Decision-Making Impairment May Precede Limb Apraxia in Corticobasal Degeneration

To the Editor: Corticobasal degeneration (CBD) is characterized by asymmetric akinesis and rigidity, dystonia of the upper limb, apraxia, myoclonus, and dementia.¹ Even if cognitive deficits, in particular of executive functions, are associated with CBD,² no findings are available about orbitofrontal executive functions,² usually assessed by decision-making tasks, such as the Iowa Gambling Task (IGT).³ In our movement-disorder tertiary clinic, we consecutively assessed patients who present signs compatible with a diagnosis of Parkinson's disease⁴ or parkinsonism with this task. Two of these patients, initially diagnosed with parkinsonism, subsequently developed a manifest upper-limb apraxia and were clinically diagnosed with CBD.

One patient, Ms. DB, 60 years old, came to our attention in April 2008 for symptoms of bradykinesia and left upper-limb rigidity. She underwent a DaT-SCAN SPECT (bilateral hypocaptation in both putamen nuclei, more marked on the right), an RMI (showing diffuse cortical atrophy, more marked in the right parietal-prefrontal-insular cortex), and an 18-FDG-PET (mild hypometabolism in the right temporo-prefrontal cortex, the right ventral temporal cortex, and the right thalamus). Cognitively, she presented mild executive dysfunction. In March 2009 she developed a left upper-limb apraxia (Movement Imitation Test⁵: normal score >62; right upper limb: 67; left upper limb: 26). In November 2009 apraxia also affected the right upper limb (Movement Imitation Test: right upper limb: 47; left upper limb not assessable).

Another patient, Mr. EH, a 66-year-old, right-handed man, came to our attention in September 2007 for symptoms of bradykinesia and right upper-limb rigidity. He underwent a DaT-SCAN SPECT (bilateral hypocaptation in both putamen nuclei, more marked on the left, and in the left caudate nucleus) and an 18-FDG-PET (marked bilateral hypometabolism in the parieto-prefrontal cortex, more marked on the left). He presented mild impairment of memory and executive functions. In January 2009 he developed a marked right-limb apraxia (Movement ImitationTest⁵: left upper limb: 63; right upper limb: 20).

During their baseline assessments, at the onset of parkinsonism and before the appearance of upper-limb apraxia, both CBD patients performed the IGT, and were unable to develop a strategy of choice from more advantageous decks along the task. Mr. EH received a final score of 0, choosing equally from advantageous and disadvantageous decks in the latter two blocks of choices. Ms. DB received a positive final score (+18), selecting almost all advantageous decks in Blocks 2 and 5 and selecting almost all disadvantageous decks in Block 4. This pattern reflected more impulsive, perseverative behavior than a progressive development of an explicit strategy of choice. Instead, patients with de novo Parkinson's disease were able to develop a strategy of choice from more advantageous decks along the IGT.⁴ These neuropsychological findings suggest that, in CBD patients, decision-making may be impaired early in the course of the disease and may sometimes precede the appearance of upper-limb apraxia. These findings also suggest that the IGT is a useful task to detect early cognitive impairments in patients with parkinsonism whose clinical symptoms are suggestive of CBD.