Alzheimer’s disease (AD) is a progressive neurodegenerative disorder primarily known for its impact on memory and overall cognitive function. While the condition is most often associated with memory loss and confusion, the effects extend to a wide range of behavioral and psychological symptoms. Hallucinations can occur in AD, but they are not typically among the most common or earliest signs of the disease. Understanding these symptoms requires distinguishing them from similar experiences and knowing when they are most likely to manifest.
Hallucinations Versus Delusions
Psychotic symptoms are a common feature across various types of dementia, and it is important to differentiate between hallucinations and delusions. A hallucination is a false perception involving one of the five senses, such as seeing or hearing something that is not actually present. For people with AD, visual hallucinations are the most frequently reported type, where the person might see people, animals, or objects that others cannot.
Conversely, a delusion is a fixed, false belief not based on reality that cannot be changed by logical reasoning or evidence. Although both are classified as psychotic symptoms, studies indicate that delusions are significantly more common in individuals with Alzheimer’s disease than true hallucinations.
Frequency and Timing in Alzheimer’s Disease
Hallucinations are relatively uncommon in the mild, or early, stages of Alzheimer’s disease, which is typically characterized by memory impairment. The overall prevalence of hallucinations in AD can vary widely across studies, but is generally reported to affect only a small percentage of patients in the early phase. These sensory disturbances are more likely to appear later as the disease advances into the moderate to severe stages.
In the more advanced stages, the frequency of hallucinations increases, with some research suggesting a median prevalence around 23% in AD populations. Their appearance is often linked to increased cognitive decline and longer duration of the illness. External factors such as poor vision, infections, delirium, or certain medication side effects can also trigger or worsen the appearance of hallucinations at any stage.
Distinguishing Symptoms from Other Dementias
When a person with cognitive decline experiences frequent hallucinations, it often prompts a medical evaluation to determine if the diagnosis is purely Alzheimer’s disease or another form of dementia. While hallucinations are a possible feature of late-stage AD, they are a core and often early feature of Lewy Body Dementia (LBD). LBD is the second most common form of neurodegenerative dementia, and its diagnosis is strongly supported by the presence of recurrent visual hallucinations.
The visual hallucinations in LBD are typically described as vivid, detailed, and recurring, often involving people or animals. In contrast, AD-related hallucinations are generally less common and tend to occur much later in the disease course. The presence of frequent visual hallucinations early on is therefore a strong differentiating factor used by clinicians to help distinguish LBD from typical Alzheimer’s disease. This distinction is important because LBD and AD may respond differently to certain dementia medications.