Psychosis is a severe but relatively rare behavioral/neuropsychiatric symptom in Huntington's disease (HD). Psychosis in HD is defined by the presence of delusions or hallucinations. Delusions are fixed beliefs not grounded in reality. Hallucinations are the sensory experience of seeing, hearing, or feeling something not based in realtiy.
Psychosis in HD: The published information on psychosis in HD is relatively small, and those studies available are hard to compare. These reports have estimated in the range of 3% to 11% of individuals with HD will have psychotic symptoms. The lower numbers come from studies of outpatients that may include motor premanifest individuals enrolled in observational trials. Higher numbers have been reported for those in long term care facilities. Because individuals with HD are often on antipsychotic medications for other symptoms like chorea or irritability, it may be that milder psychosis is not apparent (so not diagnosed) because it has been (pre) treated. Though not occuring as often as many other symptoms in HD, psychosis is a severe symptom with major impact on families and individuals. When psychosis occurs it is probably the behavioral symptom that presents highest caregiver burden, and can often result in institutionalization.
Not all psychosis in an individual with HD is due to the disease. For instance an individual with the HD mutation could also have schizophrenia or other psychiatric disorder underlying psychosis. This may be the case (or not) when a gene carrying individual develps pyschosis before the occurance of other HD symptoms. Though it has not been defined in HD, when psychosis occurs in an individual with Parkinson's disease before motor diagnosis, it is not considered part of the disease. For instance, it would be hard to know the underlying cause of psychosis if an HD mutation carrier might have a mother with HD and father with schizophrenia who developed psychosis. In terms of treating paychosis, it really doesn't make any difference whether due to HD or other psychiatric disorder.
Delusions are reported to be more common than hallucinations in HD. Either or both of these symptoms may occur at any stage of disease, but most experts believe it is more common in later stages. It would make sense that in later stages when cognitive impairment is greater, there would be more difficulty in accurately perceiving reality.
A delusion example: At least in some individuals with psychosis, earlier milder symptoms may present before progressing to psychosis. A woman in long term care with fairly advanced Huntington's disease might obsessively worry about her clothes. She was treated for this perseverative/obsessional behavior and managed for more than a year. She subsequently became agitated when she could not find clothes when they were being laundered by staff, and became delusional with the false belief that her clothes were being stolen. And though she has been treated with an antipsychotic drug, this delusion persists. Like her, there are some individuals with HD whose psychotic symptoms are managed, but do not disappear with antipsychotic drug treatment.
A hallucination example: A very talkative pleasant out-patient began with disorganized speech, going from one thought to another until being brought back to the topic of the conversation. He subsequently was admitted to a long term care facility where on the same night a wind storm toppled a large tree just outside his room. The following morning he was frightened by the noise and commotion when workmen removed the tree. Subsequently on the following days he "saw" men that he believed were coming to harm him. This hallucination symptom went away when treated with an antipsychotic. Six months later when dosage of antipsychotic was decreased, milder but still distressing symptoms recurred, then disappeared when former dosage was used. Like him, there are some individuals with HD who have symptoms return when dosages are decreased. In this individual, another later attempt to reduce dosage was successful. Attempts at reducing dosage is important because antipsychotic drugs have side effects that can be harmful to those with HD.
Stress as a possible driver towards psychosis: Though there has been no study to support this, both of these examples suggest that stress can be a driver towards psychosis, and/or increase the severity of these symptoms. Both are also examples of altered perception of real events such as missing clothes led to worry, then belief that clothes were stolen, and strangers with saws removing trees led to the belief that these workmen meant him harm.
Psychosis treatment: If symptoms can not be managed by providing a calm environment, an antipsychotic is the drug of choice. And it may take a while (weeks) for these drugs to be fully effective. In very severe treatment-resistent individuals whose behavior can not be adequately managed with standard dosing of antipsychotic drugs, a psychiatrist, best if experience in HD should be consulted.
Why try to decrease dosage when the symptom is controlled? The simple answer is that antipsychotic drugs have unwanted side-effects. Though the older antipsychotics may be more likely to do this more than the newer ones, all of them interfere and slow down voluntary movements that can make it harder to walk, to coordiante hand movements, and to swallow. Experts recommend trying to decrease dosage only after at least 6 monts to a year after symptoms are managed. Too often individuals with HD will stay on the high dosages of these drugs (without attempting a taper) the rest of their lives.
Summary: Though psychosis is a severe symptom of Huntington's having major detrimental impact on the indiviudal with HD and families, this psychiatric symptom can be managed with medications. While I don't believe psychotic symptoms can be prevented, I do believe there is value in providing information that may help in the earlier recognition and treatment of this symptom.