Why do delusions and hallucinations occur in Parkinson’s disease

Parkinson’s disease is the second most common neurodegenerative disease, only preceded by Alzheimer’s disease. Thus, Parkinson’s disease affects 150,000 people in Spain and about 4 million people in the world. According to prevalence studies, 3% of the population over 60 years of age will suffer from Parkinson’s disease and 10% will be early onset forms (between 30 and 40 years of age).

Causes of Parkinson’s disease

Parkinson’s disease is caused by the loss of neurons in different regions of the brain, including the substantia nigra, which is one of the main sources of dopamine (important in motor function) in the brain. In addition, it is part of the basal ganglia, a group of structures that play an important role in voluntary movement and posture control, as well as a key role in mood regulation and certain cognitive processes such as attention and memory.

Psychotic symptoms in Parkinson’s, somewhat underestimated

Motor symptoms, such as tremor, slowness and rigidity, define Parkinson’s disease. However, although the “non-motor” complications associated with the disease are now recognized, they are often poorly understood or under-diagnosed. Thus, psychiatric or behavioral disturbances, cognitive impairment or sleep disorders are very common.

Moreover, distortions of reality, bizarre perceptions or exaggerated ideas are part of the psychotic symptomatology. This type of symptoms is highly variable among patients, but it is estimated to affect up to 60% of patients.

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The most common psychotic symptoms are visual hallucinations, although many patients also have tactile hallucinations (they think they have threads on their fingers) or auditory hallucinations (they hear noises or voices). These hallucinations can appear at any time during the disease and are divided into:

  • Minor hallucinations. They affect 30% of patients. They are divided into hallucinations or sensations of presence (noticing presences behind), passage hallucinations (seeing shapes or shadows that are difficult to recognize passing by the sides of the visual field), minimal visual distortions (seeing some objects change shape or move) and illusions (seeing shapes and faces recognizable as animals on non-regular surfaces).
  • Structured or complex hallucinations. They affect up to 25% of patients. They can be very real and present in the form of animals or people that, in many cases, the patient recognizes as a hallucination.

Minor hallucinations are known to evolve into structured hallucinations. Many patients initially have mild sensations of presences or see shapes that they cannot recognize but, over time, come to establish complex perceptual phenomena. During this process it is important to distinguish the ability to recognize the visions as hallucinations from the loss of consciousness.

On the other hand, delusional ideas encompass a series of distortions in thinking that are more frequent in patients with Parkinson’s disease progressing to significant cognitive impairment. Some of these ideas are that the patient believes that family members want to steal or hurt him, that his partner is cheating on him, that the people around him are impostors, or even that he no longer lives at home. Many of these symptoms may go unnoticed and unrecognized if patients are not asked about them. However, these symptoms are experienced with great incomprehension by the patient, which generates discomfort and anxiety in him, so it is important to make these symptoms known and thus help the patient.

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Why do psychotic symptoms occur in Parkinson’s disease?

The exact cause of this type of symptoms in Parkinson’s is not known. There are some factors such as age, the stage of the disease, taking certain drugs, the severity of the symptoms or having a psychiatric history that may be at risk.

In addition, the use of certain drugs is closely related.

  • Dopaminergic therapy. The most common drugs to treat Parkinson’s disease are those that increase dopamine levels, with the aim of improving the motor symptoms that appear as a consequence of low levels of this neurotransmitter. However, the increase in dopamine levels can lead to the development of psychotic symptoms.
  • Evolution of the disease. As the disease progresses, it can generate changes in the brain, unrelated to medication. These are related to worsening of cognitive abilities that, directly or indirectly, cause psychotic symptoms.

How to treat psychotic symptoms in Parkinson’s disease

It is common that there is a relationship between the medication taken by the patient and the symptomatology. Hence, dose adjustment is often the first option. Sometimes finding the balance between the correct dose of medication to alleviate motor and psychiatric symptoms is not easy.

If the neurologist is unable to reduce these symptoms by adjusting the medication, or if the severity of the symptoms is significant, antipsychotic drugs will be used. In any case, both the management and adjustment of the optimal doses of dopaminergic or antipsychotic medication should be stipulated by the specialist in the field.