What mental health conditions can cause hallucinations in patients, particularly in geriatric individuals?

Mental Health Conditions That Cause Hallucinations

Hallucinations occur across multiple psychiatric diagnoses without being pathognomonic to any single disorder, but the specific pattern, modality, and clinical context—particularly in geriatric patients—determines whether they represent primary psychiatric illness, delirium, or neurodegenerative disease. 1

Primary Psychiatric Disorders

Schizophrenia Spectrum Disorders

• Schizophrenia is characterized by auditory and visual hallucinations as cardinal features, with auditory hallucinations being most common 1, 2
• Schizoaffective disorder presents with hallucinations at rates similar to schizophrenia initially, though longitudinally schizophrenia patients demonstrate higher persistence of both auditory and visual hallucinations over 20-year follow-up 3
• Tactile, olfactory, and gustatory hallucinations occur in approximately 20% of schizophrenia patients, though these are less common than auditory or visual modalities 4
• Critical distinction: Consciousness and awareness remain intact in primary psychotic disorders, unlike delirium 1

Mood Disorders with Psychotic Features

• Bipolar disorder can present with hallucinations, particularly during manic or mixed episodes 1
• Depression with psychotic features includes hallucinations as a defining characteristic when psychosis is present 1
• Bipolar and unipolar depression patients show significantly lower rates of hallucinations compared to schizophrenia spectrum disorders, both at initial presentation and over longitudinal course 3
• Late-onset bipolar disorder type 1 has specific associations with GRN mutations that may evolve into behavioral variant frontotemporal dementia 1

Other Psychiatric Conditions

• Borderline personality disorder can present with transient hallucinations, particularly auditory hallucinations, without meeting criteria for a psychotic disorder 5
• Post-traumatic stress disorder (PTSD) may include hallucinations related to trauma content 5
• Persistent auditory hallucinations alone, without other psychotic symptoms and with preserved reality-testing, do not necessarily indicate a psychotic disorder and should not automatically trigger antipsychotic treatment 5

Delirium: The Critical Differential in Geriatric Patients

In elderly patients presenting with new-onset hallucinations, delirium must be considered a medical emergency until proven otherwise, as missing this diagnosis doubles mortality. 6, 7

Distinguishing Features of Delirium

• Fluctuating course with intermittent symptoms and lucid intervals is pathognomonic for delirium, not primary psychosis 6, 7
• Impaired consciousness and confusion distinguish delirium from psychosis where consciousness remains intact 1, 6
• Visual hallucinations are the strongest indicator of underlying medical cause rather than primary psychiatric disorder 6, 7
• Olfactory hallucinations are extremely rare in primary psychosis and should immediately trigger investigation for neurological causes 6, 7

Common Precipitating Causes

• Infections (urinary tract infections and pneumonia are most common) 1
• Medications, particularly anticholinergic agents 6
• Over-the-counter combinations of pseudoephedrine, dextromethorphan, and caffeine can cause psychosis and hallucinations in elderly patients 6
• Metabolic derangements, toxin exposure, or substance withdrawal 1
• Two or more coexisting precipitating causes frequently occur together 1

Neurodegenerative Disorders in Geriatric Populations

Dementia with Lewy Bodies (DLB)

• Recurrent visual hallucinations occur in up to 80% of DLB patients and form one of the core diagnostic criteria 1
• Visual hallucinations in DLB are typically well-formed, detailed, and may include people or animals 1
• Hallucinations can be assessed for both frequency and severity, with severity having greater clinical relevance for treatment trials 1

Behavioral Variant Frontotemporal Dementia (bvFTD)

• C9orf72 repeat expansion carriers present with delusions and hallucinations (mostly auditory) in 21-56% of cases 1
• Psychiatric symptoms including bipolar disorder, obsessive-compulsive disorder, and schizophrenia-like presentations can precede classic bvFTD symptoms by up to a decade 1
• GRN mutations cause visual hallucinations and delusions in up to 25% of patients, which can be the presenting symptom 1
• Severe psychotic symptoms in apparent late-onset psychiatric illness should prompt consideration of C9orf72 screening, even without family history 1
• Prevalence of psychotic disorders due to general medical conditions is higher in those 65 years or older 1

Parkinson's Disease and Related Disorders

• Visual hallucinations occur commonly in Parkinson's disease, particularly in advanced stages or with dementia 1
• Hallucinations in Parkinson's disease can be assessed using scales that capture both frequency and severity 1

Charles Bonnet Syndrome

• Occurs in patients with any level of vision impairment (reduced acuity, contrast sensitivity, or visual field loss) 1
• Characterized by recurrent, vivid visual hallucinations with intact insight that what is seen is not real 1
• No other neurological or medical diagnosis explains the hallucinations 1
• Prevalence ranges from 15-60% among patients with ophthalmologic disorders 1
• Attributed to cortical-release phenomena from lack of afferent visual information 1
• Atypical features requiring medical evaluation: lack of insight despite explanation, images that interact with the patient, or associated neurological signs 1

Secondary Medical Causes of Psychosis

The American College of Radiology guidelines emphasize that secondary causes of psychosis are directly related to underlying medical conditions and must be systematically excluded 1:

• Endocrine disorders (thyroid dysfunction, Cushing's syndrome)
• Autoimmune diseases (systemic lupus erythematosus, anti-NMDA receptor encephalitis)
• Neoplasms and paraneoplastic processes
• Neurological disorders (stroke, seizures, multiple sclerosis)
• Infections (CNS infections, HIV, neurosyphilis)
• Genetic or metabolic disorders
• Nutritional deficiencies (B12, thiamine)
• Drug-related intoxication, withdrawal, side effects, and toxicity

Up to 46% of patients presenting with psychiatric symptoms have an underlying medical disease that is causative or exacerbating. 7

Critical Clinical Algorithm for Geriatric Patients

Step 1: Assess Level of Consciousness

• Impaired/fluctuating consciousness → Delirium until proven otherwise 6, 7
• Intact consciousness → Consider primary psychiatric disorder or neurodegenerative disease 1

Step 2: Characterize Hallucination Modality

• Visual hallucinations → Strongly favor medical cause (delirium, DLB, Charles Bonnet syndrome) 6, 7
• Olfactory hallucinations → Immediately investigate for neurological pathology 6, 7
• Auditory hallucinations alone → May occur in primary psychiatric disorders, but require complete medical workup in geriatric patients 5, 3

Step 3: Evaluate Temporal Pattern

• Fluctuating/intermittent with lucid intervals → Delirium 6, 7
• Persistent without fluctuation → Primary psychiatric disorder or neurodegenerative disease 1

Step 4: Complete Medical Workup Before Psychiatric Diagnosis

• Medication review (especially anticholinergics and over-the-counter combinations) 6
• Laboratory evaluation: CBC, CMP, urinalysis with culture, thyroid function 6
• Vital signs and examination for infection 6
• Neurological examination for focal deficits 6
• Consider neuroimaging if indicated by clinical presentation 1

Step 5: Consider Genetic Testing in Specific Scenarios

• Late-onset behavioral changes with prominent psychiatric symptoms and family history of neurodegeneration or late-onset psychiatric disorders warrant C9orf72 screening 1
• Severe psychotic symptoms disproportionate to other behavioral changes suggest possible genetic FTD 1

Critical Pitfalls to Avoid

• Never attribute new-onset hallucinations in elderly patients to "just depression with psychotic features" without complete medical workup, as this can miss life-threatening delirium 6, 7
• Do not start antipsychotics before ruling out delirium and medical causes, as this masks the underlying process and exposes patients to serious medication risks including increased mortality in dementia-related psychosis 6, 8
• Elderly patients with dementia-related psychosis treated with olanzapine are at increased risk of death compared to placebo, with higher incidence of cerebrovascular events 8
• Olfactory hallucinations should never be dismissed as "bizarre but benign" as they indicate serious neurological pathology 6, 7
• Visual hallucinations should not be automatically attributed to primary psychosis in any age group, as they strongly suggest medical etiology 6, 7
• No single hallucination feature uniquely indicates schizophrenia diagnosis (except age of onset in late adolescence); 95% of hallucination features in schizophrenia are shared with other psychiatric disorders 2