Proactive interference apraxic agraphia: a writing and drawing disorder associated with corticobasal syndrome.

Proactive interference is when a previously performed task impairs performance on a current task. It is often associated with memory tasks and has not been reported to interfere with writing or drawing. We evaluated a left-handed man diagnosed with corticobasal syndrome who had a two-year history of progressive agraphia. On the sentence writing and clock drawing tasks, he initially wrote letters and numbers correctly but revealed an increase of movement errors as the tasks progressed. We propose the term "proactive interference apraxic agraphia" for this novel disorder. Prefrontal dysfunction may cause an impairment in disengaging from previously activated motor programs.