Causes of Coma in the Elderly

Causes of Coma in the Elderly Fifteen–Twenty High-Yield Points Definition and anatomy

Coma is a state of unarousable unresponsiveness — the deepest grade on the scale of consciousness used in delirium assessment: alert, vigilant, lethargic, stupor (difficult to arouse), and coma (unarousable).

Consciousness requires two components: arousal, dependent on the ascending reticular activating system in the brainstem and its thalamic projections, and awareness, dependent on the cerebral cortex. Coma therefore requires either a brainstem lesion, bilateral hemispheric dysfunction, or a diffuse metabolic insult. A single unilateral hemispheric lesion causes coma only if it produces mass effect and herniation.

In the elderly, the threshold for coma is lower because of reduced neuronal reserve, pre-existing cognitive impairment, polypharmacy and multimorbidity — the same insult that causes mild confusion in a young adult may cause coma in an older person.

Hypoglycaemia is the single most important immediately reversible cause and must be excluded at the bedside in every patient — particularly in older people on sulphonylureas or insulin with declining renal function or poor intake.

Other metabolic causes listed among the causes of delirium and confusion, and which at their extreme produce coma: hypoxia, hypercarbia, hyperglycaemia, hyponatraemia and azotaemia.

Hyperglycaemic emergencies: hyperosmolar hyperglycaemic state is the characteristic presentation in the elderly and carries high mortality; diabetic ketoacidotic coma is less common in this age group.

Endocrine: myxoedema coma (hypothermia, bradycardia, hyponatraemia, precipitated by infection or cold) and adrenal (Addisonian) crisis; both are classic geriatric causes of unexplained coma with hypothermia.

Organ failure: hepatic encephalopathy, uraemic encephalopathy, carbon dioxide narcosis in type 2 respiratory failure, and severe hypothyroidism.

Electrolyte and mineral disturbance: severe hyponatraemia (and over-rapid correction causing osmotic demyelination), hypercalcaemia (often malignancy-related), and severe hypo- or hypermagnesaemia.

Nutritional: Wernicke's encephalopathy from thiamine deficiency — frequently missed in older patients with poor intake, malignancy or after refeeding, and not confined to alcohol misuse.

Drugs and toxins are among the commonest causes: opioids, benzodiazepines, tricyclic antidepressants, anticholinergics, lithium, anticonvulsants, alcohol intoxication, and carbon monoxide poisoning. Polypharmacy and altered pharmacokinetics make the elderly especially vulnerable, and drug intoxication is explicitly listed among the causes of acute confusional states.

Thermal: hypothermia and hyperthermia are listed causes; both are more frequent in older people because of impaired thermoregulation, and heat stroke is an increasing problem in Indian summers.

Stroke: massive hemispheric infarction with cerebral oedema (malignant MCA infarction) causing midline shift, raised intracranial pressure and transtentorial herniation with brainstem compression; and brainstem or bilateral thalamic infarction, where coma occurs directly.

Intracerebral haemorrhage, especially with intraventricular extension or cerebellar haemorrhage — where surgical evacuation of a cerebellar haematoma is a life-saving measure.

Subarachnoid haemorrhage: sudden severe headache with vomiting, neck stiffness, altered conscious level and collapse. Mortality is 35–65%, and outcome is predicted by Glasgow Coma Scale score, age and the volume of intracranial blood.

Subdural haematoma is a particularly geriatric diagnosis. It occurs with trivial trauma and sometimes without any trauma, especially in those taking anticoagulants, and may present as fluctuating consciousness or confusion. Poor outcome is predicted by advanced age, low GCS at presentation, comorbid injuries and anticoagulant use.

Intracranial infection: bacterial meningitis, encephalitis (herpes simplex), cerebral abscess and, in India, tuberculous meningitis with hydrocephalus — where the classical triad may be absent and confusion or coma may be the only feature.

Space-occupying lesions: primary and metastatic brain tumours; brain tumours are responsible for 10–30% of new seizures in the elderly and may present with progressive obtundation from oedema.

Seizure-related: post-ictal state, and importantly non-convulsive status epilepticus, which in older patients may present as unexplained prolonged coma without motor manifestations and requires EEG for diagnosis. Cerebrovascular disease is the leading cause of seizures and status epilepticus in later life.

Approach: stabilise airway, breathing and circulation; check capillary glucose immediately; give thiamine before glucose where deficiency is possible; consider naloxone; measure temperature; assess GCS, pupils, brainstem reflexes and any focal or lateralising signs; take a full drug and collateral history; obtain urgent non-contrast CT brain; and perform lumbar puncture once mass effect is excluded. Remember that coma in the elderly is frequently multifactorial, and treatable contributors such as sepsis, hypoxia, hypoglycaemia and drug toxicity should all be corrected simultaneously.