Psychosis in Huntington's disease: a review and comparison with schizophrenia.

Psychosis is a relatively rare phenomenon in Huntington's disease (HD) yet it occurs more commonly amongst individuals with HD than in the general population. Its presence is associated with significant distress and caregiver burden. This review evaluates the epidemiology, aetiology, phenomenology, neurobiology and treatment of psychosis in HD, drawing comparisons with schizophrenia as an archetypal psychotic disorder. We conducted a detailed literature search and narrative synthesis and found that prevalence estimates of psychosis in HD varied widely (4.1-17.6 %). While generally more common in those with established motor symptoms, psychosis occurred throughout the HD course. Its presence conferred a poorer prognosis, including greater functional and cognitive decline. No distinct phenomenology of psychosis in HD emerged; paranoid ideation was common whereas formal thought disorder was rarely reported. Like schizophrenia, psychosis in HD is associated with depression, suicidality, apathy, executive and social cognitive dysfunction. The neurobiology of psychosis in HD is not well understood however HD neurobiology shares some overlap with schizophrenia. Despite the absence of mesostriatal hyperdopaminergic transmission, frontostriatal network dysfunction, glutamatergic dysregulation and medium spiny neuron pathology could contribute to psychosis manifestation. The development of psychosis in HD is conceptualised within a stress-diathesis framework, involving an interaction between genetic risk (with some shared vulnerability to schizophrenia), neuronal changes and psychosocial stressors. Clinically, this implies a rationale for utilising therapeutic approaches trialled in schizophrenia, as there is no evidence that psychosis in HD requires fundamentally different treatment, except for an awareness of the antipsychotic effects on HD motor symptoms.