The Charles Bonnet syndrome is characterized by the occurrence of visual hallucinations in elderly people, but without any mental disorders. Two clinical cases are described. An etiological and physiopathological theory is proposed, based on vascular pathology, lack of visual stimulation and a psychodynamic component.

We present two cases of Charles Bonnet syndrome in comorbidity with Parkinson’s disease. Patients developed visual hallucinosis before starting any antiparkisonian treatment. We briefly discuss the possible physiopathological mechanisms involving low visual acuity and Parkinson’s disease with visual hallucinosis.

Background: The Charles Bonnet syndrome (CBS) is characterized by distinct visual hallucinations and ocularpathology causing visual impairment in patients with insight and the absence of psychiatric comorbidity. The number of reported cases of CBS is expanding as the population ages and the prevalence of vision disorders increases. Antipsychotic medications are often prescribed. However, their efficacy in CBS has been based on sketchy evidence. The use of serotonin selective reuptake inhibitor (SSRI) for CBS was anecdotally reported. We herein describe effectiveness of escitalopram in a series of patients suffering from CBS who were unresponsive to antipsychotic treatment.

Methods: Eight consecutive patients suffering from CBS who did not respond to standard antipsychotic treatment were switched to escitalopram. CBS severity prior to escitalopram treatment was quantified using the Clinical Global Impression (CGI) scale and again after eight weeks of treatment. All had undergone brain CT and cognitive assessment. Brain CT imaging was normal except for an incidental finding of a small frontal meningioma in one patient. All had Mini-Mental Status Examination scores of ≥ 27/30.

Results: There were four men and four women, with a mean age of 81.7 ± 7.3 years. Previous antipsychotic treatment was mostly with risperidone, 1.0 to 3.0 mg/daily. Mean CGI-severity upon switching to escitalopram treatment was 5.7. This was significantly reduced to 1.8 (p < 0.001) after eight weeks of escitalopram treatment (mean dose: 11.8 mg/daily). There were no side effects, nor any adverse events were reported.

Conclusions: This is the first case-series to show that SSRI is an effective and well-tolerated treatment for visual hallucinations associated with vision impairment such as in CBS.

Based on recent insight into the thalamocortical system and its role in perception and conscious experience, a unified pathophysiological framework for hallucinations in neurological and psychiatric conditions is proposed, which integrates previously unrelated neurobiological and psychological findings. Gamma-frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in networks of thalamocortical circuits, thereby transiently forming assemblies of coherent gamma oscillations under constraints of afferent sensory input and prefrontal attentional mechanisms. If perception is based on synchronisation of intrinsic gamma activity in the thalamocortical system, then sensory input to specific thalamic nuclei may merely play a constraining role. Hallucinations can be regarded as underconstrained perceptions that arise when the impact of sensory input on activation of thalamocortical circuits and synchronisation of thalamocortical gamma activity is reduced. In conditions that are accompanied by hallucinations, factors such as cortical hyperexcitability, cortical attentional mechanisms, hyperarousal, increased noise in specific thalamic nuclei, and random sensory input to specific thalamic nuclei may, to a varying degree, contribute to underconstrained activation of thalamocortical circuits. The reticular thalamic nucleus plays an important role in suppressing random activity of relay cells in specific thalamic nuclei, and its dysfunction may be implicated in the biological vulnerability to hallucinations in schizophrenia. Combined with general activation during cholinergic arousal, this leads to excessive disinhibition in specific thalamic nuclei, which may allow cortical attentional mechanisms to recruit thalamic relay cells into resonant assemblies of gamma oscillations, regardless of their actual sensory input, thereby producing an underconstrained perceptual experience.

A case of musical hallucinosis is presented, which failed to respond to neuroleptics but responded to carbamazepine. Parallels with the Charles Bonnet syndrome are discussed.