Coma and alteration of consciousness
Coma is a common and important medical emergency, accounting for 3% of acute hospital admissions. This section discusses the terminology used in this field, which is often confusing, then considers the aetiology and pathogenesis of coma, then outlines a pragmatic approach to these patients.
Aetiology and pathogenesis
Consciousness depends on the intact functioning of the reticular activating system in the brain stem and the cerebral cortex. Coma and altered consciousness arise from disturbance of these elements (Table 1). This can arise from:
supratentorial lesions – large enough to cause herniation (p. 48) or large enough to disrupt the cortex
| Site of disease | Causes |
|---|---|
| Infratentorial |
Coma
The clinical assessment of coma is outlined in Box 1. Coma is usually readily recognizable. Potential differential diagnoses include:
‘Locked in syndrome’: This results from a high midbrain lesion or a severe generalized neuropathy, which prevent the patient from all movement despite having a normal consciousness.
The next issue is to determine the cause so as to direct future management of the coma (Box 1). This can be broadly divided into the following categories:
Coma with neck stiffness. This can arise from meningitis, subarachnoid haemorrhage and, rarely, as a result of foramen magnum herniation.
