Delirium vs Dementia: How to Tell the Difference

Delirium vs dementia is often a question of timing of onset. Most forms of dementia develop gradually over months, indeed years. Delirium is an acute change — often over hours or days — marked by inattention and a mental state that can wax and wane. The practical point for families is this: sudden confusion in an older adult is delirium until proven otherwise. Delirium should also prompt a call to a physician or other clinician to search for an underlying medical cause.

Dr. Justin Mutter, a geriatrician who cares for older adults with dementia, Parkinson’s disease, and complex medical illness, explains the distinction this way: dementia changes the baseline; delirium represents a sudden departure from it.

Key takeaways

• Delirium is sudden; dementia is gradual.
• The most useful family observation is often, “This is <u>not</u> like him.”
• Delirium commonly affects attention and fluctuates hour by hour.
• Sudden confusion should trigger medical evaluation, not an assumption that dementia has abruptly worsened.

“Dr. Mutter, come quickly, Mr. Smith is really confused.” Until this request, it had been a fairly uneventful morning in a rehabilitation facility where I was filling in for a physician colleague, who was on vacation. I hustled down the corridor with the nursing team to find Mr. Smith sitting up in his bed, clearly distressed by something that he struggled to name.

This was my first time meeting him, but my immediate intuition was that this did not reflect his usual state. His wife, recently arrived at his bedside, and the nursing team both corroborated this intuition. Something was off. He did not know where he was, and had difficulty focusing on my questions, much less answering them appropriately.

I examined him: his vital signs were reassuring, but he did seem to have some mild tenderness in his abdomen. He had arrived at the facility just two days ago following a protracted hospitalization from major heart surgery. My brain scanned the list of things that could be wrong: it was long, and ranged widely from minor to major causes. Moreover, it was hard to envision how we could work through that list quickly with the resources in the facility alone.

In conversation with his wife and the nursing team, we decided to send Mr. Smith to the emergency room for rapid assessment.

Unlike “dementia,” “delirium” is a word that is less recognizable to many of us. Delirium and dementia are not the same thing, and yet they are often mistaken for one another. They also often coexist, which further challenges our understanding. For this and for other reasons, delirium is a condition that seems murky to us. Caregivers know enough to be worried about changes in cognition, but discerning <u>what to be worried about</u> is harder.

Assessing Mr. Smith, how did I know that this was delirium and not dementia?

What is the main difference between delirium and dementia?

First, delirium represents an acute change in someone’s cognitive state. The simplest bedside clue is the tempo of change. Delirium is abrupt, whereas dementia is gradual. Daily caregivers thus have a unique window into differentiating the two.

When caring for a confused patient, doctors and nurses know to go to the caregiver and ask, “When was his or her last ‘normal’ state?” The more sudden, and the more definitive the departure from someone’s prior cognitive baseline, the more likely it is that delirium is the culprit.

But the second cardinal feature of delirium complicates a simple determination. One of the hallmarks of delirium is that it tends to wax and wane. Unlike dementia, delirium fluctuates. Those experiencing delirium can seem fully themselves for minutes, even hours, only to become again confused.

Furthermore, delirium can appear to take different forms: in medical speak, delirious persons can be either “hyperactive” or “hypoactive” — and everything in between. Mr. Smith was trending toward hyperactive: he was alert, emotionally distressed, and talkative despite his confusion. But those suffering from delirium can also be sleepy or withdrawn. Sometimes, we see both: hypoactive delirium during one part of the day, and hyperactive states in others. Research has shown that in hospitals, medical staff miss the diagnosis of delirium up to half of the time. Why? Because medical teams often “round” on patients in the early morning hours, and they mistake hypoactive delirium for natural sleepiness.

The final trademark of delirium is that sufferers struggle to <u>attend</u> to a conversation. Attention is the component of cognition most immediately impacted by delirium. Hence why Mr. Smith had tremendous difficulty focusing on my questions. Attention can be altered by dementia too, but it shouldn’t be acutely altered in a notable departure from someone’s prior cognitive capacities. And so here’s the key: to differentiate delirium from dementia, you need <u>all three core features</u><u> at the same time</u>:

1. Acute change — a sudden departure from the person’s usual cognitive state.
2. Inattention — difficulty focusing, tracking a conversation, or staying engaged.
3. Fluctuation — symptoms that wax and wane, often hour by hour.

Can dementia symptoms look like delirium?

Caregivers for those living with dementia may immediatel (and rightly) interject: but those with dementia can fluctuate in their emotions and behaviors throughout the day — how is this different than delirium?

Sundowning, for example, can look a lot like delirium. As we’ve emphasized so often in our Alula posts, this is yet another reason why it is so important to know the person — not just the “patient” — who is receiving care.

Sundowning tends to be patterned: caregivers see it as part of the chronic experience of their loved one’s dementia. It is often rhythmic and somewhat (though rarely perfectly) predictable. Delirium is different: it is aberrant and discordant from an established norm, even if that norm is itself abnormal.

With delirium, the most revealing phrase that doctors and nurses can hear a caregiver say is: “This is <u>not</u> like him.” Even when he’s sundowning.

We must know the person living with dementia. And we must know the person experiencing delirium.

A simpler way to remember it:

• Delirium changes the person quickly. Dementia changes the baseline slowly.
• Delirium comes and goes. Dementia usually has a steadier arc.
• Delirium often disrupts attention. Dementia may affect memory, language, judgment, or daily function over time.
• The family clue is the sentence: “This is not like him.”
• The practical implication is different: delirium asks us to look for a trigger; dementia asks us to understand a longer pattern.

Why is delirium dangerous?

Why is it important to recognize delirium when it’s present? Because unfortunately, it is very dangerous.

Delirium’s effects are not just transient. In the longer term, even if delirium resolves, it often leads to worsening cognitive and physical function. Those without pre-existing cognitive impairment who develop delirium are at increased risk of subsequently developing dementia. Those who have dementia and experience superimposed delirium may see their dementia advance in a more rapid manner.

This is why we should never wave away sudden, abnormal confusion as “just dementia.”

What should a family do when an older adult is suddenly confused?

Delirium doesn’t just happen. It is caused by something else.

As for Mr. Smith, the list of potential causes was lengthy, and more often than not, there are several causes coming together at once to precipitate delirium. These can range from serious infections and worsening heart conditions, to seemingly milder causes like dehydration, or even constipation. Risky medications too often play a role (We geriatricians often underscore: avoid potentially deliriogenic medications!).

Our recognition of delirium should immediately catalyze a search for possible causes. This is why we sent Mr. Smith to the ER. Given his recent critical illness and surgery, he needed the full scope of diagnostic technologies, and quickly.

So how should we interpret confusion in a loved one? Remember the triad of delirium: acute change, notable difficulty with attention, and waxing and waning. This often occurs in the context of a new stress to the bodily system — infection, surgeries, injuries, or novel medications, but also even sleep deprivation or inadequate nutrition.

In a future post, I will explore how we can best care for someone with delirium, in the moment. But great care depends first on accurate recognition.