Head of the geriatric department in a Parisian hospital, Prof. A. is used to producing a common reference object to describe Alzheimer’s disease to his patients by resorting to a description of a house with a damaged staircase which does not allow access to the rooms of the upper floor, symbolizations of their preserved intellectual faculties. For this purpose, the doctor convokes semio-discursive resources to accomplish the descriptive activity and organize his verbal turn, mainly combined with iconic gestures with metaphorical value. This metaphorical meaning lies in the partial semantic incongruity observable during the multimodal performance between the conventional schematization of gestures and the schematization of affiliated verbal expression. By this verbal and gestural scene, the geriatrician tries to relay and share medical knowledge in a didactical way while leaving the patient free to acknowledge the metaphor as an explanation of the disease.