Dementia and Cognitive Decline

Psychiatry — Dementia, NMC MBBS licence examination syllabus (Nepal Medical Council).

Dementia: what has been lost, over what time, and what can still be done

The first question is never "which dementia?" — it is "is this dementia at all?"

A 74-year-old is brought in by her daughter, who says she has become forgetful and muddled. That single sentence covers at least four very different situations: a progressive dementia, an acute delirium from an infection nobody has looked for, a depression that impairs concentration, or a hearing loss that has been mistaken for confusion.

Getting this wrong in either direction causes harm. Label a delirium as dementia and you miss a treatable illness happening today. Label a dementia as "just ageing" and the family loses the time they needed to plan.

Delirium or dementia? The distinction that decides everything

This is the highest-yield discrimination in the whole topic, both for the exam and for the patient in front of you.

Three features separate them reliably:

1. Time course. Delirium develops over hours to days. Dementia develops over months to years. If the family can date the change to a particular week, you are almost certainly not dealing with a new dementia.
2. Attention. Delirium impairs attention — the patient cannot hold a thread, drifts off mid-sentence, and cannot follow a simple sequence. In early dementia attention is relatively preserved; it is memory that fails.
3. Fluctuation and consciousness. Delirium waxes and wanes, characteristically worse at night, with clouded awareness. Dementia is comparatively steady, and the patient is fully alert.

The trap is that these are not alternatives. Dementia is the strongest single risk factor for delirium, so the two coexist constantly. In a patient with known dementia, a sudden worsening over days is delirium until proven otherwise — and the cause is usually infection, pain, retention, constipation, dehydration or a new drug. Treat what is treatable before concluding the dementia has simply progressed.

Exclude what is reversible

Before accepting a progressive diagnosis, look for the contributors that can be corrected.

Depression deserves particular attention, because it is the great mimic. Depression in an older person often presents with poor concentration, slowed thinking and apathy — which the family describes as memory loss. The distinguishing feature is that a depressed patient often says "I don't know" and gives up, while a patient with dementia frequently confabulates and tries to cover the gap. Depression is treatable, so it must be actively considered, not assumed absent.

Then check the ordinary things: thyroid function, B12 deficiency, infection, alcohol, and above all the drug chart. Sedatives and anticholinergic drugs impair cognition in older people reliably, and are prescribed constantly. Deafness and poor vision are also mistaken for confusion far more often than anyone admits — a patient who cannot hear the question answers it wrongly.

The subtypes and what distinguishes each

Once a dementia is established, the subtype affects prognosis, management, and one very important prescribing decision.

In practice, mixed pathology is common, particularly in the very old, where Alzheimer and vascular changes frequently coexist. A confident single label is often less honest than acknowledging the mixture.

The prescribing error that can kill

If you remember one management point from this chapter, make it this one.

Patients with Lewy body dementia can react catastrophically to antipsychotic drugs — severe rigidity, collapse, and marked irreversible deterioration. This matters enormously in practice, because the situation in which someone reaches for an antipsychotic is precisely the situation Lewy body dementia produces: an older, confused patient with visual hallucinations.

So before any antipsychotic in an older confused patient, ask specifically about visual hallucinations, fluctuating cognition and parkinsonism. If those are present, seek specialist advice rather than prescribing. Doses, choices and monitoring for these drugs are specialist decisions and are not given here.

And ask why the patient is distressed before treating the distress. Agitation in dementia usually has a reason: pain, urinary retention, constipation, hunger, fear, over-stimulation, or an unfamiliar environment. These are common, findable and correctable. Sedating a patient whose real problem is a full bladder treats the observer, not the patient.

Management, most of which is not a drug

Diagnose early and explain honestly. An early diagnosis gives the person time while they still have capacity — to settle their affairs, to say what treatment they would want later, and to nominate who should speak for them. That window closes, and it does not reopen.

Support the carer, because the carer is the treatment. Most people with dementia are looked after at home by a family member, usually with little support. Carer exhaustion is what ends home care more often than the illness itself. Asking the carer how they are managing is a clinical intervention, not a courtesy.

Simplify the environment and the drug chart. Routine, familiar surroundings, good lighting, working hearing aids and correct glasses all reduce confusion. Every sedating or anticholinergic drug should be justified again.

Drugs for cognition — cholinesterase inhibitors and memantine — help some patients modestly with symptoms. They do not halt the underlying disease, and expectations should be set accordingly. Choice, dose and monitoring are specialist matters.

Capacity is decision-specific

A diagnosis of dementia does not remove the right to make decisions. Capacity is assessed for a particular decision at a particular time, and many people with dementia retain it for a great deal — where to live, what to eat, whether to accept a treatment — long after they have lost it for complex financial matters.

Fluctuation matters too: a patient may have capacity in the morning and not in the evening, or before and not during a delirium. The general framework for consent and capacity is covered in the ethics chapter; the point here is simply that the label is not the assessment.

Putting it together

1. Ask "is this delirium?" first. Days not months, attention impaired, fluctuating — and it coexists with dementia constantly.
2. Exclude depression, drugs, thyroid, B12, infection, deafness and poor vision before accepting a progressive diagnosis.
3. Know one distinguishing feature per subtype, and treat visual hallucinations plus parkinsonism as a warning against antipsychotics.
4. Look for a cause of distress before sedating anyone.
5. The carer is the treatment. Support them, or home care ends.

Cognitive test cut-offs, drug choices and doses are deliberately not quoted here — screening instruments vary by version and require adjustment for education and language, and the drugs are specialist-initiated. Use your current local protocol.

Syllabus points

• Delirium vs dementia — time course, attention, fluctuation
• Why they coexist, and what a sudden worsening means
• Reversible causes: depression, drugs, thyroid, B12, sensory loss
• The four subtypes and one distinguishing feature each
• Antipsychotic sensitivity in Lewy body dementia
• Non-drug management and supporting the carer
• Capacity is decision-specific

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Related topics in Dementia

• Dementia — Practice Questions