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 P arkinson's disease (PD) and are usually considered to be an early marker or clinical component of a dopaminergic psychosis. Their peculiar phenomenolo gy has not yet been studied in a systematic manner. Methods: A semi-structu red interview was performed twice in 62 PD patients. Different motoric and cognitive disease scales were used. The patients were not demented or depre ssed and had no other psychotic features other than hallucinations. Their v isions was at least 0.6. Results: 22 patients (36 %) reported complex visua l hallucinations or illusions in both interviews. These patients were not d ifferent from the non-hallucinating patients in terms of age, duration and stage of the disease, dosage and type of medication and frequency of catara cts. VH were diurnal in 41 % of the patients, nocturnal in 18 % of the pati ents 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 adult s, children and pets. They were often mobile and had normal size and physio gnomy. Notable emotional reactions were only reported by 18 % of the patien ts. 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 pati ents 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 d eprivation. The lack of multimodality hallucinations and of secondary paran oia as well as the clear sensorium are helpful features in distinguishing t hem from toxic psychosis.