Suspecting Dementia: Canaries, Chameleons and Zebras
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How to do it Suspecting dementia: canaries, Pract Neurol: first published as 10.1136/practneurol-2021-003019 on 2 July 2021. Downloaded from chameleons and zebras Jeremy C S Johnson ,1 Laura McWhirter,2 Chris J D Hardy,1 Sebastian J Crutch,1 Charles R Marshall,3,4 Catherine J Mummery,1 Jonathan D Rohrer,1 Martin N Rossor,1 Jonathan M Schott,1 Rimona S Weil ,1 Nick C Fox,1 Jason D Warren1 1Dementia Research Centre, ABSTRACT dementia in the first place and deciding why UCL, London, UK The early and accurate diagnosis of dementia this is not ‘just’ Alzheimer’s disease. 2Centre for Clinical Brain Sciences, University of is more important than ever before but Dementia is a syndrome that can be defined Edinburgh, Edinburgh, UK remains challenging. Dementia is increasingly very generally as a progressive decline in 3 Preventive Neurology Unit, the business of neurologists and, with ageing cognitive function and/or behaviour that Wolfson Institute of Preventive populations worldwide, will become even Medicine, London, UK impacts daily life functioning. As such, it 4Department of Neurology, more so in future. Here we outline a practical, has a multiplicity of causes. Most of these Royal London Hospital, London, symptom- led, bedside approach to suspecting are neurodegenerative pathologies that are UK dementia and its likely diagnosis, inspired by not presently reversible; however, the rare Correspondence to clinical experience and based on recognition of exceptions are not to be missed. A key theme Prof Jason D Warren, Dementia characteristic syndromic patterns. We show how in dementia (especially in neurodegenerative Research Centre, University clinical intuition reflects underlying signature disease) is that the causative pathologies College London, London WC1N profiles of brain involvement by the diseases 3BG, UK; jason. warren@ ucl. initially target certain brain functions rela- ac. uk that cause dementia and suggest next steps tively selectively, due to a predilection of that can be taken to define the diagnosis. We pathogenic proteins to involve particular Accepted 20 April 2021 propose ‘canaries’ that provide an early warning 3 Published Online First brain networks. Over time, these signature 1 July 2021 signal of emerging dementia and highlight the patterns become obscured as the spread of ‘chameleons’ that disguise or mimic this, as well pathological change leads to convergent, as the ‘zebras’ that herald a rare (and sometimes widespread damage and impairment. The curable) diagnostic opportunity. window of greatest opportunity for accurate diagnosis (and anticipated interventions) http://pn.bmj.com/ pn. bmj. com is therefore early- stage disease. Appreci- ating how profiles of brain damage relate to INTRODUCTION cognitive deficits is key to deciding which As the number of people worldwide with diseases are likely in patients presenting with dementia approaches 50 million, the need suspected dementia. for early and accurate diagnosis is more Here we outline a symptom- led, bedside on September 29, 2021 by guest. Protected copyright. urgent than ever.1 Timely diagnosis avoids approach to suspecting dementia that we the limbo of diagnostic uncertainty and futile have found useful in busy neurological clinics. cycles of investigation, equips patients and First, we consider clues that help one decide families to engage appropriate support and whether or not cognitive decline is present to plan for the future, and directs rational and, if so, the likely cause. We show how and appropriate management.2 It will also these clues predictably reflect underlying be essential for the effective deployment of signature patterns of brain involvement by disease- modifying therapies that are on the causative pathologies and suggest next steps horizon. However, the early diagnosis of that can be taken to define the diagnosis. As dementia is challenging and remains pecu- with many other disorders, the neurologist’s © Author(s) (or their liarly reliant on clinical judgement (box 1); essential task is to identify ‘canaries’ that employer(s)) 2021. No the target diseases are complex and affect provide an early warning signal of emerging commercial re- use. See rights aspects of higher brain function that are disease, avoid being misled by ‘chameleons’ and permissions. Published by BMJ. generally not assessed in routine neurolog- that disguise or mimic this and remain alert ical practice. Treatises on dementia conven- to the occasional ‘zebra’ that heralds a rare To cite: Johnson JCS, McWhirter L, Hardy CJD, et al. tionally list the clinical features of particular (and sometimes curable) diagnosis. Pract Neurol 2021;21:300– diseases—in the trenches, however, the We suggest some general principles and 312. biggest challenge is often suspecting tools for cognitive assessment in box 1 and Johnson JCS, et al. Pract Neurol 2021;21:300–312. doi:10.1136/practneurol-2021-003019 1 of 14 How to do it figure 1 and outline a bedside framework for cognitive Pract Neurol: first published as 10.1136/practneurol-2021-003019 on 2 July 2021. Downloaded from Box 1 Some principles of bedside cognitive history taking and examination in table 1. Diagnostic assessment canaries based on characteristic patterns of cerebral History taking involvement are listed in table 1; potential pitfalls are listed in table 2, chameleons in table 3 and zebras in table 4. ► History is the most important aspect of successful dementia diagnosis. DOES THIS PATIENT HAVE DEMENTIA? ► Obtaining a history from reliable informants who know the patient well is integral and interviewing Distinguishing early dementia from the ‘worried well’ or a them separately may encourage sharing of sensitive or ‘functional’ cognitive disorder is an increasingly frequent embarrassing clues to the diagnosis. challenge faced by neurologists as public awareness and anxiety about dementia continue to increase.4 A func- ► A minute or two spent putting the patient and family at ease is well invested. tional cognitive disorder should be considered if there are positive features of internal inconsistency, that is, ability ► How organised and detailed patients seem when describing their symptoms is informative, particularly if to perform a task well at certain times, but with signif- at odds with performance on formal cognitive tests. icant difficulty when it becomes the focus of attention. The person who gives a detailed (or even overinclusive) ► Interpretation of cognitive or behavioural changes depends on an appreciation of the patient’s account of their memory lapses, attributes their difficul- sociocultural background, education, occupation, ties eloquently to specific past events and who is substan- premorbid language skills, any pre- existing specific tially more concerned about their cognitive function than developmental or other deficits, and medical and their partner, children or colleagues—often attending psychiatric history (including medications). clinic unaccompanied—is more likely to be anxious or to have a functional cognitive disorder than dementia. ► Cognitive concerns will most frequently be framed as a non- specific‘memory’ problem: this is the most People with obsessional personalities are more prone ubiquitous of several potential ‘pitfall’ symptoms that to overinterpret the imperfections of normal memory. must be deconstructed (see table 2). There is often a flavour of wavering concentration, such as being unable to remember why one has entered ► Domains of cognitive function and behaviour that may not be volunteered should also be explored (as these a room, misplacing household items in odd locations help define the cognitive profile), framing these as (eg, keys in the fridge) or ‘going blank’ during a conver- questions about functioning in daily life. sation only to have the required information re- emerge soon afterward. Cognitive testing frequently generates ► Particularly in younger people, a detailed family history is essential (including parents’ diagnoses and age at considerable anxiety, inducing ‘thought-blocking’ and death if relevant, and the ages of any siblings). performance may vary widely between assessments, often Examination leading to marked inconsistencies (disastrous test scores despite evident competence in daily life). This contrasts http://pn.bmj.com/ ► It is first essential to establish that the patient is alert and cooperative and that their peripheral vision and with the ‘face-saving’, humour and minimisation often hearing are adequate (or corrected as appropriate). seen in Alzheimer’s disease, or indifference in diseases where insight is impaired. However, particularly in older ► Observing the patient’s conduct and interaction with the examiner and others is often telling (it may point patients, functional cognitive impairment may signal an to frontal lobe dysfunction more clearly than any test; emerging neurodegenerative process which declares itself see table 2). subsequently. on September 29, 2021 by guest. Protected copyright. Depression or other primary psychiatric diagnoses must ► To corroborate the history and to build a diagnostic profile of cognitive deficits, it is helpful to have a not be overlooked—these are potentially treatable and scheme for testing cognition (a ‘walk around the undetected carry significant risk of harm. There is often a brain’, table 1), armed with some tools to elicit history of previous psychiatric episodes, though this may cognitive deficits (figure 1): the cognitive profile not be volunteered. Core depressive symptoms are low in