[Depressive pseudodementia in early Parkinson's disease: lessons from a case with long-term follow-up]

A common observation in neurological practice is parkinsonism with concomitant cognitive decline, an association that usually arises from various underlying degenerative or vascular conditions, most of which are untreatable. An elderly woman with no history of psychiatric disease presented complaining of memory and cognitive impairment serious enough to interfere with daily life activities over the preceding year. She soon developed a predominantly left-sided tremor, rigidity and bradykinesia. She had had only 2 years of formal education. Neuropsychological assessment showed poor performance on Wechsler memory scale sub-items, as well as constructional apraxia, dyscalculia, reasoning difficulties and gross information deficits. A 3-month trial course of levodopa was followed by dramatic improvement in both parkinsonian symptoms and cognitive performance, including a 7-point gain in the Mini-Mental Status Examination score. At the same time, the Beck Depression Inventory score fell from 27 (baseline) to 18. Over the 10-year follow-up period the patient developed late levodopa syndrome and a persistent but mild dysthymic disorder, but never manifested dementia as defined by DSM-III-R criteria. This patient's case illustrates three important principles. First, although parkinsonism is known to be preceded by depressive episodes, particularly in a subgroup of younger patients, the symptoms of the elderly patient whose Parkinson's disease is foreshadowed by depression can mimic depressive pseudodementia, potentially leading to diagnostic confusion. Second, impaired motivation and disturbances in cognitive function are different from mood disorders, as the former involve the mesolimbic/mesocortical dopamine system, explaining the beneficial effect of levodopa on motivation and cognition in this patient even as mood was unaffected. Finally, depressive pseudodementia in Parkinson's disease does not necessarily herald the development of organic dementia in the long term.