Visual halluzinations in patients with PD and the Charles-Bonnet-syndrome - a phenomenological and pathogenetic confrontation

Visual hallucinations (VH) are seen in about a third of all patients with Parkinson's disease (PD) and are usually considered to be an early marker or clinical component of a dopaminergic psychosis. Their peculiar phenomenology has not yet been studied in a systematic manner. Methods: A semi-structured interview was performed twice in 62 PD patients. Different motoric and cognitive disease scales were used. The patients were not demented or depressed and had no other psychotic features other than hallucinations. Their visions was at least 0.6. Results: 22 patients (36 %) reported complex visual hallucinations or illusions in both interviews. These patients were not different from the non-hallucinating patients in terms of age, duration and stage of the disease, dosage and type of medication and frequency of cataracts. VH were diurnal in 41 % of the patients, nocturnal in 18 % of the patients and mixed in 41 patients. They were seen at least once weekly in 67 % and they lasted always less than an hour. VH most frequently involved adults, children and pets. They were often mobile and had normal size and physiognomy. Notable emotional reactions were only reported by 18 % of the patients. Discussion: The phenomenology of VH in PD differs from VH in exogenous or endogenous psychoses, but is similar to the Charles Bonnet-syndrome (CBS), appearing in elderly patients with different visual deficits. As PD patients suffer regularly from visual deficits of contrast and color perception, a similar pathogenesis to CBS can be hypothesized, with these "minor" and benign VH being due to "release phenomena" in relation to partial visual deprivation. The lack of multimodality hallucinations and of secondary paranoia as well as the clear sensorium are helpful features in distinguishing them from toxic psychosis.