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Probability diagnosis



Alcohol excess

Drug withdrawal incl. alcohol, hypnotics

Head injury

Serious disorders not to be missed


  • Cerebral insufficiency incl. TIAs

  • Acute coronary syndrome

  • Cardiac arrhythmias

  • Subdural or extradural haematoma


  • Any systemic infection esp. sepsis

  • Cerebral e.g. meningitis, abscess



  • Cerebral tumour


  • Kidney failure

  • Hepatic failure

  • Respiratory failure e.g. COPD

  • Electrolyte disturbance

  • Dehydration

  • Post-ictal state

  • Psychosis

Pitfalls (often missed)

Iatrogenic-drugs incl. serotonin syn.



Sleep apnoea


  • Fat embolism

  • Wernicke’s encephalopathy

  • Prion disorders esp. CJS

  • Vitamin deficiency e.g. B1 and B12

Masquerades checklist


Diabetes: ketoacidosis, hypoglycaemia

Drugs (see list)

Thyroid/other endocrine—hyper/hypothyroid?

Urinary tract infection—nocturia

Is the patient trying to tell me something?

A consideration if nil findings.

Key history

A careful history is required incl. an interview with family members and witnesses.

Investigate the onset and circumstances of the behaviour, any possible bizarre behaviour. Past medical history including diabetes, hypertension, cerebrovascular disease. Drug history esp. alcohol or illicit drugs, prescription and OTC drugs.

Check thyroid status, esp. hyperthyroidism.

Key examination

  • General features: appearance of patient incl. evidence of central cyanosis, hydration status, vital signs incl. BMI

  • Head and neck

  • General respiratory and cardiovascular examination

  • Possible source of infection

  • Neurological examination

  • Mental state examination

Key investigations

First line:

  • urinalysis

  • blood sugar

  • pulse oximetry

  • FBE

  • ESR

  • U&E

  • calcium

Others according to history and findings


  • CXR

  • ECG

  • cardiac enzymes

  • TFTs

  • LFTs (γGT)

  • CT scan

  • CSF analysis

Diagnostic tips

Pay close attention to drug use, esp. alcohol, psychotrophics, narcotics, illicit agents, anticholinergics, digoxin, corticosteroids, benzodiazepines esp. if desperate request for drugs.

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