Coma

A child who is deeply unconscious is said to be in coma. Encephalopathy refers to the precomatose state with an altered conscious level. An unconscious child requires urgent and careful evaluation to establish the cause of the coma and to commence appropriate therapy. Whatever the cause the airway must be protected and adequate ventilation maintained.

Meningitis

Meningitis is caused by either bacterial or viral infection invading the membranes overlying the brain and spinal cord and should be considered in any irritable child with unexplained fever. It is commonest in the neonatal period but can occur at any age. The causes are listed in the box.

Viral meningitis is preceded by pharyngitis or gastrointestinal (GI) upset. The child then develops fever, headache and neck stiffness. In bacterial meningitis the child is drowsy and may be vacant. Irritability is a common feature, often with a high-pitched cry, and convulsions may occur. Examination shows an ill child, with a stiff neck and positive Kernig’s sign (pain on extending the legs). These signs are not reliable in young infants. Tonsillitis and otitis media can also mimic neck stiffness. In infants the fontanelle may be bulging. A petechial or purpuric rash suggests meningococcal meningitis.

Meningitis is confirmed by a lumbar puncture (see Chapter 5), which shows a leucocytosis, high protein count, low glucose and may show organisms present. The fluid will look cloudy to the naked eye. Culture or PCR analysis will confirm the organism, but treatment should be commenced empirically as soon as the cultures have been taken.

Intravenous ceftriaxone is usually given, depending on the age of the child and the likely organism. Steroids reduce meningeal inflammation in haemophilus meningitis. Meninigococcal meniningitis is associated with pharyngeal carriage and household contacts should receive prophylaxis with rifampicin. Meningococcal septicaemia is discussed in Chapter 52.

Encephalitis

Viral infection sometimes spreads beyond the meninges to infect the brain tissue itself. This is known as meningo-encephalitis. The onset is often more insidious and the child’s personality may change or they may become confused or clumsy before the onset of coma. Meningism is less of a feature. The lumbar puncture shows a lymphocytosis and specimens should be sent for viral culture and PCR analysis. Herpes simplex virus or Mycoplasma pneumoniae may be responsible, so always ask about contact with herpetic lesions (cold sores). Treatment with aciclovir, erythromycin and cefotaxime is given until the organism is known.

In herpes encephalitis the EEG and an MRI brain scan may characteristically show temporal lobe involvement.

Metabolic Causes of Coma

In the absence of trauma or infection, a metabolic cause for coma must be considered. By far the commonest metabolic cause is hypoglycaemia, and blood glucose must be measured immediately at the bedside in every unconscious child. Hypoglycaemia may be due to inadequate carbohydrate intake or excess insulin in children with diabetes mellitus, but it can also be the presenting feature in infants with inborn errors of metabolism or adrenal insufficiency. Hyperglycaemia in uncontrolled diabetes can lead to ketoacidosis with coma, though the onset is often more gradual. Diabetes is discussed in detail in Chapter 18.

Any severe metabolic derangement can cause coma, including severe uraemia (in renal failure) or high ammonia (inborn errors of metabolism such as urea cycle disorders), severe hypernatraemia or hyponatraemia. Coma can also be caused by cerebral oedema from over-rapid correction of electrolyte imbalance in severe dehydration.

Reye’s Syndrome

Reye’s syndrome may be preceded by a viral illness such as influenza or chickenpox, and is commoner in winter. Although it is rare and not in itself infectious it can be triggered by the use of aspirin (salicylic acid) during a viral illness and hence aspirin is not recommended in childhood. The exact aetiology is unknown, but there is an initial phase of vomiting and lethargy followed by a non-inflammatory encephalopathic illness with personality change, irritability and then coma with raised intracranial pressure. Fatty change (steatosis) in the liver may lead to acute hepatic failure. Treatment is mainly supportive with aggressive intensive care treatment to treat raised intracranial pressure.

Unexplained Coma

In unexplained coma the possibility of non-accidental injury such as shaking injury must be considered. A CT brain scan and skeletal survey may show evidence of trauma and retinal haemorrhages may be present. Accidental drug ingestion or overdose, or deliberate poisoning may cause coma, and a urine toxicology screen can sometimes identify the drug. Drugs affecting the central nervous system such as opiate analgaesics, alcohol and antidepressants are often implicated.