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Corticobasal ganglionic degeneration and/or frontotemporal dementia?
  1. Toronto Western Hospital, Toronto, Canada

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    I read with interest the recent paper by Mathuranathet al 1describing two patients with the pathology of corticobasal ganglionic degeneration (CBD), the first presenting with the syndrome of frontotemporal dementia and the second with a mixed picture dominated by progressive aphasia. The concept that CBD may present with clinical features distinct from the “perceptuomotor” syndrome widely recognised as “classic” of the disorder is not new. However, until recently it had generally been thought that these cases represented the minority and thus could be considered “atypical”. However, knowledge about this disorder has evolved since our group and others reported the first large series. I think that in 2000 it is not appropriate to quote our 1994 book chapter2 stating that “Frank dementia or language dysfunctions are said to be rare and, if present, are mild, and typically occur late in the course of the disease,”1 as current wisdom. Within 2 years of that book chapter ourselves and others were reporting alternative presentations for this pathology and most recently we have published the clinical-pathological experience of the Canadian Brain Tissue Bank in a paper that was presumably in press at the time that the paper of Mathuranath et al was being reviewed.3 In this study we found that of 13 patients proved pathologically to have CBD, nine presented with cognitive or language disturbances, only one failed to show dementia during the course of the illness and only four were diagnosed as having CBD in life. Since that time, a 14th patient has come to necropsy whose presentation was that of primary progressive aphasia.

    There have also been patients reported in the literature by ourselves and others with alternative neuropathological disorders presenting with clinical features that were mistaken for the “classic” (but now it seems not the commonest) phenotype of CBD including progressive supranuclear palsy, Pick's disease, motor neuron inclusion body dementia, Alzheimer's disease, and familial frontotemporal dementia due to chromosome 17 mutations.

    In summary, clinical and pathological experience at the turn of the century strongly supports the conclusions of Mathuranathet al. Clinical phenotypes have not proved to be restricted to specific pathological substraits and several different clinical phenotypes may be caused by the same underlying pathology, probably largely dependent on the anatomical distribution of greatest involvement. Where I mainly take issue with the authors is in their belief, which largely justifies their report, that a clear distinction between CBD and FTD is “currently accepted”. The cumulative literature since our 1994 review, most recently culminating in a monograph on a topic,4 indicates that CBD is no longer thought of as a predominately extrapyramidal disorder that is distinct and unrelated to frontotemporal dementia.