Hallucinations are common in elderly. Understanding the diverse aetiologies and behavioural reactions to hallucinations is vital to provide the best level of care.

An 85-year-old man, with several cerebrovascular risk factors (dyslipidaemia, atrial fibrillation, previous ischemic-stroke), developed cognitive impairment after an acute confusional state (two years before), characterized mainly by short-term memory deficit and executive dysfunction. In the meantime, he started recurrent periods of multimodal hallucinations, with predominant sundowning pattern, along several months, comprising complex visual hallucinations, with which he interacted, sometimes combined with haptic hallucinations, describing a plastic sensation in his hands, and manifesting carphologia and psychomotor agitation. Insight into the hallucinatory nature of the phenomenon recovered after a few hours. The neurologic examination revealed partial left oculomotor nerve palsy (left exotropia and diplopia on the right conjugate eye movement), postural instability, slight truncal bradykinesia, and symmetrical rigidity. The neuroimaging studies confirmed small vessel disease with leukoaraiosis and lacunar infarcts in the lentiform nuclei. No lesions were observed within the visual pathway nor the midbrain.

This case leads to an interesting discussion regarding the differential diagnosis of combined hallucinations in elderly.

The presence of the oculomotor nerve palsy selectively affecting somatic fibers, raised the suspicious of peduncular hallucinosis, in the framework of vascular disorder. Combination of visual and tactile may occur in peduncular hallucinosis. However, the neuroimaging studies did not reveal ischemic lesions in the midbrain. Therefore, the most plausible aetiology for hallucinations is a demential syndrome, namely a vascular dementia, considering the findings on neuroimaging. Additionally, a Lewy-body disease (LBD) cannot be ruled out by virtue of the clinical picture of recurrent well-formed visual hallucinations, symptom fluctuation and slight parkinsonism, or even a Lewy-body variant of Alzheimer disease, considering the presence of amnestic symptoms. Tactile hallucinations have been described in alfa-synucleinopathies. Contrarily to Parkinson disease, when the LBD patients touch their visual hallucinations, the perceived objects often do not disappear and may experience specific texture and thermic sensations.

Future research would benefit from a more detailed investigation of the profile of similarities and differences in hallucinations across clinical disorders to facilitate differential diagnosis.