Alzheimer’s disease (AD) is a progressive neurological disorder that slowly causes brain cells to degenerate and die, leading to a decline in memory and thinking skills. While hallucinations are a type of behavioral and psychological symptom that can occur in AD, they are not considered a universal or defining feature of the disease. These sensory disturbances tend to emerge in the moderate to severe stages of the disease progression, often alongside other behavioral changes. When hallucinations do occur, they are generally less common than other symptoms like agitation or delusions.
Hallucinations and Alzheimer’s Disease: Clarifying the Connection
Hallucinations in the context of Alzheimer’s disease are a manifestation of the underlying neuropathology. The prevalence of hallucinations in AD is significantly lower than in other dementias like Lewy Body Dementia (LBD). In LBD, visual hallucinations are a core, early symptom, occurring in over 50% of cases.
The hallucinations experienced by individuals with AD are predominantly visual, although auditory, tactile, and olfactory experiences can also occur. Visual hallucinations often involve seeing people, animals, or complex situations that are not actually present. Research suggests that AD patients who experience visual hallucinations may have greater neuropathology in the occipital lobe, the region of the brain dedicated to visual processing.
The onset of visual hallucinations in AD tends to be much later in the disease course compared to LBD, where they often appear within the first five years of the dementia. When hallucinations do appear in AD, they are sometimes associated with a greater overall cognitive impairment and a more rapid decline. The presence of hallucinations in an AD patient may also be a clinical signal of an overlap with Lewy body pathology, meaning the brain is affected by both AD and LBD changes.
Understanding the Difference Between Hallucinations and Delusions
Hallucinations and delusions describe two distinct types of sensory and cognitive disturbances in dementia. A hallucination is defined as a sensory perception experienced without an external stimulus. The person genuinely sees, hears, smells, tastes, or feels something that is not physically there.
For instance, an individual might see children playing in the living room or feel insects crawling on their skin, even though the room is empty or their skin is clear. After the event, the person may sometimes recognize that the experience was not real, particularly if the hallucination was not frightening.
Delusions, by contrast, are fixed, false beliefs that are not based in reality and cannot be changed by logical reasoning or evidence. Delusions are more common in Alzheimer’s disease than hallucinations, occurring in almost half of all dementia patients. These false beliefs often take the form of paranoia or suspicion, stemming from memory loss and confusion.
Common examples of delusions include the belief that caregivers are stealing money or possessions, or that a spouse is being unfaithful. The person may also believe that uninvited people are living in their home or that their food is being poisoned. Unlike a hallucination, a delusion is an unshakable idea that the person accepts as complete truth, making it impossible to reason with them about the belief.
Assessing Triggers: When the Cause Is Not Alzheimer’s
The sudden onset or a noticeable increase in hallucinations or delusions should prompt an immediate medical assessment. An acute change in behavior or cognition is often a sign of delirium, which requires urgent attention. Delirium is a state of severe confusion that can include hallucinations, and it is frequently triggered by an underlying, treatable medical condition.
A common non-AD trigger is a Urinary Tract Infection (UTI) or other systemic infections like pneumonia, which cause inflammation that interferes with normal brain function. Acute physical problems, such as dehydration, fever, or intense, unaddressed pain, can also lead to the sudden appearance of psychotic symptoms.
Furthermore, medications are a very frequent cause of new or worsening hallucinations and delusions in older adults. Adverse reactions or interactions from new prescriptions, over-the-counter drugs, or even existing medications can all trigger these symptoms. Even medications used to treat Parkinson’s disease can sometimes provoke hallucinations.
Environmental and sensory factors should also be considered as potential triggers, which can cause illusions or misidentification that are mistaken for true hallucinations. Poor lighting, confusing shadows, excessive background noise, or uncorrected vision and hearing impairments can all contribute to a person misinterpreting their surroundings. Having a medical professional rule out these secondary, treatable causes is the most important first step when any new behavioral symptoms appear.