What is the diagnosis and treatment for a 65-year-old female presenting with delusions of theft, paranoia about her husband's fidelity, and thought broadcasting, with potential differential diagnoses including delusional disorder, paranoid personality disorder, and cognitive disorders such as dementia?

Diagnosis: Late-Onset Delusional Disorder (Paranoid Type) with Thought Broadcasting

This 65-year-old woman most likely has late-onset delusional disorder (paranoid type) with thought broadcasting, though frontotemporal dementia and dementia with Lewy bodies must be systematically excluded before finalizing this diagnosis. 1, 2

Immediate Diagnostic Priorities

Rule Out Delirium First (Medical Emergency)

• Assess consciousness level and fluctuation immediately - if consciousness is impaired or symptoms fluctuate within hours/days, this is delirium until proven otherwise, which doubles mortality if missed 2, 3
• Ask specifically: When did confusion start? Are there lucid intervals during the day when she seems more alert? Does her mental state vary substantially throughout the day? 3
• Hypoactive delirium is the most commonly missed subtype in elderly patients and may present with nighttime confusion mistakenly attributed to baseline personality 3
• If delirium is present, immediately evaluate for life-threatening causes: infection, metabolic derangements, medication toxicity, stroke, or other acute medical illness 2, 4

If Consciousness is Intact: Proceed with Neurodegenerative Workup

• Visual hallucinations strongly favor medical causes (dementia with Lewy bodies, delirium, Charles Bonnet syndrome) over primary psychiatric disorder 2
• Dementia with Lewy bodies presents with recurrent visual hallucinations in up to 80% of patients as a core diagnostic criterion 2
• Frontotemporal dementia (behavioral variant) can present with prominent delusions and paranoia, particularly in C9orf72 carriers (21-56% have delusions/hallucinations) 1, 2, 5

Key Differentiating Clinical Features

Features Suggesting Delusional Disorder (Primary Psychiatric)

• Emotional distress and concern about symptoms - patients with primary psychiatric disorders typically show subjective distress, whereas frontotemporal dementia patients show emotional blunting 1
• Preservation of personality and thought processes outside the delusional system 6
• Normal appearance and behavior consistent with the delusion 6
• Delusions concern experiences that could conceivably occur in real life (being stolen from, infidelity) 6
• Age at onset in middle to late adulthood is typical for delusional disorder 6

Features Suggesting Frontotemporal Dementia

• Marked lack of insight and absence of emotional distress - patients with behavioral variant frontotemporal dementia show prominent emotional blunting and lower than expected subjective distress 1
• Progressive behavioral changes with personality deterioration beyond the delusional content 1, 5
• Who initiated the consultation? In frontotemporal dementia, family typically brings the patient; the patient rarely seeks help themselves 1
• Apathy, disinhibition, and compulsive behaviors accompanying the delusions 1

Features Suggesting Dementia with Lewy Bodies

• Recurrent, well-formed visual hallucinations (not just delusions) 2
• Fluctuating cognition with pronounced variations in attention and alertness 2
• Parkinsonian motor features 2
• Delusional jealousy (infidelity delusions) occurs in 26.3% of dementia with Lewy bodies patients versus only 5.5% in Alzheimer's disease 7

Essential Diagnostic Workup

Psychiatric Assessment

• Apply DSM-5 criteria rigorously to identify specific psychiatric diagnoses - many suspected frontotemporal dementia cases do not actually fulfill formal DSM-5 criteria for another mental disorder 1
• Assess for depressive symptoms systematically using clinician-rated scales (MADRS, HAM-D) - depression with psychotic features can present with delusions, but patients typically show depressed mood and suicidal thoughts 1
• Evaluate degree of insight - marked lack of insight is especially common in frontotemporal dementia, more so than primary psychiatric disorders 1
• Document whether patient is over- or under-emphasizing disability severity 1

Neurological Assessment

• Brain MRI is mandatory to detect frontotemporal atrophy (bilateral frontal/temporal lobe atrophy, often asymmetric) or other structural pathology 5
• Neuropsychological testing to assess for progressive cognitive decline beyond the delusional content 1
• Screen for concurrent serious physical diseases - delusional jealousy in dementia is preceded by onset of serious physical diseases in nearly half of patients 7

Medical Workup

• Complete metabolic panel, thyroid function, B12, RPR/VDRL to exclude reversible causes 1
• Medication review for anticholinergic burden and cognitively impairing medications 1
• Assess for alcohol use (delirium tremens can present with delusions, autonomic hyperactivity, and fluctuating symptoms) 4

Treatment Approach

If Delusional Disorder is Confirmed (After Excluding Delirium and Dementia)

• Antipsychotic medication is first-line pharmacotherapy for delusional disorder 6
• Start with low-dose atypical antipsychotic (risperidone 0.5-2 mg daily or equivalent) 6
• Hospitalization may be necessary if patient poses risk to self or others, or if outpatient management fails 6
• Psychotherapy has limited role due to lack of insight, but supportive approaches preventing rough awareness of deficits may help 8

If Frontotemporal Dementia is Diagnosed

• Atypical antipsychotics for neurobehavioral symptoms (trials ongoing but suggest some efficacy) 5
• Management focuses on behavioral symptoms rather than cure 5

If Dementia with Lewy Bodies is Diagnosed

• Extreme caution with antipsychotics - this population has severe sensitivity to antipsychotic medications 2
• Consider cholinesterase inhibitors as first-line for psychotic symptoms 2

Critical Pitfalls to Avoid

• Never start antipsychotics before ruling out delirium and medical causes - this masks the underlying process and exposes patients to serious medication risks 2
• Never use antipsychotics in dementia-related psychosis without informed consent about mortality risk - elderly patients with dementia-related psychosis treated with antipsychotics have 1.6-1.7 times increased risk of death compared to placebo 9
• Do not attribute new-onset paranoia in elderly patients to "just personality" without complete medical workup - this can miss frontotemporal dementia, dementia with Lewy bodies, or life-threatening delirium 2, 5
• Do not dismiss the complaint as "normal aging paranoia" - up to 46% of patients presenting with psychiatric symptoms have an underlying medical disease that is causative or exacerbating 2

Prognosis

• If delusional disorder: chronic course with variable outcome; successful management is difficult 6
• If dementia-related: delusional jealousy in dementia resolves within 12 months after treatment in 83% of patients, suggesting relatively benign prognosis 7
• If frontotemporal dementia: progressive decline in cortical functioning with behavioral deterioration 5