for fear of SIADH, but not in shock, because cerebral perfusion must be kept up.
• Seizures: IV diazepam, then phenobarbitone (loading 10 mg/kg, then 5 mg/kg/day) or phenytoin.
• Raised ICP: head up 30 degrees, mannitol; aspirate a symptomatic subdural effusion.
• Treat shock and DIC (fluids, inotropes) in meningococcaemia.

Complications

Prognosis

• Mortality: about 25% pneumococcal, 15% meningococcal, 8% Hib.
• About 35% of survivors have lasting deficits (deafness, seizures, learning difficulty, blindness, paresis, hydrocephalus), more after pneumococcus.
• Poor outlook: young age, long delay before antibiotics, coma or shock at presentation, late or difficult seizures, few CSF cells with many organisms, SIADH, immune deficiency.
• Meningococcal danger signs: purpura spreading within 12 hours, hypotension, coma, DIC, no leucocytosis, low platelets, and meningococcaemia without meningitis.
• Every child must have a hearing test before discharge and at follow-up.

Prevention

• Vaccines: Hib and pneumococcal conjugate vaccines from 2 months of age (part of the routine programme), and meningococcal vaccine (A, C, Y, W135) for high-risk groups, travellers and outbreaks. Schedules change, so follow the current national immunisation schedule.
• Rifampicin chemoprophylaxis for household and close contacts:
  • Meningococcus: 10 mg/kg (maximum 600 mg) every 12 hours for 2 days.
  • Hib: 20 mg/kg/day (maximum 600 mg) once daily for 4 days, for all household members when an unvaccinated child under 4 lives in the home.
  • Ciprofloxacin or ceftriaxone are alternatives (Nelson).
• The index case with Hib or meningococcus also needs rifampicin before discharge, because the treatment course may not clear throat carriage.

Quick revision

• Commonest in infancy; peak 6-12 months; 95% between 1 month and 5 years.
• Neonate: E. coli, GBS, Listeria. Infant: Hib, pneumococcus. Older: meningococcus, pneumococcus.
• Infants: poor feeding, irritability, bulging fontanelle; neck signs unreliable under 1 year.
• CSF: turbid, neutrophils, high protein, glucose under two-thirds of blood.
• No LP with raised ICP and focal signs, shock, bleeding disorder or local infection; never delay antibiotics.
• Ceftriaxone or cefotaxime plus vancomycin; add ampicillin under 2 months.
• Dexamethasone before or with the first dose; reduces deafness.
• Subdural effusion, SIADH, hydrocephalus, deafness; hearing test for all.
• Rifampicin for contacts of meningococcal and Hib cases.

Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).

FAQ