10.5 Dual diagnosis and substance related complications

What dual diagnosis means

• Dual diagnosis usually means mental illness with substance misuse, though in other settings it means intellectual disability with mental illness.

• ICD-11 codes substance-induced syndromes separately from independent mental disorders, and the link may stay provisional while treatment goes on.

Telling induced from independent disorders

• An observation period must not delay needed treatment, and psychological treatment can start while someone is still drinking.

Substance-induced psychosis

A meta-analysis of 50 studies found that 25% of people first diagnosed with substance-induced psychosis later received a schizophrenia diagnosis.

Integrated care

• Use one care plan with a named lead, an intervention for each condition and a crisis response, because treating one condition while the other waits can leave both untreated.

• NICE CG120 covers people aged 14 and over with psychosis and substance misuse, and treats most adults in secondary mental health services.

• NICE NG58 covers severe mental illness with substance misuse in community health and social care, and asks services to adapt existing provision rather than build a separate dual diagnosis service.

• People should not be excluded from mental health care for using substances, or from addiction care for having psychosis.

Delirium tremens and alcoholic hallucinosis

The two are told apart by consciousness: it is clouded in delirium tremens and clear in hallucinosis.

• Alcoholic hallucinosis is called alcohol-induced psychotic disorder in ICD-11, and is diagnosed only without a primary psychosis.

• It is bound to drinking: it arises with use, clears on abstinence and returns on relapse, whereas schizophrenia runs independently of alcohol.

• Hallucinations that persist respond to antipsychotics.

• Othello syndrome (pathological jealousy) is a delusion of a partner's infidelity, usually standing alone and most often linked to current or past alcohol misuse, with a risk of violence to the partner.

Blackouts, head injury and drug reactions

• An alcoholic blackout is anterograde amnesia for a drinking episode during which consciousness and conduct were normal, with earlier and remote memories intact.

• In the partial (fragmentary) blackout, recall is patchy and cues can restore it; the en bloc form is complete.

• Chronic subdural haematoma presents with a fall weeks earlier, worsening headache, fluctuating drowsiness and focal weakness.

• Heavy drinkers are prone to subdural haematoma through falls, brain atrophy stretching the bridging veins, and poor clotting.

• Metronidazole causes a disulfiram-like reaction soon after drinking (flushing, throbbing headache, palpitations, nausea, hypotension).

• UK advice is to avoid alcohol during a metronidazole course and for 48 hours after it.

Suicide

• Lifetime risk of death by suicide in alcohol dependence is about 7% (roughly 1 in 14).

• The classically quoted figure is 10 to 15%, against about 4% for alcohol problems as a whole and about 1% in the general population.

• Psychosocial assessment after self-harm should not be withheld because the person is intoxicated, and is completed as soon as they can take part.

Wernicke's encephalopathy

• Wernicke's encephalopathy is caused by thiamine deficiency and gives confusion, ataxia and eye signs, though only a minority show the full triad.

• It arises from any cause of thiamine deficiency (poor intake, malabsorption, increased loss or increased use), not from alcohol alone.

• Two of dietary deficiency, eye signs, ataxia and altered mental state warrant treatment.

• Give urgent high-potency parenteral thiamine, because oral thiamine is too poorly absorbed, and never give glucose or a carbohydrate load before it.

Korsakoff's syndrome

• Korsakoff's syndrome is a chronic amnesic state with a clear sensorium, following Wernicke's encephalopathy in about 80% of survivors.

• Anterograde amnesia, the failure to lay down new memories, is its constant, defining and dominant deficit; temporally graded retrograde loss is secondary.

• Confabulation is inconsistent and fades with chronicity.

• The amnesia is selective: intelligence on the Wechsler Adult Intelligence Scale, attention and working memory are largely preserved while new learning is severely impaired.

• Episodic memory, for personal events and dependent on the hippocampal-diencephalic circuit, is hit hardest; semantic and non-declarative memory are comparatively intact.

• Thiamine, continued beyond the acute phase, is the treatment of choice.

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Other brain syndromes and their neighbours

• Chronic alcohol misuse causes toxic and nutritional brain syndromes, but subcortical small-vessel disease (hypertensive or hereditary) is a vascular dementia not caused by alcohol.

• Acquired hepatocerebral degeneration in alcohol-related cirrhosis has chronic basal ganglia, cerebellar and speech features, whereas asterixis is a sign of acute hepatic encephalopathy.

• Hepatic encephalopathy does not produce ophthalmoplegia, which separates it from Wernicke's encephalopathy.

• Pellagra is deficiency of niacin (vitamin B3, nicotinic acid, nicotinamide), seen with poor diet in alcohol dependence.

• Pellagra shows the four Ds, photosensitive dermatitis on sun-exposed skin (Casal's necklace, backs of the hands), diarrhoea, dementia and death, with neuropsychiatric change.

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Complications of other substances

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• In nitrous oxide myelopathy, serum B12 is normal while homocysteine and methylmalonic acid are raised.

• Evidence that a rise in caffeine intake precipitates a mood episode in bipolar disorder is inconclusive, because it is associational and cannot separate cause from prodrome.

• Tobacco smoke, not nicotine, induces CYP1A2, so stopping smoking can push clozapine levels up within days; nicotine replacement and vaping do not keep the induction going.

Neonatal effects

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• Neonatal abstinence syndrome starts within the first day after heroin but around day 3 after a long-acting opioid such as methadone.

• Flumazenil has occasionally been used to reverse severe sedation in floppy infant syndrome.