Impairment of Affective Theory of Mind in Corticobasal Degeneration

To the Editor: The term Theory of Mind (ToM) refers to the ability to attribute mental states to others and to predict, describe, and explain behavior on the basis of such mental states.¹ Usually assessed in subjects with various psychiatric disorders such as schizophrenia, autism, depression, and personality disorders, in recent years researchers have also started to assess ToM ability in patients with neurodegenerative diseases.^2,3 These studies showed that ToM processes may be differently affected by neurodegenerative processes: for example, patients with Alzheimer's disease and patients with Parkinson's disease may present difficulties related to the cognitive ToM component Inference About Others' Beliefs more than to the affective ToM component Inference About Others' Feelings, whereas patients with frontotemporal dementia may present impairments of both ToM components. To our knowledge, ToM has never been investigated in patients with corticobasal degeneration (CBD), a progressive neurodegenerative disease that typically presents with asymmetrical parkinsonism and cognitive dysfunction.⁴ We report on the case of an affective ToM impairment in a case of clinically diagnosed CBD. “Ms. TD,” a 62-year-old, right-handed, married, retired woman, came to our attention in September 2010 because of the appearance of difficulties of memory, mental calculation, and praxis in everyday life, associated with mild depression. Ms. TD underwent a neurological examination, showing a clinical picture of upper-limb tremor, more marked on the left side, and limb apraxia. She also underwent electroencephalography, which showed bilateral temporo-parietal alterations; a computed tomography, showing cortical atrophy; and an 18-FDG positron emission tomography, showing a bilateral hypometabolism in the frontal-temporal-parietal cortices, more marked in the right hemisphere. The patient did not undergo a magnetic resonance imaging scan because of the presence of a metallic implant. The global cognitive status evaluation showed mild impairment (Mini-Mental State Exam raw score: 23/30). Her Movement Imitation Test yielded scores suggestive of a bilateral limb ideomotor apraxia, mildly left-lateralized. At the neuropsychological evaluation, she also presented preserved memory functioning and a mild impairment of executive and visuospatial functions. This clinical picture was suggestive of a clinically diagnosed corticobasal degeneration.⁴ In this patient, we assessed affective ToM with the Reading the Mind in the Eyes (RME) test,⁵ consisting of the presentation of photographs of the eye region of human faces; participants are required to choose which word best describes what the individual in the photograph is thinking or feeling. For the control of possible visual difficulties interfering with the task, participants are also asked to decide the gender of each individual represented only by the eye region. TD had a score of 17/36 in the RME task and a score of 30/36 in the gender control task. We deemed that the presence of mild visuospatial difficulties could not totally explain impaired performance in the RME, considering the better performance in the gender control task. This finding suggests, as previously reported for behavioral-variant frontotemporal dementia,² that when the neuropathology affects orbital and ventromedial portions of the prefrontal cortex (as shown by the 18-FDG PET), performances in tasks of affective ToM may be impaired.