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The concepts of potentially reversible cognitive impairment in general, and the reversible dementias in particular, remain controversial. The prevalence of these conditions depends to a great extent on the definitions used and on the population studied. Also, the definition of those cases with potentially reversible conditions that actually do reverse remains a critical aspect in assessing these conditions.
In their article, Hejl et al1 present the results of a prospective study to investigate the prevalence of potentially reversible causes of cognitive decline in consecutive patients presenting to a tertiary medical centre memory clinic. The description that they provide of a large cohort provides an important contribution to our understanding of this condition. However, as was mentioned by the authors in the discussion, the rather high prevalence (19%) of potentially reversible causes detected must be regarded with some caution. Also, while no data are presented regarding the follow up of those patients where a potentially reversible cause was identified, the authors nevertheless conclude “that treatment may improve or restore intellectual functions.”
As was mentioned by the authors, one of us (AMC) has previously described the prevalence of reversible dementias, with 13.2% of cases having a potentially reversible cause, while only 3% fully resolved on treatment.2 In that review of the literature, as in the study by Hejl et al, most of the studies originated from secondary or tertiary centres. In a recent meta-analysis by AMC,3 where a much higher proportion of studies than previously emanated from either outpatient departments or were community based, it was shown that regardless of potential reversibility, the true prevalence of reversed dementias is actually less than 1%.
We thus feel that although it is important to diagnose and treat concomitant conditions in patients suffering from cognitive decline, one should exercise great caution in describing possible causes of cognitive decline and dementia as either potentially or fully reversible.
We are grateful for the opportunity to comment on the important issue raised by Dr Dwolatzky and Dr Clarfield regarding the true prevalence of reversible dementias. In our paper we investigated the prevalence of potentially reversible aetiology and comorbidity in 1000 consecutive patients referred to an outpatient memory clinic based in neurology. In the whole group of patients 19% presented with a potentially reversible condition, which was evaluated as the primary cause of the symptoms leading to referral. However, in patients meeting the clinical criteria for dementia the prevalence was only 4%. For potentially reversible concomitant conditions the prevalence was 23%. Thus, potentially reversible conditions are most common in patients with cognitive symptoms, less common in patients meeting the criteria for dementia, and comparatively common as comorbidity in both groups.
Dr Dwolatzky and Dr Clarfield report that in their future meta-analysis for publication in 2003 the “true” prevalence of reversed dementias is less then 1%. With reference to our results in patients with dementia we are not surprised about the very small prevalence of truly reversed dementias.
As we have already discussed in our report, both the setting of the study and the definition of potentially reversible conditions may influence the prevalence found. Also a systematic prospective design, as in our study, may reveal a higher prevalence than retrospective studies. Thus, even though one cannot apply our findings directly to the conditions in other settings, the study provides evidence that potentially reversible conditions are not rare. They were most common in younger patients and in patients with mild cognitive symptoms not sufficiently severe to meet international criteria for dementia.
The most frequent potentially reversible conditions were depression, hydrocephalus, alcohol dependence syndrome, metabolic disorders, and space occupying lesions. Even if treatment of these conditions may not always lead to full reversal of cognitive symptoms or dementia, the identification of the disorders is crucial to the management of the patient and important to prevent a misdiagnosis of Alzheimer’s disease. In conclusion, a systematic search for potentially reversible conditions is relevant and important, even when full reversal of the cognitive symptoms may be unlikely.