Peduncular hallucinosis

Abstract

[Background and aims] The purpose of this paper is to clarify the clinical characteristics and pathomechanism of Peduncular Hallucinosis (PH). ?Methods] I analyzed 38 previously reported cases of PH in the literature, in which the lesions responsible for the PH were clarified. Representative cases of PH will be presented at the meeting. ?Results] The causal pathology of PH was classified into brain tumors (tumor; 12), brainstem infarction (BI; 7), subarachnoid hemorrhage (SAH; 6), and brainstem hemorrhage (BH; 13). The localization in 32 cases, the exceptions being those of SAH was in the thalamus (6.2%), midbrain (31.2%), pons (37.5%) and midbrain-pons (2.5%). PH was not necessarily confined to elderly patients. The sex ratio (man/woman) was 20/18. The most common time for PH seems to be the evening. The cause of PH does not necessarily have a close relationship with the timing of withdrawal of the hemorrhage and edema. In 10 cases of tumor in which PH appeared preoperatively, the hallucination disappeared after removal of the tumor in all. For SAH, the duration of PH was from 3 to 12 days, which is interestingly consistent with that of symptomatic vasospasms. For BI and BH, although the hallucination usually disappeared in parallel with withdrawal of the causal pathology, PH continued even at the chronic stage in some cases. There was no particular difference in hallucination contents with the causal pathology of PH. The most frequent hallucinations involved people or figures, i.e., approximately 80%. Then, animals (dogs, cats, snakes, etc.), insects, and fishes were also frequently involved. Sleep abnormality was observed in 27 cases (71%). Agitation was observed in 18 cases (47.3%), in all of which it was accompanied by sleep abnormality. Increased intracranial pressure was observed in 8 (21%). Hydrocephalus was observed in 4 (10.5%). Prior visual impairment was recorded in 7 (18.4%). ?Conclusioins] On the analysis of 38 cases with PH, it became clear that PH occurs not only in focal brainstem intrinsic stroke lesions, but also in extrinsic lesions like subarachnoid hemorrhage and brain tumor compression. Reciprocal connections between the serotonergic and cholinergic systems, especially between the raphe and the pedunculopontine tegmental nucleus, may be impaired in the reticular formation. Surprisingly, these lesions do not directly involve the retino-geniculocortical system, which is generally considered to be required for the appreciation of complex forms and color. The association between sleep-awake disruption and PH may occur because lesions affecting the raphe nucleus cause a transient increase in ponto-geniculate-occipital spikes, which may be related to reorganization and plasticity. Although increased intracranial pressure and hydrocephalus were considered as insults to the "hallucination-suppression mechanism?, they do not seem to be significant as a cause of PH. The clinical manifestations of PH are often mistaken for those of postoperative "altered sensorium? or "psychosis?. Medical doctors who manage organic brain lesions should take PH into consideration.