Syndromes of cognitive impairment

As described on page 7, organic disorders are ‘diseases of the body’ which present with psychiatric symptoms. In contrast, functional psychiatric disorders are considered to be ‘diseases of the mind’. Classifying psychiatric disorders in this way is becoming outdated now that more is known about the ‘organic’ basis of functional illnesses, such as abnormal brain structure in schizophrenia. However, the term organic is still commonly used and is included in ICD10. Organic disorders will be described in this section, starting with syndromes of cognitive impairment.

Delirium and dementia

In both dementia and delirium, there is a generalised impairment of brain function which causes global impairment in cognitive function and altered mood and behaviour. The difference between the two is that delirium is an acute syndrome characterised by fluctuating levels of consciousness and attention whereas dementia is a chronic syndrome which occurs in clear consciousness without rapid fluctuations. Both conditions are more common in older people, but the diagnoses need to be considered in any patient who presents with a generalised impairment of brain function.

Delirium

In delirium a group of characteristic symptoms occur as a result of an acute, generalised impairment of brain function. The most common causes are shown in Table 1. Delirium is more likely to occur in children, when the brain is still developing, and in the elderly, when the brain is starting to degenerate. People with dementia are particularly at risk and so it is always important to rule out a superimposed delirium if the cognitive function of people with dementia deteriorates acutely. Another high risk group is people admitted to elderly medicine wards – studies have found 15–50% show evidence of delirium.

Table 1 Causes of delirium

Intoxication with drugs	Anticholinergics Anticonvulsants Anxiolytics/hypnotics Digoxin L-dopa Corticosteroids Alcohol Solvents Illicit drugs
Drug withdrawal	Alcohol Benzodiazepines
Systemic	Infection Endocrine hypoglycaemia hyperparathyroidism Addison’s disease Metabolic electrolyte imbalance hypoxia renal failure liver failure thiamine deficiency porphyria
Neurological	Infections meningitis encephalitis Raised intracranial pressure Space occupying lesions Head injury Epilepsy epileptic status post-ictal states

The patient’s level of consciousness and attention fluctuates, often with a diurnal pattern, usually being worse at night. They are drowsy with a reduced response to external stimuli at times, and at other times are hypervigilant and distractable. Other common features are disorientation, impaired recall, disturbances of the sleep–wake cycle, persecutory delusions, perceptual disturbance and emotional disturbance. These features are summarised and contrasted with typical symptoms of dementia in Table 2.

Table 2 Features of delirium and dementia

	Delirium	Dementia
Onset	Acute, usually within hours or days	Gradual, usually at least 6 months
Diurnal variation	Yes, usually worse at night	May be worse at night
Duration	Days or weeks, usually less than 6 months	Months or years
Consciousness/Alertness	Drowsy or hypervigilant	Normal
Attention	Usually poor	Usually maintained
Orientation	Disorientated in time, often in place and person	Similar changes but later in course of illness
Instant recall	Impaired	Only impaired in late stages
Memory	Impaired	Impaired
Thinking	Increased, reduced or muddled	Reduced
Delusions	Common	Occur, but less common
Illusions/Hallucinations	Common, usually visual	Only occur in late stages
Sleep	Reversal of sleep–wake cycle common	Insomnia in some cases