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Probability diagnosis

Functional: no medical or mental component

Drugs: alcohol, illicit (see list) or prescribed

Alcohol: acute or chronic

Antisocial personality disorder esp. cluster B

Affective (mood) disorders

Drug withdrawal incl. alcohol, hypnotics

Mental impairment

Serious disorders not to be missed


  • Cerebrovascular disease including SAH

  • Acute coronary syndromes


  • Encephalitis/meningitis


  • Septicaemia


  • Cerebral tumours


  • Post ictal (epilepsy)

  • Delirium

  • Subdural haematoma

  • Psychosis: schizophrenia, bipolar, paraphrenia

  • Schizotypal personality disorder

Pitfalls (often missed)

Head injury

Fluid and electrolyte imbalance

Dementia esp. early


  • Neurosyphilis

  • Prion disease e.g. CJD

  • Premenstrual dysphoria syndrome

Masquerades checklist


Diabetes: hypoglycaemia

Drugs: iatrogenic/social–illicit

Thyroid/other endocrine: hyper/hypothyroid

Is the patient trying to tell me something?

Consider conversion disorder (hysterical fugue)


Severe anxiety/panic

Key history

  • Nature of behaviour and precipitants, associations

  • Psychiatric history: anxiety, OCD, depression, hypomania, personality traits, fugue features

  • Past, family and psychosocial history, developmental history, epilepsy, Parkinson disease, family history

  • Drug history: prescribed (see list), OTC, alcohol, social/illicit drugs (see list)

Key examination

This is limited.

  • General features: appearance and behaviour of patient, vital signs

  • General respiratory, neurological and cardiovascular examination

  • Pulse oximetry

  • Mental state examination

Key investigations

First line:

  • urinalysis

  • blood glucose

  • FBE

  • U&E


  • LFTs (γGT)

  • ECG

  • TFTs

  • KFTs

  • cerebral imaging

Diagnostic tips

Pay close attention to drug use esp. alcohol, caffeine, narcotics and amphetamines e.g. ‘ice’

Prescribed drugs: major and minor tranquilisers, anti-Parkinson, cardiogenic, corticosteroids.

Non-prescribed drugs: marijuana, LSD, opioids, amphetamines, ecstasy, cocaine, gamma hydroxybutyrate (‘fantasy’), solvents e.g. petrol sniffing.

Cluster B antisocial personality disorders incl. histrionic, narcissistic and borderline.

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