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6th August 2024
Causes of altered consciousness level
The table that follows is not an exhaustive list but touches upon the major differential diagnoses encountered in day-to-date clinical practice, as well as diagnoses favoured in the MRCP exams.
| System | Aetiology | Important special considerations |
|---|---|---|
| Neurological | Seizures | |
| Intracranial haemorrhage | Different sites of haemorrhage provoke distinct clinical syndromes, e.g. the ‘lucid interval’ of extradural haemorrhage
Vasospasm is a common cause of delayed deterioration post-SAH; nimodipine is given to reduce the risk of this |
|
| Infarction (site dependent) | Major infarction can present with altered consciousness; patients with vascular risk factors and a total coma should be urgently evaluated for locked in syndrome (basilar artery thrombus) | |
| Space-occupying lesions and mass effect | ||
| Meningitis and encephalitis | ||
| Cardiovascular | Vasovagal syncope | May present with twitching of arms and legs due to anoxia, and so may be confused with seizure |
| Arrhythmia | ||
| Extremes of blood pressure | ||
| Structural or electrical heart disease | ||
| Cardiac arrest | Neurological prognostication following return of spontaneous circulation can only take place after 72 h of optimal post-ROSC (return of spontaneous circulation) care; after this, lack of motor response is the most sensitive parameter | |
| Respiratory | Hypoxia | |
| Hypercapnia | ||
| Carbon monoxide poisoning | Classically taught ‘cherry-red’ colouration of mucous membranes is rare in practice – assess based on history and blood gas | |
| Renal and metabolic | Hypoglycaemia | |
| DKA and HHS | ||
| Uraemia | May occur if there is an acute deterioration into ESRF and may manifest with fatigue, nausea, itching, encephalopathy, pericarditis | |
| Hepatic encephalopathy | Requires screening for multiple potential precipitants: constipation, electrolyte imbalance, GI bleeding, underlying infection (especially SBP, spontaneous bacterial peritonitis) | |
| Gland failure: thyroid, adrenals, pituitary | All may present with alteration of conscious level – clinical examination may reveal signs suggestive of co-existent autoimmune diseases
Treat with hydrocortisone 200 mg ± glucose until adrenal insufficiency ruled out, IV/NG thyroid hormone replacement if indicated |
|
| Haematological | Thrombotic thrombocytopaenic purpura | Classical pentad: anaemia, thrombocytopaenia, fever, renal and CNS involvement
Testing will demonstrate reduced ADAMTS-13 activity; treatment is with urgent plasma exchange and high dose steroids |
| Psychiatric | Psychogenic non-epileptic seizures | |
| Catatonia | ||
| Delirium | ||
| Other | Trauma | A multiply injured patient with reduced consciousness level should be assessed in the usual trauma ABCDE approach, which may reveal non-neurological causes for CNS dysfunction |
| Drugs and toxins | ||
| Infection and sepsis |
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