Altered mental status (AMS) is a non-specific clinical presentation characterised by a change in a patient’s level of consciousness, cognition, awareness, behaviour, or orientation. Rather than representing a diagnosis, AMS is a clinical manifestation of numerous underlying conditions, many of which require urgent investigation and treatment.

The clinical presentation of AMS is highly variable and may range from subtle cognitive impairment to profound unconsciousness. Patients may exhibit confusion, disorientation, agitation, lethargy, impaired attention, behavioural changes, memory disturbance, reduced responsiveness, or coma. Symptoms may develop abruptly over minutes or hours, or evolve gradually over days, depending on the underlying pathology.

The differential diagnosis of altered mental status is broad and encompasses neurological, metabolic, infectious, toxicological, psychiatric, and systemic disorders. Common causes include:

• Neurological disorders, including acute stroke, intracranial haemorrhage, traumatic brain injury, seizures, post-ictal states, central nervous system infections, and intracranial neoplasms.
• Metabolic and endocrine disturbances, such as hypoglycaemia, hyperglycaemia, electrolyte abnormalities, uraemia, hepatic encephalopathy, thyroid disorders, and adrenal insufficiency.
• Infectious diseases, including sepsis, meningitis, encephalitis, and severe systemic infections.
• Respiratory and cardiovascular conditions resulting in cerebral hypoxia, hypercapnia, hypotension, or impaired cerebral perfusion.
• Drug- and toxin-related causes, including intoxication, overdose, withdrawal syndromes, adverse drug reactions, and polypharmacy.
• Psychiatric disorders, including acute psychosis and severe mood disorders, although organic causes should always be excluded before attributing symptoms solely to psychiatric illness.

The initial assessment of a patient presenting with altered mental status should follow a structured clinical approach. Immediate evaluation of the airway, breathing, and circulation (ABC) is essential, together with rapid identification and correction of immediately reversible causes such as hypoglycaemia, hypoxia, or opioid toxicity where appropriate.

Neurological assessment should include evaluation of consciousness using validated tools such as the ACVPU Consciousness Scale or the Glasgow Coma Scale (GCS). Additional assessment should include vital signs, pupillary examination, focal neurological examination, blood glucose measurement, and a focused history obtained from the patient, relatives, carers, or emergency personnel whenever possible.

Diagnostic investigations should be directed by the clinical presentation and differential diagnosis. These may include laboratory investigations, arterial or venous blood gas analysis, electrocardiography, toxicology screening, neuroimaging with computed tomography (CT) or magnetic resonance imaging (MRI), electroencephalography (EEG), and lumbar puncture where central nervous system infection is suspected and no contraindications exist.

Clinical prediction tools and neurological scoring systems may assist in documenting disease severity and monitoring progression; however, they should be regarded as adjuncts to, rather than substitutes for, comprehensive clinical assessment and professional judgement.

Early recognition of altered mental status and a systematic diagnostic approach are essential to optimising patient outcomes. Prompt identification of reversible causes, timely initiation of appropriate treatment, and early escalation of care when indicated are fundamental principles in the management of patients presenting with altered consciousness or cognitive dysfunction.