Environmentally Dependent Delusions in Dementia

An 82-year-old man presented with a swollen penis. The patient had worsening right heart failure with dependent edema in his genital region. His history was significant for vascular dementia, hypertension, congestive heart failure, and diabetes mellitus.

His wife reported a gradual and progressive decline in his cognition and behavior for several years. During the prior 3 to 4 months, the patient had developed delusions. Coincident with the swelling of his penis, he became preoccupied with sex, believed that women wanted to have sex with him, and remained undressed from his waist down. When observing partially clothed children, he concluded that everyone around him was naked. When his wife changed her appearance, he decided that she was not his wife but an impostor. Upon a mention of his deceased brother, he elaborated a story that his brother was coming and he would wait for him at his door. The patient would hold these beliefs for hours or days.

On examination, he was attentive but extremely stimulus-bound. During the testing, he would name things that he saw or heard in his environment. Intrusions and perseverations impaired naming, verbal fluency, and most mental status tests. On a verbal learning task, 15-minute recall was 0/10 with numerous intrusions. His constructions were stimulus-bound and his graphomotor sequences were perseverative. He had genital, presacral, and lower-extremity edema. There were no cranial nerve or sensorimotor deficits, except for sensory loss in the lower extremities. His reflexes were normal except for bilateral grasp reflexes. Cranial CT imaging showed extensive deep white matter ischemic changes, especially in subfrontal regions.

After his heart failure resolved, he remained cognitively impaired and prone to delusions. On hearing a televangelist, he became convinced that he would receive a divine visitation. Individuals on television often seemed to him to persist in his hospital room. When an attractive nurse entered the room, he developed the belief that she was secretly in love with him and had known him for 10 years. His delusions partially responded to risperidone 1 mg bid.

We evaluated an unusual patient with multiple delusions triggered by environmental stimuli. The patient was stimulus-bound and showed intrusions and perseverations. His delusions appeared to correspond to “stuck-in-set” perseverations driven by salient stimuli in his environment.¹ Frontal lobe disease has produced an “environmental dependency syndrome” of severe stimulus-bound, perseverative behaviors usually manifest as a need to imitate others, use observed objects, or respond to environmental situations.²

A possible neurobiological mechanism for “environmentally dependent” delusions is dysfunction of the mirror neuron system.³ Prefrontal mirror neurons are activated during both observation and imitation of a behavior.⁴ They are also probably involved in the generation of related “resonance behaviors” in response to observed stimuli.⁵ Frontal microvascular disease could confabulate delusions through pathological overactivity of mirror neurons that program individuals to respond to environmental events.