NEUROLOGICAL ASSESSMENT OF
David E Bateman
he neurologist is often required to evaluate the unconscious patient from both the
diagnostic and prognostic perspective. Knowledge of the anatomical basis of coma is
essential for competent evaluation but must be combined with an understanding of the
many, often multi-factorial, medical conditions that result in impaired consciousness.
Consciousness is a state of awareness of self and the environment. This state is determined by
two separate functions:
awareness (content of consciousness)
arousal (level of consciousness ).
These are dependant upon separate physiological and anatomical systems. Coma is caused by
disordered arousal rather than impairment of the content of consciousness, this being the sum of
cognitive and a
ective mental function, dependent on an intact cerebral cortex. The absence of all
content of consciousness is the basis for the vegetative state.
Arousal depends on an intact ascending reticular activating system and connections with dien-
cephalic structures. Like awareness, arousal is not an all or nothing concept and gradations in
awareness have been described in the past as inattentiveness, stupor, and obtundation. Such terms
lack precision and coma can be more objectively assessed using measures such as the Glasgow
coma scale (GCS) (table 1). This analyses three markers of consciousness—eye opening, and
motor and verbal responses—bringing a degree of accuracy to evaluation.
The GCS arbitrarily deﬁnes coma as a failure to open eyes in response to verbal command (E2),
perform no better than weak ﬂexion (M4), and utter only unrecognisable sounds in response to
pain (V2). The GCS is of no diagnostic value, but is a reliable way of objectively monitoring the
clinical course of the patient with an acute cranial insult without elucidating cause.
NEUROANATOMICAL BASIS OF COMA
Clinicopathological correlation and neurophysiological experimentation has shown that coma is
caused by di
use bilateral hemisphere damage, failure of the ascending reticular activating
system, or both. The reticular activating system is a core of grey matter continuous caudally with
the reticular intermediate grey lamina of the spinal cord and rostrally with the subthalamus,
hypothalamus, and thalamic nuclei. It runs in the dorsal part of the brain stem in the paramedian
A unilateral hemisphere lesion will not result in coma unless there is secondary brain stem
compression, caused by herniation, compromising the ascending reticular activating system.
Extensive bilateral damage or disturbance of the hemisphere function is required to produce coma.
Bilateral thalamic and hypothalamic lesions also cause coma by interrupting activation of the cortex
mediated through these structures. In hypothalamic lesions, phenomena associated with sleep, such
as yawning, stretching, and sighing, are prominent. The speed of onset, site, and size of a brainstem