Psychosis in dementia or dementia in psychosis? A clinical approach to a common puzzle

A large national US study in Medicare patients has just shown that 27.9% of 66 year-olds with a diagnosis of schizophrenia also have a diagnosis of dementia.¹ This compares with a 1.3% rate of dementia among people of the same age without serious mental illness. By 80 years of age, the prevalence of dementia is 70.2% in people with schizophrenia and 11.3% in others.

At 66 years of age, the prevalence of dementia among people with schizophrenia is the same as that of 88 year olds without serious mental illness.

High rates of dementia among older schizophrenia patients will impact treatment and service use¹

Cognitive disorders can mimic psychosis

While some cases are vascular in origin, or Alzheimer’s disease, many elderly patients with schizophrenia have undifferentiated dementias, Dr Aga said.

The connection is also evident the other way round. Neurocognitive disorders are commonly associated with late-onset psychosis, and International Psychogeriatric Association criteria for their diagnosis in such disorders have recently been updated.² A third or more of patients with Alzheimer’s disease have psychotic symptoms at any given time.³

Even in their prodromal phase, neurocognitive disorders can mimic a primary psychiatric disorder, making differential diagnosis a major challenge, noted Dr Aga. 

There is a complex interface between aging, psychosis, and cognitive decline

Insights from experience

Dr Aga also made a number of other clinical observations about the diagnosis and management of geriatric mental health disorders:

• Late onset schizophrenia seems to be less related to a family history, suggesting lower genetic loading
• Agitated depression with psychotic features can be difficult to differentiate from late-onset schizophrenia. Both can present with cognitive impairment, psychotic features and depression. It is helpful to distinguish whether depression or psychosis came first. The presence of first-rank symptoms such as delusions of control suggests schizophrenia.
• Biomarkers can be helpful in the differential diagnosis of depression, psychosis and dementia. While obtaining CSF markers is invasive, and serum markers are not yet ready for routine use, MRI is accessible and informative. MRI should involve specific sequences and include volumetric analysis.
• In treating depression with psychosis, it is appropriate to start with antidepressants, with ECT a possibility – even in the presence of cognitive symptoms -- when there is high risk of suicide. Combining antidepressants with an antipsychotic can be helpful, with the latter used with caution in patients who are frail, and titrated from a low dose. Brain atrophy may make Transcranial Magnetic Stimulation less effective in treating depression in older adults.
• With agitation in AD dementia, the first question is whether it is psychotic in origin. If so, an antipsychotic is the first option. If not, the agitation  may respond well to an SSRI.^4,5
• Lewy Body dementia responds well to cognitive enhancers.