The neurological examination in coma

The neurological examination in coma
This is aimed at locating the pathology in 1 of 2 places. Altered level of consciousness implies either (1) a diffuse, bilateral, cortical dysfunction (usually producing loss of awareness with normal arousal) or (2) damage to the ascending reticular activating system (ARAS) located throughout the brainstem from the medulla to the thalami (usually producing loss of arousal with unassessable awareness). The brainstem can be affected directly (eg pontine haemorrhage) or indirectly (eg compression from trans-tentorial or cerebellar herniation secondary to a mass or oedema).
Level of consciousness; describe using objective words.
Respiratory pattern Cheyne-Stokes, hyperventilation (acidosis, hypoxia, or rarely, neurogenic), ataxic or apneustic (breath-holding) breathing (brainstem damage with grave prognosis).
Eyes almost all patients with ARAS pathology will have eye findings.

Visual fields
In light coma, test fields with visual threat. No blink in 1 field suggests hemianopsia and contralateral hemisphere lesion.

Pupils
Normal direct & consensual = intact midbrain. Midposition (3-5mm) non-reactive ± irregular = midbrain lesion. Unilateral dilated & unreactive (fixed) = 3rd nerve compression. Small, reactive = pontine lesion (‘pinpoint pontine pupils’) or drugs. Horner's syndrome = ipsilateral lateral medulla or hypothalamus lesion, may precede uncal herniation. Beware patients with false eyes or who use eye drops for glaucoma.

Extraocular movements (EOMs)
observe resting position and spontaneous movement; then test the vestibulo-ocular reflex (VOR) with either the Doll's-head manoeuvre (normal if the eyes keep looking at the same point in space when the head is quickly moved laterally or vertically) or ice water calorics (normal if eyes deviate towards the cold ear with nystagmus to the other side). If present, the VOR exonerates most of the brainstem from the VII nerve nucleus (medulla) to the III (midbrain). Don't move the head unless the cervical spine is cleared.

Fundi
papilloedema, subhyaloid haemorrhage, hypertensive retinopathy, signs of other disease (eg diabetic retinopathy).
Examine for CNS asymmetry (tone, spontaneous movements, reflexes).