Portal de Periódicos da CAPES

Charles Bonnet Syndrome

1996; Wiley; Volume: 44; Issue: 9 Linguagem: Inglês

10.1111/j.1532-5415.1996.tb02955.x

1532-5415

Ronald F. Pfeiffer, Iván Bódis-Wollner,

Neurology and Historical Studies

In our more whimsical moments it is just possible that many of us have entertained a secret wish to develop the Charles Bonnet syndrome (CBS). The idea of being able to experience vivid, complex, pleasant visual hallucinations (perhaps including Lilliputian figures) as if one were “watching a movie with no sound”1 while the sensorium and insight remain entirely clear has an undeniable appeal, if only as a means of escape from tedious or unpleasant situations. However, Pliskin and colleagues in their article in this issue2 bring us back to reality by convincingly suggesting that there is a price to pay for such experiences. The precise definition of CBS has undergone remodeling since its original introduction into medical terminology by de Morsier in 1938.3 Whereas the initial description was of visual hallucinations occurring in an older individual with visual impairment (Charles Bonnet's grandfather), subsequent investigators have reported individuals with similar hallucinations in whom no visual impairment was evident, suggesting that visual impairment is not an integral part of the clinical syndrome. De Morsier himself, in his 1967 review of the syndrome he had previously named, came to the conclusion that impaired vision caused by ocular pathology was not present in every individual with CBS and thus, not a necessary part of its definition.,4,5 Gold and Rabins, in their formulation of diagnostic criteria for CBS, make a specific point to neither include nor exclude visual system pathology as part of CBS.5 In the experience of Teunisse and colleagues, bilateral visual impairment was present in the great majority of individuals with CBS, but they also noted this was not invariably so.6 In a subsequent study examining the frequency of CBS in visually handicapped compared with visually intact individuals, Teunisse et al. found an 11% occurrence of CBS in the visually impaired but only a 1% occurrence in those with intact vision.7 They suggested that bilateral impairment of visual acuity, regardless of its etiology, is a predisposing factor in CBS though not its sole cause. The experience of Plisken and colleagues echoes and expands upon these findings. All 14 of their subjects had ocular pathology. Bilateral severe visual acuity impairment was not evident in each individual; in fact, visual acuity was 20/40 or better in at least one eye in 9 of the 14. In additional visual system evaluation, they found that 75% of individuals tested displayed abnormal visual evoked potentials, further implicating visual system involvement but not localizing the site of the abnormality. Thus, Plisken et al. come full circle and suggest that the presence of ocular pathology be reinserted into the list of diagnostic criteria for CBS. While the preponderance of evidence does, indeed, suggest that visual system involvement is inextricably entwined in the essence of CBS, perhaps their focus on ocular pathology is too narrow. Cogan8 and others9 have proposed that visual hallucinations in the visually impaired are release phenomena, or the result of deafferentation, analogous to phantom limb experiences. Chatterjee and Southwood discuss the controversy about the neural basis for visual imagery in a recent review and provide evidence that regions in the visual association cortex are responsible for this activity.10 Dysfunction in these regions, whether it is structural or functional and whether it is the result of primary excitation, release of inhibition, or disrupted reentry signals, could produce unwanted as well as wanted images, whether or not primary ocular pathology is present. Further study, perhaps including functional neuroimaging procedures, may shed additional light on this aspect of CBS. The more central assertion by Plisken and colleagues is that CBS is characterized by the presence of cognitive impairment and that isolated visual hallucinations, as seen in CBS, may be an early sign of dementia. In the literature discussing CBS, the point has been made repeatedly that cognitive function is completely intact in this syndrome. Neither Gold and Rabins5 nor Teunisse and colleagues6 include cognitive impairment in their clinical characterization of CBS, although it is of more than passing interest that 12 of the 14 individuals studied by Teunisse et al. had some evidence of CNS dysfunction of various etiologies. See also p 1055 The present study by Plisken and colleagues presents the most thorough and detailed evaluation of cognitive function in CBS and clearly demonstrates the presence of cognitive impairment, albeit mild, in these individuals. It is probable that previous investigators did not pick up the cognitive impairment because virtually all studies (that of Schultz and Melzack11 might be considered a partial exception) utilized only screening test measures such as the Mini-Mental State Examination, which, as Plisken et al. correctly point out, is not sensitive to the early stages of dementia. The fact that individuals who had lost insight into the reality of the hallucinations (one might argue that these individuals no longer meet the strict definition of CBS) had more severe cognitive impairment provides additional support for the assertion of cognitive impairment, perhaps of a progressive character, in CBS. While other investigators suggest that the term, “Charles Bonnet plus” be utilized when cognitive impairment is present,12 the data of Plisken et al. suggest there is no need for such a term because some degree of neuropsychological impairment is present in all individuals with CBS. We anticipate that this may be a controversial assertion, but it is one that is certainly amenable to confirmation or refutation. To the neurologist who deals frequently with movement disorders, the features of CBS appear to parallel closely the hallucinations that can be seen most commonly during carbidopa/levodopa therapy in Parkinson's disease (PD). In these patients, the hallucinations are almost always visual, consisting of complex, nonthreatening images such as children or even entire families of people, and often (at least initially) occur with preserved insight. Some element of cognitive impairment is usual for individuals with PD who develop levodopa-induced hallucinosis. To our knowledge, vision has never been tested specifically in PD patients who experience hallucinations although impairment of visual contrast sensitivity, retinograms, and visual evoked potentials has clearly been described in PD.13 Since the neuropharmacology of CBS is entirely unknown, the similarities to levodopa-induced hallucinosis are of potential interest, although neuroleptics are only of inconsistent benefit in CBS.14 Since ondansetron, a serotonin 5-HT3 antagonist, has been reported to be effective in ameliorating levodopa-induced hallucinosis in PD,15 it would be interesting to examine its efficacy in CBS. The data presented by Plisken and colleagues indicate that CBS may not be the benign curiosity it has heretofore been considered but rather the harbinger of serious neurological disease. If this is so, development of CBS should prompt a thorough evaluation searching for treatable causes of dementia and ocular pathology. Early recognition of primary neurodegenerative dementing processes, such as Alzheimer's disease, may also become vitally important if neuroprotective therapy of these processes emerges as a viable treatment modality.